Dean PJA, Seiss E, Sterr A (2009) Advance movement preparation in hemiparetic patients: Electrophysiological indices.,
Hope C, Seiss E, Dean PJA, Williams K, Guinn A, Sterr A (2011) Response time slowing by glucose dependent on strength of stimulus response association: investigations with the flanker task, Frontiers in Human Neuroscience: ICON XI, Conference Abstracts Frontiers
Previous studies showed that performance in difficult tasks, such as memory tasks, can be improved by glucose administration (Riby, 2004). Whether glucose has similar effects on sensorimotor conflicts is unclear. Here we present 2 behavioural experiments with a double-blind placebo-controlled design to investigate glucose effects on response conflicts in a flanker task. In both experiments, blood glucose levels (BCG) levels were kept around 6.5 Mmol/litre in the glucose and 5 Mmol/l in the placebo condition. In experiment 1, 12 participants (age: 25.1 years) performed an arrow version of the flanker task. Results showed that reaction times (RTs) of block 1 were 24 ms slower in the glucose (436 ms) than the placebo condition (412 ms) but not for subsequent blocks. The absence of the glucose effect in blocks 2-8 can be explained by the strong stimulus-response association (SRA) in the arrow-version of the flanker task. Experiment 2 tested this explanation by using a flanker-task version with weaker letter-key associations whereby new SRAs had to be learned after every block. Data from 12 participants (age: 20.1 years) confirmed the previous finding of slower reaction times in the glucose condition (437 ms) with an increase of 40 ms compared to the placebo condition (397 ms). Critically this effect was maintained throughout the experiment. However, the response conflict, indexed by the difference between congruent and incongruent trials, was not affected by glucose. Our data suggest that sensorimotor processes can be slowed by glucose, a finding which contrasts reports of facilitatory effects of glucose on cognition (Riby, 2004). In addition the critical variable for glucose-induced RT effects appears to be the strength of SRA rather than the actual response conflict.
Kranczioch C, Mathews S, Dean PJA, Sterr A (2009) On the equivalence of executed and imagined movements: Evidence from lateralized motor and nonmotor potentials, Human Brain Mapping 30 (10) pp. 3275-3286
The neural simulation theory assumes that motor imagery and motor execution draw on a shared set of mechanisms underlying motor cognition. Evidence is accumulating that motor imagery and motor execution have many common features. The extent of the similarity and whether it spreads into the preparation phase is however unclear. This study used electroencephalographic recordings to compare the effects of providing advance information about upcoming movements on preparatory processing in a motor imagery and execution paradigm. Event-related potential data were recorded in a priming task where participants were cued to perform simple or complex finger movements. We hypothesized that a high degree of functional similarity of motor imagery and motor execution should be reflected in similar alterations of lateralized preparatory activity. Lateralized preparatory activity was indeed very similar, showing both motor-related (lateralized readiness potential, LRP) and cognitive components (anterior directing-attention negativity or ADAN, late directing-attention positivity or LDAP). Dipole analysis revealed that LRP, ADAN, and LDAP sources were very comparable for motor imagination and execution. Results generally support the idea of common underlying functional networks subserving both the preparation for execution and imagery of movements. They also provide a broader context for this notion by revealing similarities in cognitive components associated with the movement tasks. © 2009 Wiley-Liss, Inc.
Seiss E, Hope C, Guinn A, Dean PJA, Sterr A (2013) The effect of elevated blood sugar levels on encoding and retrieval in averbal memory task, Psychophysiology 50 (S1) pp. S92-S93 Wiley-Blackwell
Previous studies suggest that oral glucose administration directly facilitates declarative memory encoding and retrieval (Sünram-Lea et al., 2002; Manning et al., 1992). However, glucose could indirectly facilitate memory encoding by already enhancing pre-mnemonic sensory or lexical/semantic processes, which produce important substrates for memory encoding. In the present study we used ERP measures combined with a robust placebo-controlled double-blind glucose elevation protocol to (1) replicate the glucose facilitation effect on declarative memory performance, and (2) determine whether glucose modulates pre-mnemonic or mnemonic processes at the encoding and retrieval stage. EEG was collected from 32 electrodes while participants performed a word recognition task under conditions of elevated (6.5 ± 0.12 mmol) and normal (4.57 ± 0.12 mmol) blood glucose levels. In line with the literature, recall rates were better in the glucose condition. Glucose also enlarged the LPC component, which is functionally linked to memory encoding and consolidation processes. Glucose also modulated VEPs (P1, N1), the P300, and the N400, a marker of pre-mnemonic lexical/semantic processing. The N400 amplitude positively correlated with memory performance. At the recognition stage similar effects on VEPs and the P300 were observed, and glucose numerically enhanced the FN400, while reducing the LP. In summary the glucose facilitation of declarative memory may be enacted through effects on earlier information processing stages as well as later memory-specific processes.
Sterr A, Dean P (2008) Neural correlates of movement preparation in healthy ageing, European Journal of Neuroscience 27 (1) pp. 254-260
Motor disorders increase dramatically with age; however, little is known about non-clinical ageing of motor control mechanisms and their respective neural correlates. With the present experiment we aimed to study age effects on advance movement preparation, a key characteristic of motor behaviour that is known to involve premotor and primary motor circuits. The respective brain regions are subject to age-related brain atrophy of grey and white matter, and we therefore hypothesized that motor preparation mechanisms may be altered in older persons. Using a motor priming paradigm, performance data and event-related potentials were recorded in older (68-83 years) and younger (21-25 years) participants. The effect pattern observed for the younger group fully replicated previous findings, showing significant reaction time benefits and greater foreperiod activity for valid trials, as well as lateralized activation over motor regions. In older participants, the validity effect was insignificant, which corresponded to markedly reduced foreperiod amplitudes and the absence of lateralized activity. At the same time, the event-related potential showed a frontocentrally distributed positive component peaking in the P300 latency range after presentation of the prime. The amplitude of this potential was enhanced in elderly compared with young participants. The data suggest that the information processing related to the anticipation and preparation of an upcoming response changes substantially with age. In contrast to younger participants, older participants show no indication of effector-specific activation and recruit frontal areas in anticipation of a response signal. It is therefore not only movement execution that changes with age but also motor cognition.
Dean P, Minarik T, Opitz B, Sterr A (2016) Creatine supplementation for symptom alleviation after mild traumatic brain injury, BRAIN INJURY 30 (5-6) pp. 662-662 TAYLOR & FRANCIS INC
Sterr A, Dean PJA, Sato JR, Vieira G, Conforto AB, Shen S (2013) Cortical thickness changes in the non-lesioned hemisphere associated with non-paretic arm immobilization in modified CI therapy, NeuroImage: Clinical 2 (1) pp. 797-803
Recent evidence suggests that immobilization of the upper limb for 2-3 weeks induces changes in cortical thickness as well as motor performance. In constraint induced (CI) therapy, one of the most effective interventions for hemiplegia, the non-paretic arm is constrained to enforce the use of the paretic arm in the home setting. With the present study we aimed to explore whether non-paretic arm immobilization in CI therapy induces structural changes in the non-lesioned hemisphere, and how these changes are related to treatment benefit. 31 patients with chronic hemiparesis participated in CI therapy with (N = 14) and without (N = 17) constraint. Motor ability scores were acquired before and after treatment. Diffusion tensor imaging (DTI) data was obtained prior to treatment. Cortical thickness was measured with the Freesurfer software. In both groups cortical thickness in the contralesional primary somatosensory cortex increased and motor function improved with the intervention. However the cortical thickness change was not associated with the magnitude of motor function improvement. Moreover, the treatment effect and the cortical thickness change were not significantly different between the constraint and the non-constraint groups. There was no correlation between fractional anisotropy changes in the non-lesioned hemisphere and treatment outcome. CI therapy induced cortical thickness changes in contralesional sensorimotor regions, but this effect does not appear to be driven by the immobilization of the non-paretic arm, as indicated by the absence of differences between the constraint and the non-constraint groups. Our data does not suggest that the arm immobilization used in CI therapy is associated with noticeable cortical thinning. © 2013 The Authors. Published by Elsevier Inc. All rights reserved.
Dean PJA, Sterr A (2008) Advance movement preparation is intact in
hemiparetic patients: Validity effects seen in a
response priming task with the affected arm, Brain Injury Supplement 1 (22) pp. 168-169
Objectives: Brain injury, including stroke, can cause
a partial or total loss of movement of the body
contralateral to the affected area. Movementexecution is dependent on movement preparation
for optimal motor performance and studying
advance movement preparation in those with
hemiparesis will help elucidate whether this process
is involved in the observed motor impairment.
Motor control can be studied using response
priming paradigms, in which prime stimuli give
some degree of prior information that allows
preparation of the forthcoming response.
Dependent on the level of advance information,
participant?s reaction times are modulated, with
reaction time costs for incorrect prime information
and reaction time benefits for correct information
when compared with an uninformative prime. This
reaction time pattern is termed the validity effect
and is indicative of cognitive processing of the
prime and subsequent movement preparation. The
presence of such an effect in hemiparetic patients
would reveal this ability to be intact, which would
aid in the construction of therapeutic interventions.
Method: Twenty-nine participants with hemiparesis
(at least 1 year post-injury) and 16 age matched
control (non-brain injured, non-hemiparetic) subjects
were recruited. They performed a response
priming task whereby they were expected to press
buttons with their hands dependent on a left or right
button cue. Priming stimuli presented before that
were either informative (Valid) or uninformative
(Neutral). Reaction times were recorded for the
affected and unaffected arms.
Results: Within-group means comparison revealed a
significant validity effect in control and hemiparetic
participants, with both groups taking longer to
respond to the neutral prime trial than to the valid
prime trial. For the affected arm this difference was
210 ms, for the unaffected arm this was 125 ms and
for controls this was 58 ms. In addition, hemiparetic
participants were significantly slower than control
participants in both affected and unaffected arms.
However, the affected arm reaction time differed
from the controls to a greater extent (325 ms for
valid prime) than the unaffected arm (179 ms for
Conclusions: Our study shows that hemiparetic
participants are generally slower to respond to
visual stimuli than a control group, as would be
expected in a group with motor impairment.
However, despite the deficit the validity effect is
preserved for both their affected and unaffected
Dean PJA, Perkins L, McNamara A, Sauseng P, Sterr A (2014) A novel method for acquiring cognitive data after brain injury and during follow-up: The use of mobile technology in a Visuo-Spatial Working Memory Task, Brain Injury 28 (5-6)
Objectives: To investigate the utility of mobile touch-screen technology in the assessment of cognitive function in everyday contexts. A novel visuo-spatial working memory (VSWM) task was chosen here to (a) test the technology in the field and (b) examine VSWM performance of participants with mTBI under everyday conditions. Methods: A VSWM task was administered using PsyApp software (www.psyapp.co.uk
) on a 10" tablet computer to participants with a previous mTBI (n=15) and those without (n=15). mTBI was diagnosed using ICD-10 criteria and post-concussion symptoms were recorded using the Rivermead Post-Concussion Questionnaire (RPQ). Participants were tested in a busy cafe and were shown an arrangement of 3, 4, 5, 6, 7 or 8 dots for 500 milliseconds (encoding), followed by a blank screen for 2 seconds (retention), then asked to press the touch-screen in the spatial positions occupied by the dots in the encoding phase. The distance between the actual and recalled dot locations was calculated as a measure of precision. The task was presented in two sessions of six blocks (one of each condition, lasting
30 minutes) with a 30-minute rest between sessions. Fatigue measures were calculated using the Piper Fatigue Scale at the start of each session and at the end of the experiment. Results: As expected, precision was lower in the harder tasks (p<.001 dot:="" to="" mm="" and="" participants="" were="" more="" accurate="" in="" the="" second="" session="" compared="" first="" e.g.="" however="" there="" was="" no="" difference="" performance="" between="" groups="" control:="" a="" correlation="" seen="" higher="" rpq="" score="" lower="" precision="" dot="" condition="" with="" mtbi="" for="" both="" sessions="" p="" r="">-ý0.6). There was also a correlation between higher overall fatigue (Total PFS score, p<.05 r="ý=0.4)" and="" lower="" precision="" in="" the="" second="" session="" of="" dot="" condition="" across="" participants.="">Conclusions: Touch-screen technology enabled the acquisition of a novel measure of precision in a VSWM task in an everyday context. Precision decreased with difficulty level, suggesting that the protocol and measure are valid. This technology can be further adapted to gain more in-depth and regular data acquisition in a variety of realworld situations. However, there was no significant difference in performance between groups, despite interesting correlations with post-concussion symptoms, fatigue. Previous VSWM studies report difference
Sterr A, Dean PJ, Szameitat AJ, Conforto AB, Shen S (2013) Corticospinal tract integrity and lesion volume play different roles in chronic hemiparesis and its improvement through motor practice., Neurorehabil Neural Repair 28 (4) pp. 335-343
BACKGROUND: Initial evidence suggests that the integrity of the ipsilesional corticospinal tract (CST) after stroke is strongly related to motor function in the chronic state but not the treatment gain induced by motor rehabilitation. OBJECTIVE: We examined the association of motor status and treatment benefit by testing patients with a wide range of severity of hemiparesis of the left and right upper extremity. METHOD: Diffusion tensor imaging was performed in 22 patients beyond 12 months after onset of stroke with severe to moderate hemiparesis. Motor function was tested before and after 2 weeks of modified constraint-induced movement therapy. RESULTS: CST integrity, but not lesion volume, correlated with the motor ability measures of the Wolf Motor Function Test and the Motor Activity Log. No differences were found between left and right hemiparesis. Motor performance improved significantly with the treatment regime, and did so equally for patients with left and right arm paresis. However, treatment benefit was not associated with either CST integrity or lesion volume. CONCLUSION: CST integrity correlated best in this small trial with chronic long-term status but not treatment-induced improvements. The CST may play a different role in the mechanisms mediating long-term outcome compared to those underlying practice-induced gains after a chronic plateau in motor function.
Harris JM, Dean PJA (2003) Accuracy and Precision of Binocular 3-D Motion Perception., Journal of Experimental Psychology: Human Perception and Performance 29 (5) pp. 869-881
In principle, information for 3-D motion perception is provided by the differences in position and motion between left- and right-eye images of the world. It is known that observers can precisely judge between different 3-D motion trajectories, but the accuracy of binocular 3-D motion perception has not been studied. The authors measured the accuracy of 3-D motion perception. In 4 different tasks, observers were inaccurate, overestimating trajectory angle, despite consistently choosing similar angles (high precision). Errors did not vary consistently with target distance, as would be expected had inaccuracy been due to misestimates of viewing distance. Observers appeared to rely strongly on the lateral position of the target, almost to the exclusion of the use of depth information. For the present tasks, these data suggest that neither an accurate estimate of 3-D motion direction nor one of passing distance can be obtained using only binocular cues to motion in depth.
Dean P, Sterr A (2012) Long-term effects of mild traumatic brain injury on cognitive performance, BRAIN INJURY 26 (4-5) pp. 395-396
Hope C, Seiss E, Dean PJA, Williams K, Sterr A (2013) Consumption of glucose drinks slows sensorimotor processing: Double-blind placebo-controlled studies with the Eriksen flanker task, Frontiers in Human Neuroscience 7 651 Frontiers
Modulations of blood glucose concentration (BGC) in the normal range are known to facilitate performance in memory and other cognitive tasks but few studies have investigated the effects of BGC variations on complex sensorimotor task so far. The present study aimed to examine glucose effects with the Eriksen flanker task. This task was chosen because it can dissociate between the effects of BGC on sensorimotor processing and cognitive control by assessing congruency effects. In two linked double-blind placebo controlled experiments BGC was elevated within the normal BGC range (4-7 mmol/litre) by approx. 1.5 mmol/litre with glucose drinks and compared to a placebo drink condition while a flanker task with either strong or weak stimulus-response (SR) mapping was performed. Modulation of the performance in the flanker task by glucose was linked to the strength of the SR mapping but not congruency effects. Under weak SR mapping, reaction times (RT) were slowed in the glucose condition compared to placebo while error rates remained unchanged, whereas cognitive control was not affected by glucose. When SR mapping was strong, no differences were found between glucose and placebo. Enhanced glucose levels differentially affect behaviour. Whereas the literature mainly reports facilitating characteristics of enhanced glucose levels in the normal range, the present study shows that higher glucose levels can slow RTs. This suggests that glucose does not have a uniform effect on cognition and that it might be differential depending on the cognitive domain.
Primary objective: To compare the prevalence of persistent post-concussion syndrome (PCS; >1 year post-injury) in participants with mild traumatic brain injury (mTBI) and those without head injury. Research design: A cross-sectional sample of 119 participants with mTBI and 246 without previous head injury. Methods: Online questionnaires collected data about post-concussion symptoms, cognitive failures, anxiety, depression, sleep behaviour and post-traumatic stress disorder. Variability within the sample was addressed by splitting by PCS diagnosis to create four groups: mTBI + PCS, mTBI-PCS, Control + PCS and Control-PCS. PCS was diagnosed using ICD-10 criteria in all groups, with controls not requiring previous head injury. Main outcomes and results: PCS was present to a similar extent in participants with no head injury (34%) compared to those with mTBI (31%). Only report of headaches, which could be caused by expectation bias, distinguished between mTBI + PCS and Control + PCS groups. In addition, significantly higher cognitive problems were observed in participants with mTBI compared with the control group. Conclusions: Persistent PCS, as currently defined, is not specific to mTBI. These data suggest that somatic and cognitive symptoms are most likely to be able to distinguish PCS after mTBI from that present in the general population. Further research is necessary into these factors in order to create more specific PCS diagnostic criteria.
Dean PJ, Tuck VL, Harris JM (2003) Perceived direction of binocular 3-D motion when tracking a moving object, Journal of Vision 3 (9)
Previous research has shown that perception of binocular 3-D object motion can be highly inaccurate (Harris, ECVP 2000, 2001). In these studies, observers were asked to maintain fixation on a stationary point. However, when viewing moving objects in real world situations, the moving object is often followed with the eyes. Are observers able to use information about their eye movements to help determine 3-D object motion? In this study we compared a condition in which observers fixated on a stationary reference point whilst judging 3-D motion direction, with one where they followed the moving object with their eyes. The display always consisted of a pair of stereoscopically presented points (each subtending 8.3 min arc). Observers viewed trajectories ranging from 20 deg to the left of straight ahead, to 20 deg to the right. The perceived trajectory of the moving point was recorded by the observer, for each trial, by moving a pointer to reproduce the angle. The average perceived trajectory angle for each observer, for each angle, was measured. Pooled results from 14 observers showed that very similar angles were perceived for each condition. Performance was highly inaccurate, as we found previously (e.g. angles of 20 deg are perceived, on average as 39 deg). We also tested whether the observer's precision was similar in the two conditions. We found that observers had a tendency to be more precise for the fixation condition rather than the eye movement condition. The results suggest that there is no advantage to looking at either the fixation point or the moving point. The inaccuracies of trajectory perception shown in previous research cannot be improved on (or indeed are not impaired further) by the addition of eye movement information.
Chronic hemiplegia is a common long-term consequence of stroke, and subsequent motor recovery is often incomplete. Neurophysiological studies have focused on motor execution deficits in relatively high functioning patients. Much less is known about the influence exerted by processes related to motor preparation, particularly in patients with poor motor recovery.
The current study investigates motor preparation using a modified response-priming experiment in a large sample of patients (n = 50) with moderate-to-severe chronic hemiparesis. The behavioural results revealed that hemiparetic patients had an increased response-priming effect compared to controls, but that their response times were markedly slower for both hands. Patients also demonstrated significantly enhanced midline late contingent negative variation (CNV) during paretic hand preparation, despite the absence of overall group differences when compared to controls. Furthermore, increased amplitude of the midline CNV correlated with a greater response-priming effect. We propose that these changes might reflect greater anticipated effort to respond in patients, and consequently that advance cueing of motor responses may be of benefit in these individuals. We further observed significantly reduced CNV amplitudes over the lesioned hemisphere in hemiparetic patients compared to controls during non-paretic hand preparation, preparation of both hands and no hand preparation. Two potential explanations for these CNV reductions are discussed: alterations in anticipatory attention or state changes in motor processing, for example an imbalance in inter-hemispheric inhibition.
Overall, this study provides evidence that movement preparation could play a crucial role in hemiparetic motor deficits, and that advance motor cueing may be of benefit in future therapeutic interventions. In addition, it demonstrates the importance of monitoring both the non-paretic and paretic hand after stroke and during therapeutic intervention.
Stroke patients with motor deficits often report daytime sleepiness. While slowing
of the EEG during wakefulness has been shown after stroke, it is unknown if and how
this is linked to their perception of sleepiness. Using waking EEG and a motor task
(associated with mild sleepiness), we examined: 1) differences in the frequency composition
and lateralisation of the EEG between stroke patients and controls, and 2) the
relationship between the EEG and subjective sleepiness ratings. EEG and Karolinska
Sleepiness Scale (KSS) data were collected from 15 right hemispheric stroke patients
and 15 matched controls before and after a motor priming task. Frequency analysis
was performed on C3 and C4 channels. Prior to the task, the stroke group revealed
increased power density below 10 Hz compared to controls for both hemispheres, with
more pronounced effects within the lesioned hemisphere. The motor task significantly
increased KSS scores in both groups. Increased beta and alpha activity was observed
after the task in the control group. The stroke group showed post task increases in beta
activity for the non-affected hemisphere and bilateral increases in alpha and theta activity.
An association between KSS and the EEG was observed post task in the stroke
patients within the theta and alpha bands. Therefore, slowing of the EEG is related to
perception of daytime sleepiness in stroke patients. This effect may not have been
observed in the controls due to the way in which the motor task manipulates sleepiness
within each group, as it is more challenging for those with motor deficits.
Sleepiness is common after stroke, but in contrast to its importance for rehabilitation, existing studies focus primarily on the acute state and often use subjective sleepiness measures only. We used quantitative electroencephalography (qEEG) to extract physiological sleepiness, as well as subjective reports, in response to motor-cognitive demand in stroke patients and controls. We hypothesised that (a) slowing of the EEG is chronically sustained after stroke; (b) increased power in lower frequencies and increased sleepiness are associated; and (c) sleepiness is modulated by motor-cognitive demand. QEEGs were recorded in 32 chronic stroke patients and 20 controls using a Karolinska Drowsiness Test protocol administered before and after a motor priming task. Subjective sleepiness was measured using the Karolinska Sleepiness Scale.The findings showed that power density was significantly increased in delta and theta frequency bands over both hemispheres in patients which were not associated with subjective sleepiness ratings. This effect was not observed in controls.The motor priming task induced differential hemispheric effects with greater increase in low-frequency bands and presumably compensatory increases in higher frequency bands. The results indicate sustained slowing in the qEEG in chronic stroke, but in contrast to healthy controls, these changes are not related to perceived sleepiness.
Harris JM, Dean PJ (2003) Perception of binocular 3-D motion: Visual direction is more important than binocular disparity, Journal of Vision 3 (9)
When an object moves in three dimensions (3-D), a combination of binocular disparity and lateral motion (change in visual direction) can, in principle, be used to determine its direction. We know from previous research that observers can be very poor at judging 3-D direction (e.g. Harris, ECVP, 2000). However, we do not know whether the misperception is due to errors in the processing of visual direction or of binocular disparity. Here we tested how well observers can detect different trajectory angles when disparity, or visual direction, are varied separately. We compared two conditions. In the first, the distance moved in depth by a target (with respect to a stationary reference) was held constant at 27.3 min arc (13.2cm in depth). Trajectory angle was varied by changing the extent of lateral target motion (hence changing the final visual direction of the target), to produce trajectories ranging from straight ahead to 20deg to the left or right of the nose. In the second condition, the lateral distance moved was held constant at 1.2cm to the left or right of straight ahead, and the change in depth of the target was varied to create the same range of trajectory angles. Stimuli were presented stereoscopically using stereo shutter goggles running at 120Hz. When depth was held constant, observers were highly inaccurate at perceiving the trajectory angle, but there was a monotonic relationship between physical and perceived angle: wider physical angles were perceived as wider. However, when visual direction was held constant, many observers perceived the whole range of angles as being very similar. The results suggest that observers may be basing their responses primarily on the visual direction of the target, rather than on the relative extent laterally and in depth. Although in principle disparity and lateral position specify 3-D trajectory angle, in practise the human brain may use very much simpler strategies.
Sterr A, Dean PJA, Mathews S (2006) Ageing in Motor Control: Behavioural and ERP correlates of Motor Priming in the Elderly.,
This pilot study explores the metabolic changes associated with persistent postconcussion syndrome (PCS) after mild traumatic brain injury (mTBI; >12 months after injury) using magnetic resonance spectroscopy. We hypothesized that those mTBI participants with PCS will have larger metabolic differences than those without. Data were collected from mTBI participants with PCS, mTBI participants without PCS and non-head-injured participants (all groups: n=8). Magnetic resonance spectroscopy metabolite profiles within the dorsolateral prefrontal cortex showed a reduced creatine/choline ratio in mTBI patients compared with control participants. This data provides initial evidence for residual metabolic changes in chronic mTBI patients, but there was no conclusive relationship between these metabolic changes and PCS symptom report. Creatine is involved in maintaining energy levels in cells with high or fluctuating energy demand, suggesting that there may be some residual energy impairment in chronic mTBI.
The aim of the research presented is to gain a better understanding of the processes underlying the persistent report of somatic, cognitive and affective symptoms (known as post-concussion syndrome, PCS) after a mild brain injury (mTBI), and to elucidate whether there are any replicable biological factors contributing towards this syndrome. The results demonstrate that although PCS-like symptoms are present to a similar degree in the non-head injured population, individuals with mTBI and persistent PCS have significantly worse working memory, attention and information processing speed performance. Individuals who suffer an MTBI but do not report continued PCS perform these cognitive tasks to the same level as non-head injured controls. Following on from this, the research presented evidence that individuals with greater PCS severity had greater white matter damage, and greater attention related activity during cognitive tasks. Metabolic differences were also observed in the prefrontal cortex of individuals with mTBI, with a reduction in creatine suggesting some residual energy impairment in chronic mTBI. Combining the structural, metabolic and functional MRI data, we suggested that the increased attentional regulation observed during cognitive tasks may be compensating for reduced working memory capacity and a variation in white matter transmission caused by the structural and metabolic changes after injury. This compensation may in turn underlie some PCS symptoms such as fatigue, headache and insomnia. Therefore, the research as a whole suggests that there may be a neurophysiological basis for persistent PCS.
Sato JR, Dean PJA, Vieira G (2014) Methods for Connectivity Analysis in fMRI, In: Sameshima K, Baccala LA (eds.), Methods in Brain Connectivity Inference through Multivariate Time Series Analysis 11 pp. 197-222 CRC Press
The present study explores the link between brain metabolites, PCS symptoms and cognitive ability in participants who have experienced an mTBI. Lactate has been previously been shown to be elevated in acute mTBI (Son, Park et al. 2000), however, 2 month post-incidence lactate levels had returned to normal. The present study suggests that PCS symptoms as well as metabolite abnormalities may persist. More specifically the data provides initial evidence for a link between the elevation of lactate and with severity of long-term PCS following mTBI.
Poster presented in Session: Other Spectroscopy Methodology
Proceedings of the International Society for Magnetic Resonance in Medicine, 18 (2010); p. 937. ISSN 1545-4428. Available at: http://www.ismrm.org/meetings-workshops/2010-annual-meeting-3/
Mathews S, Ainsley Dean PJ, Sterr A (2006) EEG dipole analysis of motor-priming foreperiod activity reveals separate sources for motor and spatial attention components., Clin Neurophysiol 117 (12) pp. 2675-2683
OBJECTIVE: This study employed EEG source localisation procedures to study the contribution of motor preparatory and attentional processing to foreperiod activity in an S1-S2 motor priming task. METHODS: Behavioural and high-density event-related potential (ERP) data were recorded in an S1-S2 priming task where participants responded to S2 with a left or right-hand button press. S1 either provided information about response hand (informative) or ambiguous information (uninformative). RESULTS: Responses were significantly faster in informative trials compared with uninformative trials. Dipole source analysis of foreperiod lateralized ERPs revealed sources of motor preparatory activity in the dorsolateral premotor cortex (PMd) in line with previous work. In addition, two spatial attention components (ADAN, LDAP) were identified with generators in the PMd and occipitotemporal visual areas in the middle temporal (MT) region, respectively. Separation of motor-related and attentional PMd source locations was reliable along the rostral-caudal axis. CONCLUSIONS: The presence of attentional components in a motor priming paradigm supports the premotor theory of attention which suggests a close link between attention and motor preparatory processes. Separation of components in the premotor cortex is in accord with a functional division of PMd into rostral (higher-order processing) and caudal (motor-related processing) areas as suggested by imaging work. SIGNIFICANCE: A prime for response preparation is a trigger for separate, but closely linked, attention-related activity in premotor areas.
Behavioural studies have indicated that response times on complex reaction time
tasks are faster if blood glucose concentrations are slightly elevated above normal
(Donohoe & Benton, 2000). Such tasks involve several cognitive processing stages
but it is not clear which of these stages are speeded after glucose administration. In
order to investigate this problem we have used a double blind repeated measures design
for the administration of glucose and placebo drinks. Participants performed a
Flanker task while EEG was recorded as a physiological measure. More specifically, we
used a Flanker task that required participants to respond to either left or right pointing
central arrows by pressing a left or a right button, respectively. In addition on
each trial there are extra arrows surrounding the central arrow which all either
pointed in the same (congruent condition) or opposite (incongruent condition) direction
as the central arrow or they were lines without an arrow head (neutral condition)
All condition were presented equiprobably. No significant differences between the glucose
and placebo condition were observed in mean reaction times and errors rates.
However the ERP data showed that the N1 amplitude was significantly increased after
glucose administration. This could indicate that stimulus identification is influenced by
glucose administration, as previous researchers have found an increased N1 amplitude
during discriminative feature processing compared to simple detection tasks (Hopf et
al., 2002). In addition, mean reaction times and error rates were analysed separately
for each of the 8 blocks. Differences between drink types were only found for the reaction
times of the first block. Participants who had received glucose during their 1st
session and placebo during the 2nd session, had longer reaction times after glucose
administration compared to placebo. However this effect was not found for participants
who received placebo before glucose drinks. These findings might be linked to
task difficulty effects. Previous research has shown that high task difficulty is necessary
to find glucose enhancement effects on the Hick task (sensorimotor function;
Donohoe & Benton, 2000), working memory (Kennedy & Scholey, 2001) and episodic
memory (Sünram-Lea et al., 2002). Our results conflict directly with Donohoe and
Benton?s (2000), potentially caused by methodological or task differences. It might be
also possible that separate cognitive processes might be d
Mathews S, Dean PJA, Harrison N, Williams N, Sterr A (2005) Movement preparation and execution following a no-response pre-cue: A pilot study using behavioural and EEG data.,
Hope C, Seiss E, Dean P, Sterr A (2009) An electrophysiological investigation of glucose administration effects on movement preparation and execution, Psychophysiology. Special Issue: Society for Psychophysiological Research Abstracts for the Forty-Ninth Annual Meeting 46 (Supplement s1) Wiley-Blackwell
Behavioural studies suggest that elevated blood glucose concentrations accelerate response
times in complex tasks (Owens and Benton, 2004, Neuropsychobiology). With
the present study we aimed to explore the mechanisms subserving elevated blood glucose
effects (7 mmol/litre versus fasting levels of 5 mmol/litre) by studying EEG-derived
indices of sensorimotor processing. More specifically, the Eriksen flanker task was used
to examine glucose-dependent modulations of the P300, the stimulus lateralized readiness
potentials (LRPs), and response-locked LRP, to see whether enhanced blood glucose
levels affect stimulus evaluation, response planning, and response selection
respectively. 10 participants took part in a within-participant double-blind 2-session
experiment where either glucose (25 g) or placebo drinks were administered. Initial data
suggests slower reaction times, higher error rates and delayed stimulus-locked LRP
onset in incongruent compared to congruent and neutral trials. With placebo administration error rates were increased for the non-dominant hand but not the dominant
hand; no effects were found for the EEG parameters. This suggests that hyperglycaemia
does not affect senorimotor processing in the flanker task. However, the placebo-related
increase in error rates together with the findings of (Donohoe and Benton, 2000) support
the proposition that beneficial effects of increased blood glucose levels on cognition
might only occur when cognitive demands are high.
Encke M, Dean PJA, Seiss E, Sterr A (2013) Effects of aging on motor preparation processes, Psychophysiology 50 (S1) pp. S87-S87 Wiley-Blackwell
The last-in first-out theory suggests that late-maturing brain regions are affected earlier in the life span than those maturing early. Maturation of the motor system and the frontal executive control system continues into early adulthood. Evidence further suggests that motor preparation, index by the contingent negative variation (CNV), matures relatively late in adolescence and is compromised in persons aged 68?83 years. With the present study we explored the progression of age-related changes in motor preparation control by contrasting behavioral and CNV effects in young (18?23), middle-aged (33?44) and older (61?72) persons using a modified response priming paradigm. All three groups showed the typical motor priming effect pattern with faster RTs in valid trials compared to invalid trials. RTs were significantly slower in the older than the middle-aged and young groups, with no significant difference in error rates. A significantly larger CNV validity effect was found for the young group compared to the older group. CNV topography shifted from parietal to more frontal regions with age. These data provide initial evidence for early changes in motor preparation control mechanisms and lend support for the last-in first-out hypothesis.
Dean P, Sato JR, Sterr A (2012) The relationship between structural changes in mTBI and persistent PCS: DTI and cortical thickness analysis, Brain Injury 26 (4-5) pp. 509-509 Informa Healthcare
Mild traumatic brain injury (mTBI) can induce
persistent somatic, affective and cognitive symptoms,
collectively known as post-concussion syndrome
(PCS). It is debated whether this syndrome is
due to biological or psychological factors. Standard
structural imaging only detects lesions in a small
proportion of those with mTBI, and these lesions are
not associated with PCS in the acute (
or chronic (> 3 months) stage. However, microlesions
and diffuse axonal injury (DAI) have been
observed using novel imaging techniques such as
diffusion tensor imaging (DTI). White matter
damage examined in acute and post-acute/chronic
mTBI has been correlated with cognitive and
behavioural measures, as well as outcome from
injury. Increased damage within the white matter
tracts of the corpus callosum and thalamic radiations
is observed in those with poorer outcome at 3
months, whereas grey matter damage is independent
of outcome. This present study aims to investigate
the relation of structural changes and long-term
consequences in more detail by assessing the correlation
between DTI-based indices and persistent
PCS symptomatology. Structural changes were
investigated in participants with chronic (>1 year)
mTBI and persistent PCS (n¼10), participants with
mTBI and no on-going PCS (n¼8) and non-head
injured controls (n¼10). Fractional Anisotropy (FA)
and cortical thickness were compared between
groups to assess white matter integrity and focal
damage respectively. In addition, the association
between neural structure and level of PCS symptom
report was evaluated. We hypothesised that long
fibre white matter bundles, such as the corpus
callosum, would be damaged in participants with
chronic mTBI, with cortical thinning around these
areas. Furthermore, we hypothesised that this
damage would be related to the persistent PCS
symptoms seen after mTBI. If PCS has a biological
basis, then participants with mTBI and persistent
PCS may have sustained greater damage to these areas at the time of injury than participants without
ongoing symptoms. Preliminary analysis demonstrates
a reduction in cortical thickness and white
matter integrity in participants with chronic (>1
year) mTBI, independent of PCS, compared to
controls. Diminished cortical thickness and white
matter integrity were seen for cingulate cortex and
corpus callosum. In addition, similar reductions
were observed when comparing mTBI participants
without PCS to those with PCS. This suggests that
persistent PCS m
OBJECTIVES: Mild traumatic brain injury (mTBI) is a heterogeneous injury, and it is difficult to predict those that will go on to experience sustained post-concussion syndrome (PCS, >3mths). As such, data from a wide variety of sources would be useful in investigating long term outcome, preferably within the same population. This study explored the interplay between functional, structural and metabolic changes after mTBI and their relationship with persistent PCS and cognitive performance. METHODS: fMRI, DTI and MRS data were acquired from participants with chronic (>1 year) mTBI and persistent PCS (n=8), participants with mTBI but no on-going PCS (n=8) and non-head injured controls (n=9). Functional data was acquired whilst participants undertook an n-Back and Paced Serial Visual Addition Task (PVSAT). Conventional analysis was undertaken to investigate areas of difference in BOLD response and fractional anisotropy (FA) between groups. These regions of interest were then used to extract individual BOLD contrast values or FA for each participant. MRS acquired from right DLPFC was analysed. Metabolites which differed between groups were used in further analysis. The relationship between functional, structural and metabolic indices was investigated using partial correlation, controlling the effect of age. RESULTS: Participants with mTBI and PCS displayed less of an increase in BOLD response in prefrontal (left inferior/middle frontal gyrus; PVSAT) and temporal (right medial/inferior temporal lobe; n-Back) areas when performing the most difficult task compared to controls, despite similar task performance in both groups. Greater post-concussion symptom report correlated with reduced temporal (right medial/inferior temporal; n-Back) and posterior cingulate/precuneus (PVSAT) BOLD response, as well as increased anterior cingulate (n-Back) BOLD response. Correlations revealed that reduced BOLD response in the left inferior/middle frontal gyrus also was associated with reduced FA in posterior corpus callosum (r=0.4, p
Dean PJA, Sterr A (2010) Post concussion syndrome without head injury?
A survey study, Brain Injury 3 (24) pp. 423-423
Objectives: According to ICD-10 or DSM-IV criteria Post-Concussion Syndrome (PCS) requires a prior mild traumatic brain injury (mTBI). However, PCS symptoms are non-specific and can also affect non- mTBI populations. Symptoms further overlap with other diagnoses, such as depression. Consequently, the degree to which PCS is specific to or caused by mTBI is still debated. With the present study we aim to investigate the nature of PCS in greater detail by looking whether PCS is specific to mTBI, and the extent to which these symptoms and related factors (depression, anxiety,daytime sleepiness and cognitive failures) exist in the non-mTBI population. Method: An online survey was sent to University staff and students. Included in this survey were the Rivermead Post Concussion Questionnaire (RPQ), Cognitive Failures Questionnaire (CFQ), Hospital Anxiety and Depression Scale (HADS), Epworth Sleepiness Scale (ESS), along with demographic questions and those related to the mTBI sustained. PCS was diagnosed as 3 or more symptoms within DSM-IV criteria. Results: The survey created a database of 375 entries, 127 for mTBI and 248 controls (no history of mTBI). Within these groups the proportion of individuals experiencing PCS symptoms was not statistically different (39% for mTBI, 32% for control; Chi squared p¼0.2), and there was no group difference for the RPQ, HADS or ESS. However, respondents with a history of mTBI showed significantly higher CFQ scores (p
greater scores for all questionnaires p
had greater scores for the RPQ, CFQ and HADS
than both groups without PCS (p
was only one difference when comparing the two
groups with mTBI to those without (CFQ: mTBI+PCS greater than Control+PCS (p
and without brain injury. Data on depression,
anxiety, cognitive failures and daytime sleepiness scores show no increase in those with mTBI, but are significantly higher in those with PCS. Analysis of the four subgroups revealed no interaction between mTBI and PCS. This suggests that PCS is
CI therapy is effective in patients with relatively good levels of residual arm function but its applicability to patients with low-functioning hemiparesis is not entirely clear. In the present study, we examined the feasibility and efficacy of the CI therapy concept in patients with very limited upper arm function prior to treatment, and further tested how the length of daily shaping training and constraining the good arm affects treatment outcome. In a baseline-controlled design, 65 chronic patients were treated with 2weeks of modified CI therapy. Patients were randomly allocated to four treatment groups receiving 90 or 180 min of daily shaping training applied with or without constraint, respectively. Outcome
was measured through the Reliable Change Index, which was calculated for parameters of motor function, health, and psychological wellbeing. Follow-up data were collected at 6 and 12 months.Two analyses were conducted, a whole-group analysis across all 65 participants
and a sub-group analysis contrasting the four treatment variants. The whole-group analysis showed a significant treatment effect, which was largely sustained after 1 year. The sub-group analysis revealed a mixed picture; while improvements against the baseline period were observed in all four subgroups, 180 min of daily shaping training coupled with the constraint yielded better outcome on the MAL but not the WMFT, while for 90 min of training the level of improvement was similar for those who wore the constraint and those who did not. Together these results suggest that, at least in those patients available for follow-up measures, modified CI therapy induces sustained improvements in motor
function in patients with chronic low-functioning hemiparesis. The absence of clear differences between the four treatment variants points to a complex relationship between the length of daily shaping training and the constraint in this patient group, which is likely to be mediated by fatigue and/or compliance with the constraint.
Pinaya WHL, Fraga FJ, Haratz SS, Dean PJA, Conforto AB, Bor-Seng-Shu E, Teixeira MJ, Sato JR (2015) Comparing Methods for Determining Motor-Hand Lateralization Based on fTCD Signals, Journal of Medical Systems 39 (2) pp. 185-193
The lateralization index (LI) as determined from
functional transcranial Doppler sonography (fTCD) can be used to determine the hemispheric organization of neural activation during a behavioral task. Previous studies have proposed different methods to determine this index, but to our knowledge no studies have compared the performance of these methods. In this study, we compare two established methods with a simpler method proposed here. The aim was to see whether similar results could be achieved with a simpler
method and to give an indication of the analysis steps required to determine the LI. A simple unimanual motor task was performed while fTCD was acquired, and the LI determined by each of these methods was compared. In addition, LI determined by each method was related to behavioural output in the form of degree of handedness. The results suggest that although the methods differed in complexity, they yielded
similar results when determining the lateralization of motor functions, and its correlation with behavior. Further investigation
is needed to expand the conclusions of this preliminary study, however the new method proposed in the paper has great potential as it is much simpler than the more established methods yet yields similar results.
To investigate sustained structural changes in the long-term (>1 year) after mild traumatic brain injury (mTBI) and their relationship to ongoing post-concussion syndrome (PCS).Morphological and structural connectivity magnetic resonance imaging (MRI) data were acquired from 16 participants with mTBI and nine participants without previous head injury.Participants with mTBI had less prefrontal grey matter and lower fractional anisotropy (FA) in the anterior corona radiata and internal capsule. Furthermore, PCS severity was associated with less parietal lobe grey matter and lower FA in the corpus callosum.There is evidence for both white and grey matter damage in participants with mTBI over 1 year after injury. Furthermore, these structural changes are greater in those that report more PCS symptoms, suggesting a neurophysiological basis for these persistent symptoms.
Dean P, Minarik T, Opitz B, Sterr A (2016) Functional correlates of creatine supplementation, BRAIN INJURY 30 (5-6) pp. 663-663 TAYLOR & FRANCIS INC
The neural simulation theory predicts similarity for the neural mechanisms subserving overt (motor execution) and covert (movement imagination) actions. Here we tested this prediction for movement preparation, a key characteristic of motor cognition.
High-density electroencephalogram (EEG) was recorded during covert and overt actions. Movement preparation was studied with a motor priming paradigm, which varied task complexity and amount of advance information. Participants performed simple or complex sequential finger movements either overtly or covertly. Advance information was either fully predictive or partially predictive. Stimulus-locked event-related potential (ERP) data showed the typical pattern of foreperiod activation for overt and covert movements. The foreperiod contingent negative variation (CNV) differed between simple and complex movements only in the execution task. ERP topographies differed between execution and imagination only when advance information was fully predictive.
Results suggest a differential contribution of the movement preparation network to action imagination and execution. Overt and covert actions seem to involve similar though not identical mechanisms, where overt actions engage a more fine-grained modulation of covert preparatory states.
Mathews S, Dean PJA, Sterr A (2006) Seperating spatial attention and motor-related lateralized ERP components in an S1-S2 motor priming paradigm,
Dean PJA, McNamara A, Vieira G, Sato J, Sterr A (2013) Structural and functional changes in mTBI and their relationship to persistent PCS: DTI, cortical
thickness and fMRI analysis., British Neurosci. Assoc. Abstr. 22 pp. 892-892
Mild traumatic brain injury (mTBI) can induce persistent somatic, affective and cognitive symptoms, collectively
known as post-concussion syndrome (PCS). Standard structural imaging only detects lesions in a small
proportion of those with mTBI, and these lesions are not associated with PCS. However, subtle changes in
structure have been observed with imaging techniques such as diffusion tensor imaging (DTI). Furthermore,
these changes have been shown to correlate with cognitive and behavioural outcome in mTBI participants. This
study aims to further this research by investigating the relationship between changes in neural structure and
function, cognitive outcome and PCS symptomatology in the long term (>1 year) after mTBI.
DTI and functional magnetic resonance imaging (fMRI) data were acquired from participants with chronic (>1
year) mTBI and persistent PCS (n=10), participants with mTBI and no on-going PCS (n=8) and non-head injured
controls (n=10). Fractional Anisotropy (FA) and cortical thickness were calculated from DTI and standard
structural data acquisitions. Two cognitive tasks were presented to participants in the fMRI study, one assessing
working memory (n-Back) and the other assessing information processing speed (paced visual serial addition
task [PVSAT]). We hypothesised that participants with mTBI would show greater structural damage and larger
BOLD response during the cognitive tasks. In addition, these changes should be related to the persistent PCS symptoms reported.
Preliminary analysis demonstrates a reduction in cortical (cingulate, frontal and temporal cortex) and white matter
(corpus callosum, internal capsule) integrity in participants with mTBI compared to controls. Reductions in similar
areas were associated with higher PCS symptom report (figure A and B). The fMRI analysis revealed little
difference between groups for the n-Back, but evidence of increased prefrontal activity (figure C) in participants
with mTBI and persistent PCS during PVSAT performance. This early analysis supports the hypothesis that
persistent PCS symptoms may have a biological element, with those reporting greater symptoms having greater structural damage and functional changes.
Although a proportion of individuals report chronic cognitive difficulties after mild traumatic brain injury (mTBI), results from behavioral testing have been inconsistent. In fact, the variability inherent to the mTBI population may be masking subtle cognitive deficits. We hypothesized that this variability could be reduced by accounting for post-concussion syndrome (PCS) in the sample. Thirty-six participants with mTBI (>1 year post-injury) and 36 non-head injured controls performed information processing speed (Paced Visual Serial Addition Task, PVSAT) and working memory (n-Back) tasks. Both groups were split by PCS diagnosis (4 groups, all n = 18), with categorization of controls based on symptom report. Participants with mTBI and persistent PCS had significantly greater error rates on both the n-Back and PVSAT, at every difficulty level except 0-Back (used as a test of performance validity). There was no difference between any of the other groups. Therefore, a cognitive deficit can be observed in mTBI participants, even 1 year after injury. Correlations between cognitive performance and symptoms were only observed for mTBI participants, with worse performance correlating with lower sleep quality, in addition to a medium effect size association (falling short of statistical significance) with higher PCS symptoms, post-traumatic stress disorder (PTSD), and anxiety. These results suggest that the reduction in cognitive performance is not due to greater symptom report itself, but is associated to some extent with the initial injury. Furthermore, the results validate the utility of our participant grouping, and demonstrate its potential to reduce the variability observed in previous studies.
Background: Persistent postconcussion syndrome (PCS) occurs in around 5? 10% of individuals after mild traumatic brain injury (mTBI), but research into the underlying biology of these ongoing symptoms is limited and inconsistent. One reason for this could be the heterogeneity inherent to mTBI, with individualized injury mechanisms and psychological factors. A multimodal imaging study may be able to characterize the injury better. Aim: To look at the relationship between functional (fMRI), structural (diffusion tensor imaging), and metabolic (magnetic resonance spectroscopy) data in the same participants in the long term (>1 year) after injury. It was hypothesized that only those mTBI participants with persistent PCS would show functional changes, and that these changes would be related to reduced structural integrity and altered metabolite concentrations. Methods: Functional changes associated with persistent PCS after mTBI (>1 year postinjury) were investigated in participants with and without PCS (both n = 8) and non-head injured participants (n = 9) during performance of working memory and attention/processing speed tasks. Correlation analyses were performed to look at the relationship between the functional data and structural and metabolic alterations in the same participants. Results: There were no behavioral differences between the groups, but participants with greater PCS symptoms exhibited greater activation in attention-related areas (anterior cingulate), along with reduced activation in temporal, default mode network, and working memory areas (left prefrontal) as cognitive load was increased from the easiest to the most difficult task. Functional changes in these areas correlated with reduced structural integrity in corpus callosum and anterior white matter, and reduced creatine concentration in right dorsolateral prefrontal cortex. Conclusion: These data suggest that the top-down attentional regulation and deactivation of task-irrelevant areas may be compensating for the reduction in working memory capacity and variation in white matter transmission caused by the structural and metabolic changes after injury. This may in turn be contributing to secondary PCS symptoms such as fatigue and headache. Further research is required using multimodal data to investigate the mechanisms of injury after mTBI, but also to aid individualized diagnosis and prognosis.
Driven by considerations arising from studies in hemiplegic patients, we examined how the insertion of rare n-response trials affects motor preparation studied in S1-S2 paradigms. Results for the motor priming task (experiment 1) showed that for response-requiring conditions the 'validity effect' was conserved for behavioural and ERP indices. For the no-response condition, foreperiod activities were similar to neutral trials suggesting motor preparation in both conditions and hence preparation for the unlikely event. A second experiment with fully predictive primes showed no evidence for movement preparation processes in no-response trials. These findings suggest different strategies for the anticipation of likely responses compared to likely events that don't require a response.
There is significant overlap between the neuropathology of mild traumatic brain injury (mTBI) and the cellular role of creatine, as well as evidence of neural creatine alterations after mTBI. Creatine supplementation has not been researched in mTBI, but shows some potential as a neuroprotective when administered prior to or after TBI. Consistent with creatine?s cellular role, supplementation reduced neuronal damage, protected against the effects of cellular energy crisis and improved cognitive and somatic symptoms. A variety of factors influencing the efficacy of creatine supplementation are highlighted, as well as avenues for future research into the potential of supplementation as an intervention for mTBI. In particular, the slow neural uptake of creatine may mean that greater effects are achieved by pre-emptive supplementation in at-risk groups.
Emotions play a pivotal role in guiding our behaviour within society and our environment. In particular, emotions enable interpersonal social interactions through non-verbal communication that may be below conscious awareness. However, when there is some disruption to normal emotional processing, such as in anxiety disorders, quality of life of the individual can be severely disrupted. Anxiety disorders account for nearly a quarter of all mental health diagnoses, however the aetiology and underpinning neural correlates of anxiety
are still not fully understood. This thesis sought to investigate the neurobiological mechanisms of emotion processing, specifically in the amygdala, in a healthy sub-clinical cohort. Six different studies are presented using quantitative methodology to explore amygdala activation and connectivity during emotion processing, and structural differences, as modulated by gender and sub-clinical anxiety. Overall results reveal a modulating effect of sub-clinical anxiety on amygdala habituation, fronto-amygdala connectivity (at rest and during emotion processing) and neural structure. In addition, results presented in this thesis suggest that there may be an attentional component to characteristic hyper-responsivity of the amygdala during emotion processing seen in clinical anxiety patients that should be
incorporated into future models of maladaptive emotion. Furthermore, various different chapters in this thesis present evidence that the left amygdala appears to be more specialised for responses to more socially salient stimuli and the right amygdala appears to be more
responsive to threat related stimuli indicating that key theoretical models of emotion (the dual processing model, and the salience detection model) should be integrated into one cohesive model of emotion processing. In addition to these theoretical implications, results
demonstrating the modulating effect of anxiety and gender presented in this thesis suggest that research on emotion should account for individual differences as a matter of standard practice. This thesis also supports the use of resting state -functional magnetic resonance
imaging (fMRI) as a low cost, valid alternative, to task based fMRI within the study of anxiety. Finally, results suggest that investigation of structural differences in sub-clinical populations, and the use of analytical methods such machine learning classification
techniques, could aid the development of diagnostic tools that can
Transcranial direct current stimulation (tDCS) as a means for enhancing learning and memory has received a lot of attention in recent times. However, its applicability in a wider context has been limited due to lack of replicability across the literature. This may likely stem from inter-individual differences such as age, gender, nutrition, stress, brain morphology and sleep. Sleep in particular may be a source of inter-individual differences in tDCS-effect because of its link to brain plasticity mechanism such as long-term potentiation (LTP). The extent to which sleep may account for inter-individual differences in tDCS outcomes has not been assessed in the literature. Therefore, the central aim of this thesis is to investigate 1) the effect of sleep quality 2) circadian mis- /alignment 3) prior sleep compared to wake on tDCS-enhanced learning. Findings from this thesis suggests that sleep quality does not affect variability in tDCS-effect on cognitive performance, while circadian mis/-alignment and prior wakefulness before task may modulate tDCS-efficacy. In conclusion, data suggests that tDCS-effect is greater in a brain which is in a non-optimal state in terms of circadian misalignment and prolonged wake, and in this context, sleep may be responsible for variabilities in tDCS studies. These findings have implications for researchers and clinicians using tDCS. Further studies are required to fully characterise the findings from this thesis.
Physical load carriage is an essential duty for military personnel. Physical load carriage induces psychological and physiological effects, but the influence of load carriage on brain activity and subsequent cognitive performance is largely unknown. This due to difficulties in disentangling the subtle behavioural effects under load carriage in complex occupational settings. To investigate how load carriage influences cognition directly, continuous measures of brain activity must be obtained in realistic settings. Mobile EEG is ideally suited to this task.
Across four studies, mobile EEG recordings were used to assess to what extent load carriage influences attention. Four objectives were defined. 1. To evaluate mobile EEG as a viable tool in real-life settings (studies 1-4). 2. Investigate the influence of walking on attentional processes (study 1, selective attention; study 2, change detection). 3. Establish the impact of load carriage on brain activity during walking (study 3). 4. Assess the interaction of load carriage on attentional processes during walking (study 4). Interpretations of resulting data were conceptualised in the proposed dynamic resource allocation model of cognitive performance.
Successful application of Mobile EEG was evident and found signal quality comparable to EEG recorded in a laboratory. Moreover, walking influenced attentional processes in an indirect way, moderated by the environment and concurrent perceptual load. While a steady state neural index of walking was recorded in a natural setting, this was invulnerable to load carriage effects. Further, and most pressing for this thesis, load carriage had little influence on neural indices of attention. Despite this, there is some indication from the data that fatigue plays a prominent role in the interaction of load carriage and cognitive function, and further exploring the neural underpinnings of motivation may prove fruitful in future studies of load carriage and cognitive function.
Presenting information in a coherent fashion has been shown to increase processing fluency, which in turn influences affective responses. The pattern of responses have been explained by two apparently competing accounts: hedonic marking (response to fluency is positive) and fluency amplification (response to fluency can be positive or negative, depending on stimuli valence). This paper proposes that these accounts are not competing explanations, but separate mechanisms, serving different purposes. Therefore, their individual contributions to overall affective responses should be observable. In three experiments, participants were presented with businesses scenarios, with riskiness (valence) and coherence (fluency) manipulated, and affective responses recorded. Results suggested that increasing the fluency of stimuli increases positive affect. If the stimulus is negative, then increasing fluency simultaneously increases negative affect. These affective responses appeared to cancel each other out (Experiment 1) when measured using self-report bipolar scales. However, separate measurement of positive and negative affect, either using unipolar scales (Experiment 2) or using facial electromyography (Experiment 3), provided evidence for co-occurring positive and negative affective responses, and therefore the co-existence of hedonic marking and fluency amplification mechanisms.
Processing fluency has been shown to be flexible metacognitive cue for a range of judgements including truth, familiarity, and trust. Amongst these, affect judgements are of particular interest as 1) affect can be genuinely evoked by fluency, and 2) affect can be used as a cue for other judgements. However, there is disagreement towards the pattern of affective responses arising from fluency. The hedonic marking hypothesis (Winkielman, Schwarz, Fazendeiro, & Reber, 2003) suggests that fluency is fundamentally positive, whilst the fluency amplification account (Albrecht & Carbon, 2014) suggests that the affective response can be positive or negative, depending on (and congruent with) the valence of stimuli being exposed to. Whilst these accounts have been used as competing explanations, this thesis argues that they both contribute to overall affective responses in a novel multi-source account.
This thesis developed a novel set of business scenarios to manipulate fluency (using coherence) and valence (using risk). Evidence from three approaches is presented: 1) Meta-Analysis examining affective responses to fluency, with a sample of 108 publications (k = 591 effect sizes), 2) Five behavioural experiments, and 3) Facial electromyography (fEMG). Across these approaches, neither hedonic marking nor fluency amplification in isolation could account for the full pattern of results. Instead, results were explained by the combined contribution of the two models, as predicted by the multi-source account. The unique findings were uncovered by manipulating stimuli valence, as well as separately measuring positive and negative affect, an approach not previously investigated in the literature, thereby adding methodological, as well as theoretical, contributions to the literature on fluency effects. Implications for future research are to adopt a separate measurement approach to investigate wider judgement domains, whilst practical implications for business assessment and agenda setting are also discussed.