Local and Global Dynamics of Neuronal Activity in the Neocortex: Implications for the Function of Sleep
Departmental Seminar
- When?
- Wednesday 6 February 2013, 14:15 to 15:15
- Where?
- 39 BB 02
- Open to:
- Alumni, Public, Staff, Students
- Speaker:
- Dr Vladyslav Vyazovskiy, Lecturer in Sleep and Chronobiology, FHMS, University of Surrey
In the last decades a vast empirical and theoretical knowledge about sleep mechanisms has been accumulated. Surprisingly, the function of sleep still remains elusive. Moreover, the question of “why do we sleep?” is now being gradually replaced with a more fundamental one: “what is sleep?” The basic problem with defining sleep is that on one hand it is a state, inasmuch as it is different from other states, such as wakefulness, and on the other hand it is a process, since it is not static, but evolves in time and space in a highly complex manner. There are multiple temporal scales relevant for sleep process – starting from a fast millisecond scale of individual neuron spiking, that changes depending on whether the animal is awake or asleep, and up to a scale of hours or even days, at which the overall amount and architecture of sleep is regulated. With respect to spatial scales sleep also shows astounding complexity – indeed, it is associated with characteristic changes at levels as remote from each other as an individual neuron and the whole brain. Understanding the mechanisms underlying spatio-temporal dynamics of sleep will help us to understand not only what sleep is, but also why it is necessary.
Biography
Dr Vyazovskiy was appointed as a Lecturer in Sleep and Chronobiology at the University of Surrey February 2012. He has received training in leading laboratories in the field: the Sleep and Chronobiology Laboratory, University of Zurich, Switzerland (Professors A.A. Borbèly and I. Tobler) and the Sleep and Consciousness Laboratory, University of Wisconsin-Madison, USA (Professors G Tononi and C Cirelli). The work of the applicant has been devoted to elucidating cortical neuronal and network mechanisms of sleep regulation. The most relevant work is his recent publication in Nature (Vyazovskiy et al., 2011), in which he and colleagues reported that following sleep deprivation cortical neurons in awake freely moving rats tend to go briefly ‘OFF line’ as they do in sleep, and that such “local sleep” was associated with an impairment in a behavioural task. This study provided the most appealing evidence yet for a currently highly influential view that sleep is a property of local neuronal assemblies, has a role in synaptic plasticity, and affects cognition (Krueger and Tononi, 2011).
The study reported in Nature was a logical continuation of his earlier work in which he addressed the cellular mechanisms of sleep homeostasis by performing extracellular multi- and single-unit recordings from the neocortex of awake and sleeping rats. Specifically, his work showed that the pattern of neuronal activity in the neocortex is determined by preceding sleep/wake history. The results of this pioneering study were published in Neuron (2009). This work was preceded by his early studies showing how specific sensory stimulation led to changes in sleep that were confined to those brain areas most affected by sensory stimulation (Vyazovskiy et al., J Sleep Res, 2000). This publication triggered a long series of studies performed in many laboratories around the world aimed at understanding the mechanisms underlying local sleep regulation in animals and humans. During his postdoctoral studies, he led the effort in providing comprehensive experimental evidence for investigating synaptic mechanisms of sleep homeostasis. This work, published in Nature Neuroscience, J Neuroscience, Cerebral Cortex and Sleep provided conclusive evidence in support of the hypothesis that being awake is associated with increased cortical effective connectivity (Tononi and Cirelli, 2006). Finally, he and colleagues have also performed a challenging experiment, which demonstrated that in chronically sleep-deprived rats, slower EEG activity, including SWA (0.5–4 Hz) or low theta (5–7 Hz) activity, leaks into periods of behavioural waking, and it does so in a region-specific manner (Vyazovskiy, Leemburg et al,. PNAS, 2009). This experiment contributed to our understanding of the mechanisms of cognitive impairments typical under chronic sleep loss conditions experienced by many people living in modern societies.