Professor of Sleep Physiology
- Director of Graduate Studies
Our knowledge about sleep has grown exponentially in the last decades, but strikingly it did not bring us closer to understanding of what sleep is about in the first place. There is no theory of sleep yet, and this is an important gap to be filled. Sleep requires special treatment because it is unlike many other phenomena where the research subject is well defined, and there is language to describe it.
What is sleep then? By and large, sleep and wakefulness are defined by the strength and directionality of our interaction with the environment. When we wake up, we become aware of the outside world, it comes into being for us, and, at the same time, we start acting upon the surrounding, physically or mentally. On the contrary, when we fall asleep, the surrounding stops existing for us, but also we stop existing from the world’s vantage view. Sleep is a relational process – between organisms and the world around, and it is elusive, as it is typically defined in terms of what it is not, rather than what it is.
The central question we are trying to tackle is "Why do we sleep?", where "why" is of two kinds. First, we are studying the "mechanisms" that regulate our sleep, and make it happen: “how come we sleep?” or “why we sleep in that particular way?” Our traditional understanding is that we are programmed to perform a certain amount of sleep each day, but the nature of the time-keeping mechanism that tracks time spent awake and asleep is unknown. The other “why” is the biological purpose of sleep, where sleep is often viewed as a vital need. "Sleep need" is a somewhat misleading concept, as there are striking examples from the animal kingdom where animals can easily change their sleep amount drastically, depending on other ecological needs, and without noticeable negative consequences.
What is the meaningful level of biological organisation that is relevant for understanding what sleep is? Is sleep merely a side-effect and unwanted consequence of our daily wakeful activities? Is it, as some of our colleagues put it, the price to pay for our waking life? Or is it our basal, default state of being, from which we emerge only to satisfy our vital physiological needs before going back to it?
One theory suggests that sleep is not a state of the whole organism, but sleep originates at the level of local neural networks and is ultimately a response to their activity or “use” during wakefulness. We are working on the provocative idea of “local sleep”, according to which we are never fully awake or fully asleep. Perhaps sleep is as an emergent property, which ultimately arises from the concerted behaviour of individual cells, interconnected with each other in highly complex networks?
Sleep is just one of many ordinary and non-ordinary states of being – from pathological to entirely normal yet unusual – and one way to understand sleep is through comparing it with other states. For example, we are interested in understanding the origin of altered states, induced by psychedelics, or neurophysiology and function of torpor and hibernation. Hibernating animals appear to be sleeping, yet it is a very different state, defined based on reduced metabolism, rather than altered behaviour and sensory responsiveness. Intriguingly, studies suggest that sleep is a gateway to the state of torpor, yet animals emerging from torpor manifest increasing sleep drive, for reasons we do not understand.
In collaboration with other groups at DPAG, Kavli Institute for Nanocience Discovery and beyond, we use and develop a variety of models, methodologies and approaches - from signal analysis and cortical and subcortical stimulation or silencing, ageing, cutting-edge transgenic and viral tools or behaviour, to mathematical modelling, circadian manipulations, sleep phenotyping and pharmacology.
Effects of clozapine-N-oxide and compound 21 on sleep in laboratory mice.
Traut J. et al, (2023), Elife, 12
Detection of neuronal OFF periods as low amplitude neural activity segments.
Harding CD. et al, (2023), BMC Neurosci, 24
Intracellular chloride regulation mediates local sleep pressure in the cortex.
Alfonsa H. et al, (2022), Nat Neurosci
Tinnitus: at a crossroad between phantom perception and sleep
MILINSKI L. et al, (2022), Brain Communications
Human lesions and animal studies links the claustrum to perception, salience, sleep, and pain.
Atilgan H. et al, (2022), Brain