While these animals largely exhibit normal wake behaviours, we now describe how their brain activity is entirely altered, as manifested in prolonged periods of complete neuronal silence, especially apparent during sleep. Such patterns of brain activity, dominated by burst suppression was previously described in an immature brain, deafferented cortical slabs, coma or deep anaesthesia, but never during normal physiological sleep. The research team provides a detailed characterisation of sleep and cortical activity in these animals, using a variety of approaches – from sleep deprivation and sensory stimulation, to mathematical modelling.
Most importantly, these findings represent a paradigm shift in the way states of vigilance and consciousness are classified. Previous literature has focused on an ever-increasing number of specific cell populations or brain subregions, which are thought to control the switch between well-defined states, but this new work suggests that state control is more nuanced.
Professor Vyazovskiy comments, ''For decades, the field has focused on finding the key sleep- or wake-promoting circuit (or "switch"), but the possibility that states are controlled in a global manner has been overlooked. We now propose a unifying model, whereby the emphasis is shifted to the role of varying levels of global network excitability. Specifically, we propose that vigilance states – both spontaneous and induced, such as anaesthesia – are not mutually exclusive phenomena with unambiguous boundaries, but represent a continuum determined by the level of network excitability, which is critical for both state-dependent neuronal oscillations and behaviour. We posit that a finely tuned global neuronal excitability allows the brain to transition quickly and seamlessly between a variety of states, around a default sleep-like state to which network activity always gravitates in the absence of stimulation.'
Read the full story on the Department of Physiology, Anatomy and Genetics website.