What really makes the field of sleep research so exciting is that we still do not know what sleep is for. We know why we eat, why we drink and why we breathe, but we spend one third of our life asleep, sacrificing all wakeful activities, and we still do not know why we have to do it. - Associate Professor Vladyslav Vyazovskiy
"Current Opinion in Physiology" publishes invited reviews that reflect and shape current opinion on physiology and its future directions. In a special issue focusing on the physiology of sleep, editors Associate Professor Vladyslav Vyazovskiy and Professor A. Jennifer Morton approach the core question of 'why do we sleep' from two distinct angles; 'how come', the neurobiology and mechanisms behind sleep, and 'what for', the biological purpose of sleep. According to Prof Vyazovskiy: "One approach we can take is to first understand 'how come' we sleep, basically dissect the necessary ingredients of the sleep process, and this may help us to address the 'what for' question."
To address these questions, they have invited researchers from a wide range of disciplines within sleep research, including several early career researchers in a bid to bring fresh opinions to the debate and ultimately move the field forward. Prof Vyazovskiy says: "Why we are still grappling with the question 'why do we sleep?' Maybe because sleep is a very complex phenomenon? Maybe we are looking in the wrong direction? Or maybe because we are studying sleep in highly artificial laboratory conditions? We need technological developments, but we also need new original ideas."
An important recent development in sleep research that has helped to advance the field is the emergence of novel transgenic and viral approaches that enable researchers to selectively label and manipulate specific neurons or specific brain areas. This breakthrough means researchers can now determine connectivity patterns between neurons and their contribution to specific characteristics and behaviours, such as sleep. However, a consequence of this is the emergence of a highly complex picture. Prof Vyazovskiy says: "In recent years, the list of newly discovered 'sleep-wake centres' in the brain and factors responsible for 'sleep need' have grown almost exponentially, and we are currently grappling with a lack of a solid theoretical framework that could address this growing complexity. In my opinion, it is becoming very important that we should study sleep in more ecological settings (where sleep evolved) rather than in laboratory conditions only, and across different species, which adapted their sleep patterns to unpredictable and often harsh environments." In light of this, "Physiology of Sleep" includes articles discussing both lab-based findings alongside sleep studies obtained in the wild and studies undertaken in various species and experimental models.
Furthering the conversation on the importance of studying sleep in our natural environment, the special issue also includes a paper from the Vyazovskiy Group first authored by Dr Laura McKillop, "Sleep and ageing: from human studies to rodent models." We learn a great deal about the basic neurobiology of ageing from animal models, but there are notable differences between species. It is known that when humans get older we usually sleep less and our sleep becomes more superficial. In contrast, as laboratory mice get old they sleep more and their sleep is found to be deeper. The origin of this discrepancy is unclear and has so far received little attention in the research world. In this paper, Dr McKillop and Prof Vyazovskiy discuss potential methodological differences between studies and draw attention to the role of the environment, which can play a different role in age-dependent sleep alterations in laboratory mice and humans. In doing so, they highlight the importance of studying the relationship between ageing and sleep in both humans and animal models, a message they delivered during a research spotlight given at the launch of the Physiological Society report "Growing Older, Better" at the Houses of Parliament last October.
The full issue "Physiology of Sleep" can be viewed on the Current Opinion in Physiology website, fronted by an Editorial overview from Vladyslav Vyazovskiy and A. Jennifer Morton.