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Our need for sleep may actually be regulated by brain cortex

Sleep is an essential part of your daily routine. Despite having several health benefits, sleep is also necessary for numerous brain functions. Everyone needs sleep, but the biological purpose of sleep remains obscure.

Why we sleep, what is the process behind sleep, etc., are some interesting questions. Finding the answer to these questions becomes essential to understand the science of sleep.

Scientistś from the University of Oxford, in a new study, have uncovered a new target for sleep studies within the cerebral cortex. The cerebral cortex makes up about two-thirds of the brain’s total mass. It is responsible for determining intelligence and personality, motor function, thoughts, language, attention, and memory.

Many previous sleep studies have used activities in the cerebral cortex to record sleep/wake patterns. This new study found that record sleep/wake patterns.

Scientists studied brain activities in laboratory mice. Neurons in two areas of the cortex – neocortical layer 5 and a part of the hippocampus – were ‘silenced’ in the mice’s brains.

Deactivation of neurons in these brain regions woke up lab mice for at least three hours longer every day. If mice have two hours lifespan, it means they gained three full months of ‘awake’ time over their lifespans. In human terms, this would equate to about ten years.

Though the mice were awake longer, their need for deep sleep did not appear to be affected. Usually, when mice (and humans) stay awake longer than usual and get more tired, we sleep more deeply to compensate. This study in lab mice found that they did not sleep any more deeply than usual. Their body clock i.e., circadian rhythm did not appear to be affected by the extra waking hours in their days.

Dr. Lukas Krone of the Department of Physiology, Anatomy, and Genetics, University of Oxford, and lead author on the study said, “Our finding that the cortex is part of the sleep-regulating system opens new perspectives for sleep medicine. It might be possible to use already-established non-invasive brain stimulation techniques to alter cortical activity and thereby moderate sleep for therapeutic purposes, such as for the treatment of sleep disorders.”

Professor Vladyslav Vyazovskiy, Head of Sleep, Brain and Behaviour Laboratory in the Department of Physiology, Anatomy, and Genetics and a member of Sleep and Circadian Neuroscience Institute (SCNi), a co-corresponding author on the paper, said, “The cortex is a highly complex structure, both anatomically and functionally, and is therefore difficult to study; and this is why we think its role in sleep control was previously overlooked. The effects on sleep of cortical silencing offer a novel and fresh perspective on the mechanisms of sleep control, and has the strong potential to transform the field of sleep neurobiology.”

Professor Zoltán Molnár, Head of Cerebral Cortical Development and Evolution Laboratory in the Department of Physiology, Anatomy, and Genetics and co-corresponding author on the paper, said, “Much effort and funding over the last decades has been spent on clarifying the role of subcortical structures in sleep regulation and the cerebral cortex was not the focus of attention. When we first performed our ‘silencing’ study on different cortical projection neurons, I expected phenotype from another neuronal population and not from layer 5 and hippocampus. For me, the discovery of its effect on the mice’s sleep was a great surprise.”

Dr. Krone said, “While this study is an important first step, more work needs to be done. We hope that many other research groups will investigate how exactly the cortex contributes to sleep regulations. A multidisciplinary approach will help us to understand the cellular mechanisms and neuronal circuits fully through which the cortex regulates sleep.”

Journal Reference:
  1. Krone, L.B., Yamagata, T., Blanco-Duque, C. et al. A role for the cortex in sleep-wake regulation. Nat Neurosci (2021). DOI: 10.1038/s41593-021-00894-6

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