A new study, published in the journal Nature Neuroscience, has provided more insight into the head-direction cells located in our brains documented in previous studies. The researchers found that these cells are also active during deep sleep.
Head-direction cells arranged in a circle in order of their relative head directional preferences
Findings of past studies showed that the brains of mammals are equipped with an internal compass made of head-direction cells. The activity pattern of these cells changes when the head points at a specific direction. Now, it has been observed in mice that these cells are as electrically active during deep sleep as they are during wakefulness.
The team of researchers have spent two years filming the head movements of the mice while keeping track of the activity of the head-direction cells during sleep and when they navigated through their environments.
Gyorgy Buzsaki, senior investigator and Biggs Professor of Neural Sciences at NYU Langone, said in a statement:
“We have long known that the brain is at work during sleep. But now we know how it is working in one of the seemingly simpler senses – head orientation – or our sense of where we look at in any given space.”
Another important discovery was made during the experiment. When the mice would turn their heads while they were asleep, the head-direction neurones would display the same firing patterns as when they received vision and balance signals when awake.
The researchers explained that the “internal compass” would continue to work during sleep, as if it would code for the “direction of the gaze”.
Furthermore, they found that during rapid eye movement (REM) sleep, the firing activity of the cells in question moved at the same speed as they do during the awake state.
The findings might provide precious information to devise new treatments for brain and nerve disorders like Alzheimer’s disease whereby the navigation system deteriorates.
The authors suggest that these cells being active during sleep might mean that something is happening in the brain that corresponds to shifts in the gaze when it moves during wakefulness. It seems that the brain is still actively exploring and coordinating even when the animal is not nagivating through its environment.
Lead author Dr. Adrien Peyrache, a postdoctoral fellow in Buzsaki’s lab, says:
“The coordinated activity during the majority of sleep likely represents a consolidation of places, events and times, a sort of navigational backup system in the brain, during which the brain stores a map to memory.”