The study focused on the loss of connectivity between neurons in the hippocampus, a region of the brain associated with learning and memory and how sleep deprivation negatively affects memory.
“It’s clear that sleep plays an important role in memory – we know that taking naps helps us retain important memories. But how sleep deprivation impairs hippocampal function and memory is less obvious,” said Robbert Havekes, assistant professor at the Groningen Institute for Evolutionary Life Sciences.
It has been proposed earlier that changes in the connectivity between synapses – structures that allow neurons to pass signals to each other – can affect memory.
To study this further, the researchers conducted the test on mouse brain and examined the impact of brief periods of sleep loss on the structure of dendrites, the branching extensions of nerve cells along which impulses are received from other synaptic cells.
They first used the Golgi’s silver-staining method to visualise the length of dendrites and number of dendritic spines in the mouse hippocampus following five hours of sleep deprivation, a period of sleep loss that is known to impair memory consolidation.
Their analyses indicated that sleep deprivation significantly reduces the length and spine density of the dendrites belonging to the neurons in the CA1 region of the hippocampus.
They repeated the sleep-loss experiment, but left the mice to sleep undisturbed for three hours afterwards. This period was chosen based on the scientists’ previous work showing that three hours is sufficient to restore deficits caused by lack of sleep. The effects of the five-hour sleep deprivation in the mice were reversed so that their dendritic structures were similar to those observed in the mice that had slept.
The researchers then investigated what was happening during sleep deprivation at the molecular level.
“Our further studies revealed that the molecular mechanisms underlying the negative effects of sleep loss do in fact target cofilin. Blocking this protein in hippocampal neurons of sleep-deprived mice not only prevented the loss of neuronal connectivity, but also made the memory processes resilient to sleep loss,” Havekes added, in the paper published in the journal eLife.