Researchers at the University of Michigan (UM) have discovered how sleep deprivation affects memory-making in the brain. They found out which function of the hippocampus was being hindered from doing its job.
In its official website, the University of Michigan reported that meddling with sleep-associated oscillations, also known as the rhythmic firing of neurons, in one subsection of the hippocampus could be the reason for the connection. The results of the study have been published in the journal "Nature Communications."
The researchers were led by UM graduate student Nicolette Ognjanovski. They recorded the baseline hippocampal activity of a group of mice as they placed the test subjects into a new environment, let them explore, gave them mild foot shock and put them back into their cages to let them sleep normally.
Sara Aton, an assistant professor in the Department of Molecular, Cellular and Developmental Biology who is the senior author of the paper, said that the mouse exhibited a stereotyped fear response when they were brought back to the same structure. However, depriving them of sleep after the context-shock pairing made them forget about it the next day.
In normally sleeping mice, it was found that sleep-associated oscillations in a part of the hippocampus called CA1 were more robust after learning. A new group of mice, on the other hand, were given a drug to inhibit a small population of inhibitory neurons in CA1 that express parvalbumin.
The researchers discovered that suppressing the parvalbumin-expressing cells led to the complete wipe out of the normal learning-associated increase in oscillations in that part of the mouse's hippocampus. It was noted that the mice forgot any fearful association with their task when their neurons were kept from firing together regularly and rhythmically.
This demonstrated how memories are not stored in single cells but are instead distributed through the network. The rhythmic firings that parvalbumin cells control are linked to global network changes, or stability.
