Published in journal Science is a new study that shows that sleep deprivation can interfere with the process that helps reinforce our memories.
Researchers at Johns Hopkins University in the US carried out a study on mice to strengthen evidence that one of the key purposes of sleep is to recalibrate the brain cells responsible for learning and memory thereby enabling animals to ‘solidify’ lessons learned and use them when they awaken. Further, the team of researchers also reveal several important molecules they discovered during the course of the study that are said to govern the recalibration process, and also published evidence that sleep deprivation, sleep disorders and sleeping pills can interfere with the process.
Current scientific understanding of learning suggests that information is “contained” in synapses, the connections among neurons through which they communicate. On the “sending side” of a synapse, signalling molecules called neurotransmitters are released by a brain cell as it “fires”; on the “receiving side,” those molecules are captured by receptor proteins, which pass the “message” along. If a cell receives enough input through its synapses, it fires off its own neurotransmitters.
Studies have shown that synapses on the receiving neuron can be toggled by adding or removing receptor proteins, thereby strengthening or weakening them and allowing the receiving neuron to receive more or less input from nearby signalling neurons. When neurons are “maxed out” and constantly firing, they lose their capacity to convey information, stymieing learning and memory. One possible reason that neurons do not usually max out is a process that has been well-studied in lab-grown neurons but not in living animals, asleep or awake.Known as homeostatic scaling down, it is a process that uniformly weakens synapses in a neural network by a small percentage, leaving their relative strengths intact and allowing learning and memory formation to continue.
To find out if the process does occur in sleeping mammals, researchers focused on the areas of the mouse brain responsible for learning and memory: the hippocampus and the cortex. They purified proteins from receiving synapses in sleeping and awake mice, looking for the same changes seen in lab-grown cells during scaling down. Results showed a 20 per cent drop in receptor protein levels in sleeping mice, indicating an overall weakening of their synapses, compared to mice that were awake.