During sleep, a recent study found that the brain weakens the new connections between neurons that were formed while awake, but this only occurs during the first half of the night’s sleep. The study, conducted by UCL scientists on fish, was published in Nature. While the findings shed light on the role of sleep, they also raise questions about the function of the latter half of a night’s sleep.
The study supports the Synaptic Homeostasis Hypothesis, a theory on the purpose of sleep which suggests that sleeping acts as a reset for the brain.
Professor Jason Rihel, the lead author, stated that when we are awake, the connections between brain cells become stronger and more complex. If this activity were to continue without interruption, it would be unsustainable. Too many active connections between brain cells could prevent new connections from being made the following day.
Despite the mysterious function of sleep, it may serve as an ‘off-line’ period for the brain to rebalance itself.
brain of sleep, the fish showed an increase in synapse formation and maintenance during the next sleep period. This suggests that the need for sleep plays a role in the process of synaptic pruning, or the elimination of unnecessary connections in the brain, to prepare for new learning experiences.
The study used optically translucent zebrafish with specific genes that make synapses easy to observe. The researchers monitored the fish through multiple sleep-wake cycles and found that brain cells form more connections during waking hours and then lose them during sleep. The amount of sleep pressure the animal experienced before resting influenced this process, as sleep-deprived fish showed increased synapse formation and maintenance during the next sleep period. This indicates that the need for sleep is involved in the elimination of unnecessary brain connections in preparation for new learning.The study found that fish were able to catch up on lost sleep by experiencing increased connections between neurons, even after being deprived of sleep. Professor Rihel explained that this process of synapse reshaping may be less effective during mid-day naps when sleep pressure is low, compared to the nighttime when sleep is needed the most. The researchers also discovered that these changes in neuron connections mainly occurred during the first half of the fish’s nightly sleep, aligning with the pattern of slow-wave activity in the sleep cycle.The start of the evening.
According to Dr. Anya Suppermpool (UCL Cell & Developmental Biology and UCL Ear Institute), “Our research supports the idea that sleep helps to weaken connections in the brain, getting ready for more learning and forming new connections the next day. However, our study does not provide any information about what happens during the latter part of the night. There are other theories about sleep being a time for clearing waste from the brain, or repairing damaged cells – maybe other functions come into play during the second half of the night.”
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