The brain’s outer layer, called the cerebral cortex, contains many neurons. These neurons communicate through synapses, which are like bridges that pass information. The strength of these synapses can change based on how active the neurons are. This process is thought to be the foundation of learning and memory. Scientists have identified rules, called synaptic learning rules, that explain how the timing and frequency of neuron activity affect synapse strength. For example, the Hebbian rule and spike-timing-dependent plasticity (STDP) are two such rules. While it’s clear that sleep is important for learning and memory, how synapses change during sleep has been a mystery.
Key findings on sleep and synaptic strength
Researchers at The University of Tokyo studied how synapse strength in the cerebral cortex changes during sleep. They used computer simulations to mimic the activity of networks made up of different types of connected neurons. These simulations showed how synapses behave during sleep and wakefulness. The findings revealed that synapses can get stronger during sleep when certain levels of neuron activity follow typical synaptic learning rules. This process, called sleep learning, involves the brain organizing and strengthening new information during sleep to improve memory and learning. The study showed it’s possible to predict when sleep learning happens based on these conditions. The researchers also found that when neuron activity is much higher during wakefulness than sleep, synapses strengthen more during wakefulness. But when the activity levels are similar, sleep can enhance synapses more.
These discoveries help explain how sleep supports learning and memory. They may also shed light on brain disorders linked to sleep problems, such as mental health conditions. The research was part of the Ueda Biological Timing Project, funded by the Japan Science and Technology Agency. It was published in the journal PLOS Biology. By understanding how sleep affects synapses, scientists hope to learn more about how the brain processes information and how sleep disruptions impact health.