How slow brain waves during deep sleep improve long-term memory

Scientists have been studying complex processes occurring in the human brain during deep sleep for many years, and one of the key discoveries of recent decades relates to the so-called slow brain waves. These electrical waves, also known as slow oscillations, play a crucial role in consolidating long-term memories. However, how exactly they affect the neocortex, the part of the brain responsible for storing information, was not clear until recently. A research team from Charité – Universitätsmedizin Berlin discovered the mechanisms that explain why these waves are crucial for the formation of lasting memories.

Sleep as the key to memory storage

During sleep, the human brain goes through different stages, with deep sleep, known as the slow-wave phase, standing out as especially important for memory processes. According to neuroscientists, the brain in this phase replays events and information from the previous day. It transfers this information from the hippocampus, where short-term memories are temporarily stored, to the neocortex, the part of the brain responsible for long-term memory. Slow oscillations, rhythmic changes in electrical voltage in the brain cortex, are crucial for this process. Their synchronization enables the transfer and permanent storage of information.

Synchronization of brain waves

Slow brain oscillations can be measured using an electroencephalogram (EEG), and their frequency is about one cycle per second. These low-frequency oscillations enable the simultaneous activation of a large number of neurons in the neocortex. According to Prof. Dr. Jörg Geiger, the head of the research, these oscillations not only stimulate memory processes but also increase the receptivity of synapses – the connections between nerve cells.

Revolutionary research on human tissue

The research team conducted an analysis on brain tissue samples collected from patients undergoing neurosurgical procedures for epilepsy or brain tumors. The samples were stored under special conditions to preserve their functionality. By simulating the slow oscillations characteristic of deep sleep, the researchers monitored neuronal reactions using advanced techniques such as the multipatch technique. This method allowed precise measurement of the activity of multiple synapses simultaneously, providing detailed insight into the communication between nerve cells.

Synaptic plasticity and timing

One of the key findings of the study was the discovery that synapses between neurons reach their highest efficiency at a specific moment within the cycle of slow oscillations. When the electrical voltage suddenly rises, the neocortex enters a state of heightened readiness to receive and store information. This brief time window, according to Dr. Franz Xaver Mittermaier, allows for the efficient transfer of memories from the hippocampus to long-term storage.

Practical applications of the discovery

The new findings open the door to the development of technologies that could enhance memory functions in humans. For example, transcranial electrical stimulation and acoustic stimulation are already being used to stimulate slow waves during sleep, but their application is currently based on trial and error methods. With a precise understanding of the timing mechanisms, it is possible to develop targeted stimulation methods that could help people with mild cognitive impairments or older individuals in preserving their memory.

The science behind slow waves

Slow waves are part of the spectrum of brain activities known as delta waves, and besides sleep, they can also occur in certain neurological disorders. Their role in processes such as synaptic plasticity and memory consolidation is the subject of intensive research, with potential for clinical applications. Thanks to such research, we are getting closer to understanding the complex processes that shape our ability to remember and learn.