A latest study published in Cell Reports has found that during sleep human brains replay experiences that they learn while awake. This is the first time scientists have been able to glimpse at this process directly.
The memory replay while sleeping is attributed to a mechanism called memory consolidation that converts short-term memory to long-term memory to recall later.
Congrats to #BrainGate's Beata Jarosiewicz and Jean-Baptiste Eichenlaub on their paper showing replay of learned neural firing sequences during rest in human motor cortex!@MGHNeuroSci @MGH_CNTR @CarneyInstitute @VAResearch @brownengin @kibm_ucsd
— BrainGate Team (@BrainGateTeam) May 5, 2020
A study was conducted by Jean-Baptiste Eichenlaub of Massachusetts General Hospital and Beata Jarosiewicz, formerly research assistant professor at BrainGate, and now senior research scientist at NeuroPace. The research data confirms that spiking neuronal patterns constructing learned movement sequences are replayed during rest.
Brain-Computer Interface Paradigm
The study provided the direct evidence of learning related replay of memory traces after initial acquisition from sensory input to transform the new information into permanent information while sleeping. The study used a brain-computer interface to test the memory replay in human brain.
Dr. Richard Isaacson, neurologist who directs the Alzheimer’s Prevention Clinic at Weill Cornell Medicine and New York-Presbyterian Hospital, says:
Despite decades of research, it remains somewhat unclear how ‘short-term’ memories get filed away to become ‘long-term’ memories that can be recalled later. Using a brain-computer interface is an exciting way to study memory since it can record brain cell activity patterns and then look for those exact patterns later.
Two participants were studied as a model in a pilot clinical trial at BrainGate where they had two 96 channel intracortical silicon microelectrode arrays placed recurrently via neurosurgery as part of brain-computer interface. Participants were able to control the imagery-based brain-computer interface. They attended 1-3 sessions, each of 3-4 hours, per week. One participant had amyotrophic lateral sclerosis (ALS), a motor neuron disease that causes the death of neurons controlling voluntary muscles. The other participant had tetraplegia, a complete paralysis from below the jaw, due to cervical spinal cord injury.
In this study, the scientists used interface model to determine the memory replay in human brain of two participants by recording neuronal spiking activity from motor cortex, a part of brain that originates nerve impulses required for initiating voluntary muscular activity. Detected neural activity from microelectrodes was transmitted through a cable to the computer system and subjected to further processing and decoding.
Participants were asked to play Simon sequence game, a neural controlled sequence copying game. Participants took a nap before and after playing the game. The game consists of various repetitions of one ‘repeated’ sequence interspersed with varying ‘control’ sequences. The results showed that both participants performed repeated sequences more accurately than control sequences, consistent with learning.
The results showed that neuronal activity during those naps and during the time of playing the game was similar. This explains that regardless of their neurological disorders, during the time participants were asleep, their brain kept playing the Simon game because of replaying of same neuronal patterns at a neuron level inside the brain.
Dr Issacson says it is important to prefer soothing restful activities, particularly an adequate sleep, to enhance the memory function and learning. He says:
This supports the notion that in order to optimize memory function and learning, people need to prioritize restful activities — most importantly adequate sleep — to keep our ‘engines’ running at peak performance.
Understanding how memory is stored in the brain may help in understanding the cognitive behaviors and functions in memory consolidation. It can also help in understanding how exactly sleep stage is involved in developing long-term memory. Moreover, it is essential to have an adequate sleep. However, sleep duration requirements vary across age. It is also significantly impacted by lifestyle factors and health which affect its quality as well as duration.