Undoubtedly, our ability to create and retrieve memories is a fundamental part of the human experience, but we still have a lot to learn about this process. For example, scientists today lack a clear understanding of how different areas of the brain interact to form and retrieve memories. However, the results of the latest study shed light on this phenomenon, showing how neural activity occurs in two separate areas of the brain during recall of memories - the hippocampus and the neocortex. The work was published in the journal PNAS (Proceedings of the National Academy of Sciences).
How the hippocampus and neocortex help retrieve memories
The hippocampus, a structure located deep in the brain, has long been considered the center of memory. The hippocampus helps to "glue" fragments of memories ("where" and "when"), allowing neurons to work together. This is often referred to as "neural synchronization". When the neurons that encode the "where" information synchronize with the neurons that encode the "when" information, those details become connected through a phenomenon known as "Hebbian theory." But the hippocampus is simply too small to store every single piece of memory. This led the researchers to the theory that the hippocampus harnesses the neocortex - the region of the brain that processes complex sensory details such as sound and vision - to help fill in the details of memories.
However, the work of the neocortex is the exact opposite of the work of the hippocampus - the neocortex ensures that neurons do not work together. Researchers call this "neural desynchronization." Imagine asking 100 people to say their names at the same time. Obviously, the synchronicity of their response will make the recognition of each individual name impossible. But if each person desynchronizes their response (that is, people take turns pronouncing their names), you are likely to gather much more information from them. The same applies to neurocortical neurons - if they are synchronized, then they struggle to convey the message, but if they desynchronize, the information is easily transmitted.
Understanding how the brain forms and retrieves memories can help fight diseases such as dementia and Alzheimer's.
The researchers' work has shown that the hippocampus and neocortex do work together when it comes to memories and retrieval. The hippocampus synchronizes its activity with the neocortex to glue pieces of memories together, and the neocortex later helps to extract them. Meanwhile, the neocortex desynchronizes its activity to help process information about the event and retrieve memories later.
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During the study, scientists tested 12 patients with epilepsy, aged 24 to 53 years. All subjects had electrodes placed directly in the brain tissue - the hippocampus and neocortex - as part of the treatment for epilepsy. During the experiment, patients studied associations between various stimuli (such as words, sounds and videos) and then remembered them. So, scientists found that during training, neural activity in the neocortex is desynchronized, and then, after about 150 milliseconds, neural activity in the hippocampus is synchronized. Apparently, information about the sensory details of stimuli is first processed by the neocortex and then transferred to the hippocampus for adhesion. The researchers found that the hippocampus and neocortex interact closely in the formation and recovery of memories.
These results support a recent theory that suggests that the desynchronized neocortex and the synchronized hippocampus must interact in order for a person to form and then retrieve memories. Understanding how the hippocampus and neocortex work together to form and retrieve memories may be important for the further development of new technologies that can help improve the memory of people suffering from cognitive impairments such as dementia, as well as improve memory performance in general. …
Lyubov Sokovikova
