A person’s memory is where the brain encodes, stores, and retrieves information, where it can also be used as a record of experience for guiding learned behavior. Different areas of the brain encode or stores different types of memory, for instance, the hippocampus is related to spatial memory, which helps the brain map the surrounding world and finds its way around a known place. The amygdala, on the other hand, is linked to emotional memory, and the medial temporal lobe is responsible for both spatial navigation and memory. Although single neurons in the medial temporal lobe activate to represent locations in the environment during navigation, how this spatial tuning relates to memory for events involving those locations remains unclear. Now, a study from researchers at Columbia University identifies specific neurons in the human entorhinal cortex which are responsible for encoding place-based memories. The team states because the activity of these neurons is closely related to what a person is trying to remember, it is possible their activity is disrupted by diseases like Alzheimer’s, leading to memory deficits. The study is published in the journal Nature Neuroscience.
Previous studies show the hippocampus and entorhinal cortex are important for spatial cognition, demonstrated by the discovery of place cells and grid cells in these regions, neurons that activate to represent specific locations in the environment during navigation. However, it is unclear how this spatial map in the brain relates to a person’s memory of events at those locations, and how neuronal activity in these regions enables them to target a particular memory for retrieval among related experiences. The current study shows individual neurons in the human brain target specific memories during recall.
The current study maps memory-related changes in spatial tuning by recording single-neuron activity from neurosurgical patients performing a virtual-reality object–location memory task. The team measured the activity of neurons as the patients moved through the environment and marked their memory targets. Results identify memory-trace cells whose activity was spatially tuned to the location where subjects remembered encountering specific objects. Data findings show these memory-trace cells in the entorhinal cortex encoded discriminable representations of different memories through a memory-specific rate code.
The group states this memory-specific rate code allowed them to actually decode the specific memory a patient was targeting based on the activity of these neurons. They go on to explain initially they identified purely spatially tuned neurons that were activated when patients moved through specific locations, regardless of the subjects’ memory target. However, the memory-trace neurons only activated in locations relevant to the memory the patient was recalling for a particular trial, and whenever patients were instructed to target a different memory for recall, the memory-trace neurons changed their activity to match the new target’s remembered location.
The team surmises they have mapped single neurons in the human entorhinal cortex that alter their spatial tuning to target relevant memories for retrieval. For the future, the researchers state they plan to look for evidence these neurons represent memories in non-spatial contexts to better characterize their role in memory function.
Source: Columbia Engineering
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