Research into memory disorders, including autism and Alzheimers disease, has implications for understanding how the brain maps the space around us. Subjects often have a wrong perception of space-time and events. It was previously believed that only neurons from the visual cortex were capable of mapping the positions of moving objects. To contribute to spatial exploration or cognitive tasks, the hippocampus (the memory-making portion of the brain) was required.
A UCLA study found that hippocampal neuron in rats accurately maps the position of moving objects, even though the rat is stationary. These results are a challenge to the notion that the hippocampus (a brain region involved in learning and memory) only encodes a map space based on movement.
Panel a shows the rat sitting in the middle of an augmented reality setup. There is a green light bar moving around him. Panel b shows the top-down view of the maze. Panel c shows the activity of four neurons as a function o the bar position. The angular position of a bar of light is encoded by neurons even though the rat isn’t moving. This challenges the hypothesis that the hippocampus needs exploration to create an abstract map. Graphic courtesy Dr. Mayank Mehta.
These findings solve long-standing mysteries about hippocampal function. They also open up new avenues for early diagnosis and treatment of memory disorders. Mayank R. MehtaDr., UCLA Head of the W. M. Keck Center for Neurophysics and Professor in the UCLA departments of physics, neuroscience, electrical and computer engineering.
He said that it allows scientists to study cognitive deficiencies such as the subjects memory of events surrounding them, which is the most common type of Alzheimer’s disease.
The study was published in Published in Nature, was performed by scientists at UCLA’s W. M. Keck Center for Neurophysics. Lead authors were Chinmay Purandare, Ph.D., and Shonali Dahingra, Ph.D.
A VR experiment
Dr. Mehta explained that researchers used a modified virtual reality maze to test the hippocampuss memory function. A single bar of light was placed on the VR screen and moved around the rat like a person walking around you, while you are seated. Previous studies had shown that simple stimuli didn’t trigger the hippocampus. UCLA researchers suggested that this could be due to the large size of the stimuli.
The researchers measured neural signals to find that the majority of neurons of the rats’ hippocampus were responding to the bar of lights. They also logged the exact position and direction of the bar of light and the distance and angular degrees it was from the rat. The neurons also encoded information about the bar of light, such its color and texture.
These results disprove the notion that the hippocampus needs to move in space to create a spatial map. Dr. Mehta stated that the neural response is very similar to activity patterns within the visual cortices. This makes sense, since the visual cortex provides a lot of input to hippocampus.
The VR system will be used by the team to further investigate the neural activity of patients with memory impairments like Alzheimer’s disease.
Refer to: Purandare CS, Dhingra S, Rios R, et al. The immobile rat hippocampus is affected by the moving bar of light. Nature. 2022;602(7897):461-467. doi:10.1038/s41586-022-04404-x
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