Brain cells: Special neurons may signal when to start new memories

Recordings from electrodes in folks’s brains reveal that sure neurons within the hippocampus present a burst of exercise to mark the boundary between totally different occasions


7 March 2022
, up to date 7 March 2022

Hippocampus neuron, computer illustration. The hippocampus in humans is the structure in the brain responsible for long-term memory.

Illustration of neurons within the hippocampus


A newly found sort of mind cell concerned in reminiscence formation appears to mark the boundary between distinct occasions as we expertise them.

The neurons, which have been known as boundary cells, fireplace when new occasions occur, akin to if we see somebody strolling right into a room.

The cells have been found in folks with epilepsy who had electrodes put into their mind earlier than surgical procedure, by asking them to look at movies exhibiting sequences of occasions.

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“It has long been appreciated in psychology that memory is not continuous, that it’s formed in chunks. But this has never been observed at the single neuron level,” says Ueli Rutishauser at Cedars-Sinai Medical Center in Los Angeles.

Much about how reminiscences type continues to be unclear, however a number of insights have emerged from learning individuals who want electrodes put into their hippocampi – two curved constructions on both facet of the mind – as a result of they’ve epileptic seizures that begin in these areas. The hippocampi and surrounding areas of the mind are essential for making new reminiscences.

To work out precisely which a part of the mind is malfunctioning, folks with epilepsy might keep in hospital for a number of days with electrodes implanted to document mind exercise. Each electrode has eight tiny wires protruding from it, and every wire can distinguish exercise from as much as 5 surrounding neurons.

In the most recent research, Rutishauser’s group requested 19 such folks to look at fastidiously constructed movie sequences whereas the recording occurred, listening to about 30 cells per individual.

About 7 per cent of the neurons have been boundary cells, whose firing peaked when new issues occurred. “They don’t say anything about the memory content, they just say there is a boundary,” says Rutishauser. He speculates that exercise in these cells alerts that the mind ought to start to type a brand new reminiscence, like beginning a brand new folder.

When folks have been examined later by exhibiting them photos from the movies, they have been higher at remembering scenes from straight after a boundary than people who had occurred a couple of seconds later.

The findings “make a lot of sense”, says Rodrigo Quian Quiroga on the University of Leicester, UK. “They suggest a mechanism by which the hippocampus is signalling what scenes to put together and what scenes not to put together.”

Boundary cells haven’t been seen earlier than as a result of earlier work in folks with electrodes implanted earlier than epilepsy surgical procedure used reminiscence assessments involving phrases or nonetheless photos, not movies, says Rutishauser.

Journal reference: Nature Neuroscience, DOI: 10.1038/s41593-022-01020-w

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