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 form 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, hearth when new occasions occur, similar 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 observe movies exhibiting sequences of occasions.

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“It has lengthy been appreciated in psychology that reminiscence will not be steady, that it’s shaped in chunks. However this has by no means been noticed on the single neuron degree,” says Ueli Rutishauser at Cedars-Sinai Medical Heart in Los Angeles.

A lot about how reminiscences type continues to be unclear, however a number of insights have emerged from finding out 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 could keep in hospital for a number of days with electrodes implanted to report mind exercise. Every electrode has eight tiny wires protruding from it, and every wire can distinguish exercise from as much as 5 surrounding neurons.

Within the newest research, Rutishauser’s workforce requested 19 such folks to observe fastidiously constructed movie sequences whereas the recording passed off, listening to about 30 cells per particular person.

About 7 per cent of the neurons have been boundary cells, whose firing peaked when new issues occurred. “They don’t say something in regards to the reminiscence content material, they only say there’s 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 footage from the movies, they have been higher at remembering scenes from straight after a boundary than those who had occurred a number of seconds later.

The findings “make lots of sense”, says Rodrigo Quian Quiroga on the College of Leicester, UK. “They counsel a mechanism by which the hippocampus is signalling what scenes to place collectively and what scenes to not put collectively.”

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 exams involving phrases or nonetheless footage, not movies, says Rutishauser.

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

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