U.S. researchers discover new class of memory cells in the brain

TORONTO —
Researchers from Rockefeller University in the U.S. have discovered a new class of memory cells in the brain that specialize in recognizing a familiar face – similar to the hypothetical “grandmother neuron.”

A “grandmother neuron,” a single cell at the crossroads of sensory perception and memory which prioritizes an important face over others, has long remained elusive as scientists have searched for a class of brain cells that could explain the visceral reaction felt when someone sees a familiar face – like that of a grandmother, according to a release.

A new study, published in the journal Science on Thursday, reveals a new class of neurons in the brain’s temporal pole region that links face perception to long-term memory.

Instead of a singular “grandmother neuron,” they are a population of cells that collectively remember familiar faces.

“If you wanted to ridicule someone’s argument you would dismiss it as ‘just another grandmother neuron’ — a hypothetical that could not exist,” said professor of neurosciences and behaviour at Rockefeller University Winrich Freiwald in a release. “Now, in an obscure and understudied corner of the brain, we have found the closest thing to a grandmother neuron: cells capable of linking face perception to memory.”

Freiwald and his colleagues found that a small area in the brain’s temporal pole region may be involved in facial recognition, and by using magnetic resonance imaging as a guide, “zoomed in” on two temporal regions of two rhesus monkeys.

They then recorded the electrical signals emitted as they showed the monkeys images of familiar faces they had seen “in person,” and unfamiliar faces they had seen only on a screen.

The researchers found that the neurons in the temporal pole region were “highly selective” according to the study, responding to faces that the test subjects had seen before more strongly than unfamiliar ones, and the neurons were fast – “discriminating between known and unknown faces immediately upon processing the image.”

The findings showed that the temporal pole neurons responded three times as strongly to familiar versus unfamiliar faces, even though the monkeys had seen the unfamiliar faces many times, albeit on a screen.

“This may point to the importance of knowing someone in person,” said study author Sofia Landi in the release. “Given the tendency nowadays to go virtual, it is important to note that faces that we have seen on a screen may not evoke the same neural activity as faces that we meet in person.”

The findings are the first evidence of a “hybrid brain cell” the study posits, describing the cells of the temporal pole region acting like sensory cells, with reliable and fast responses to visual stimuli and a reaction similar to memory cells that respond only to stimuli the brain has seen before.

“We have discovered a connection between the sensory and memory domains,” Freiwald said, adding that instead of a singular “grandmother neuron,” the team found the cells of the temporal pole region work as a collective.

Researchers hope to continue their work, noting that their discovery means that future studies can investigate how those neurons encode familiar faces – and their findings may have clinical implications for people who suffer from prosopasnosia, or face blindness, a condition that affects about one per cent of the population.

“Face blind people often suffer from depression, it can be debilitating,” Freiwald said, noting that in the worst cases, people who suffer from face blindness cannot even recognize close relatives.

“This discovery could one day help us devise strategies to help.”