At Quanta, staff writer Yasemin Saplakoglu reports on concept cells, which are believed to be unique to humans:

Concept neurons fire for their concept no matter how it is presented: in real life or a photo, in text or speech, on television or in a podcast. “It’s more abstract, really different from what you’re seeing,” said Elizabeth Buffalo, a neuroscientist at the University of Washington.

“Concept Cells Help Your Brain Abstract Information and Build Memories,” January 21, 2025

In the past, the idea that such cells could exist was ridiculed:

For decades, neuroscientists mocked the idea that the brain could have such intense selectivity, down to the level of an individual neuron: How could there be one or more neurons for each of the seemingly countless concepts we engage with over a lifetime? “It’s inefficient. It’s not economic,” people broadly agreed, according to the neurobiologist Florian Mormann at the University of Bonn.

But when researchers identified concept cells in the early 2000s, the laughter started to fade. Over the past 20 years, they have established that concept cells not only exist but are critical to the way the brain abstracts and stores information. New studies, including one recently published in Nature Communications, have suggested that they may be central to how we form and retrieve memory. “Build Memories”

3D illustration of Interconnected neurons with electrical pulses. Photo by ktsdesign on Adobe Stock

The existence of the cells was verified by studying epilepsy patients facing surgery in areas of the brain that are associated with memory. They had electrodes implanted in their brains for medical purposes already, so that neurology and neurosurgery staff could identify and map functional areas, to ensure that they did not damage them.

One of the researchers, Rodrigo Quian Quiroga, found that these cells respond individually to a variety of concepts organized around a single person, place, or thing. For example,

Quiroga wrote out the name “Oprah Winfrey.” The same neurons that had fired for her picture also fired for her name. That meant that the neurons weren’t responding to features of the picture, such as brightness or color: They were context-independent. They were responding to Oprah as a concept. “Build Memories”

Hence the name concept cells. From the 2005 paper that resulted from the research:

We have previously shown that neurons in the human medial temporal lobe (MTL) fire selectively to images of faces, animals, objects or scenes. Here we report on a remarkable subset of MTL neurons that are selectively activated by strikingly different pictures of given individuals, landmarks or objects and in some cases even by letter strings with their names. These results suggest an invariant, sparse and explicit code, which might be important in the transformation of complex visual percepts into long-term and more abstract memories.

Quiroga, R., Reddy, L., Kreiman, G. et al. Invariant visual representation by single neurons in the human brain. Nature 435, 1102–1107 (2005). https://doi.org/10.1038/nature03687

Concept cells might get reprogrammed as well:

It’s possible that these neurons can play different roles and take on different identities based on the task at hand, Buffalo said. When it needs to be a concept cell for Jennifer Aniston, that’s what it is. When it needs to be a place cell to help you navigate toward the martini at the bar, it is a place cell. “That cell is like a Swiss Army knife,” [neuroscientist Cory] Miller suggested. “Build Memories”

The key to abstraction?

Image Credit: underworld - Adobe Stock

The whole area is very new. There is often a tendency in such cases to draft something so new (and unique) into an existing framework of beliefs, developed from other evidence. At Salon, for example, science writer Carlyn Zwarenstein focuses on the idea that concept cells may be what makes humans more intelligent than, say, chimpanzees:

For humans, unlike our fellow animals, we just want the key point, the essential abstraction. That, Quian Quiroga maintains, is the way we remember, and the way we think. And that’s what he shows with the new study, published in Cell Reports. The research team recorded the activity of individual neurons while patients learned and then recalled two stories that described different situations but featured the same character or place. Nearly all of the neurons that fired initially did so without regard to the context, such that, as the authors explain, “taking all neurons together it is possible to decode the person/place being depicted in each story, but not the particular story.”

The brain cells that fire during learning and memory are firing in response to the concept of that character and will fire in any context in which that concept features. Quian Quiroga believes that the development of language involved adaptation of neurons, common to all mammals, to this specialized purpose. Still, we don’t know exactly when this arose, but perhaps it evolved gradually, Quian Quiroga theorized.

“I think in the last 100,000 years, the moment that [Homo] sapiens started uttering words and attributing meaning to things in terms of words,” Quian Quiroga said. “Then the sapiens started thinking in terms of words instead of pictures. I think that created the big phase transition of intelligence, the fact that we started thinking in terms of words. I think this created concept cells, because once you attribute the word into something then you get completely rid of the details. And that’s exactly what concept cells do.”

“What makes humans intelligent? These unique neurons might hold the key,” March 25, 2025

But it is also true that, at last count, there are more than 3300 types of cell in the human brain. And we don’t know what most of them do. It’s a lot to ask of one type of cell, however unique, that it be the type of cell that makes humans more intelligent than chimpanzees and created language.

More likely, Quiroga is pulling on one strand of a staggeringly complex web.