Groundbreaking research identifies what makes human brains – and humans – unique in the animal world

A neuroscientist at the University of Leicester has identified a fundamental difference between human and animal brains. This breakthrough, published today in the journal Cell, offers an explanation for what makes Homo sapiens so vastly different from even our nearest relatives. It could be the key to understanding human intelligence.

Professor Rodrigo Quian Quiroga, from our Department of Neuroscience, Psychology and Behaviour formerly discovered the so-called ‘Jennifer Aniston neurons’ or ‘concept cells’ – brain cells which fire repeatedly when the subject is shown different images of a particular person, or even that person’s name. The new article in Cell indicates that this type of neuron may be unique to humans. The research suggests that human memory differs from that of animals and hence is a potential root for high-level thoughts, based on concepts and abstractions, which are not found in even the most intelligent animals.

A great deal of neurological research has been done over the years on the brains of mice, rats and monkeys, which can be probed with electrodes to understand mechanisms of brain function. However, such research on humans is not allowed for obvious ethical reasons.

One of the very few situations in which an adult human has electrodes inserted into their brain is when they are being considered for surgery to treat epilepsy. This gives researchers such as Professor Quian Quiroga a unique opportunity to study the firing of individual human neurons in response to specific stimuli such as pictures and words.

Until now, it was believed that mammalian brains are all essentially similar across different species. Yet there must be some reason why humans evolved the way they did, differentiating themselves from other species. Other mammals can form memories, learn and think, but nowhere near the extent of humans. Even a young child rapidly outstrips other great apes in learning ability. Wherein lies the difference?

Professor Quian Quiroga proposes that ‘concept cells’ within the hippocampus, a part of the brain associated with memory, might be the answer. These cells have not been found in the hippocampus of monkeys or rats, suggesting that their presence can explain what makes humans different, leading to language, art, science and all the other manifestations of civilisation.

The key lies in the fact that a ‘concept cell’ fires to a specific subject, such as an actor or celebrity, irrespective of context. Whether the photograph of Jennifer Aniston shows her in character on a film set or walking the red carpet or relaxing at home, more or less the same neurons fire each time. They also fire when the subject sees or hears the actor’s name or makes an association, such as remembering seeing her in a particular place. Changing the clothes or context does not change the underlying ‘concept’ and so does not affect the neurons’ responses.

In contrast, studies in rats have shown that changes in their environment, such as a rearrangement of the arena where experiments take place, trigger a completely different set of neurons. The rat’s neurons do not respond to a slightly changed environment as the same place; changes in context change the neurons’ firing. Professor Quian Quiroga argues that concept cells in human brains, which store an abstract representation – the meaning of the stimulus, devoid of details and contextual information – might be key for making inferences, analogies and high-level associations that humans do naturally and effortlessly

This is the first time that a fundamental biological aspect has been identified which distinguishes human brains from those of other species.

Professor Quian Quiroga said: “The proposal that concept cells may be the key of human memory and our unique cognitive abilities is quite bold and at the same time fascinating. One just needs to realise that a chimpanzee’s brain is about a third of the size of a human brain to understand that there should be something radically different in the way the human brain functions. The idea that concept cells are key to human intelligence has wide reaching connotations to understand cognitive differences with other species and perhaps with artificial intelligence. Right or wrong, it will hopefully open new discussions about what makes us human that go beyond plain philosophy and are based on neuroscientific findings.”

Professor Ian Forsythe, Head of the Department of Neuroscience, Psychology and Behaviour at the University of Leicester, said: “Rodrigo Quian Quiroga’s research and ideas are challenging what we thought we knew about human cognition, and have far reaching consequences for understanding the brain and of what makes us human.”

• ‘Plugging in to Human Memory: Advantages, Challenges, and Insights from Human Single-Neuron Recordings’ doi: 10.1016/j.cell.2019.10.016