For decades, scientists have been discovering neurons with seemingly unique jobs. There are place cells that fire in response to a particular location, mirror neurons that may help us interpret behaviours and even neurons that respond to all things Jennifer Aniston. These discoveries have encouraged a picture of the brain as a collection of highly specialised cells.

But a new discovery suggests that most neurons are actually jacks-of-all-trades. “These [earlier] neurons are really the exception, not the rule,” says Stefano Fusi at Columbia University in New York. And the more abundant, generalised cells “can be as important or more important than the good-looking [specialist] neurons we isolated in the past”, he says.

In a 2013 study, Fusi noticed “mixed selectivity” neurons – cells that respond to multiple different task-related inputs at the same time – in the brains of monkeys. But it was unclear how widespread they are in the mammalian brain. Advertisement Now, Fusi and his team have turned to the International Brain Laboratory.

This holds information on the activity of individual neurons throughout the brains of more than 100 mice while they did a decision-making task. The task involved the mice looking for an image on the left or right side of a screen and moving it to the centre by quickly turning a wheel. The researchers found that the only areas with specialised neurons were those in dedicated sensory cortices, such as the primary visual cortex.

Instead, the neurons in most areas of the brain responded to various aspects of the task. For instance, those outside of the visual cortex also seemed to be involved in processing the image, as well as deciding which side of the screen it was on and generating the movement to turn the wheel. “The important thing to stress is that there are specialised neurons [such as place cells],” says Fusi.

But these are not the norm, he adds. The researchers also found that most neurons didn’t respond in the same way to the same stimulus. For example, the somatomotor areas, which are regions associated with planning movements, responded strongly to licks and whisker movements.

Other areas still responded, but not as strongly. This suggests that while specialism exists, individual neurons generally aren’t myopically focused on one type of information. “The problem is if you’re arguing there’s no [specialisation], somebody can always say: ‘You just needed [to study] a few more neurons [to uncover it],’” says Ben Hayden at Baylor College of Medicine in Texas.

“This [study] is a giant smack in the face saying: ‘Fine, we got 14,000 neurons and we still didn’t find it [for the most part].’” Having a collection of neurons that respond to the same stimulus in slightly different ways may maximise the amount of information the brain can process. This may mean that these generalised neurons contribute to a plethora of tasks, including memory, cognition, decision-making and perception. The researchers point out that the mice’s task wasn’t particularly complex.

A complicated, multidimensional set of tasks could shed light on when individual neurons focus their responses on one aspect of such tasks versus another, says Fusi.