The entire stadium goes silent, watching a basketball player line up for a free throw. He’s made this kind of shot thousands of times before, so he bends and releases the same way he always does and… he misses. Why is it that we can perform a task over and over, yet the results still vary after all that practice? The answer, it seems, lies in the response of a single neuron.

Neuroscientists at Duke University discovered that individual neurons vary in their activity when they’re presented with the same exact situation multiple times. This produces a type of noise in the brain that affects how it responds. The noise, according to researchers, may be behind common deviations like inconsistently signing your name and occasionally hitting the wrong key while typing.

“Understanding the noise in the nervous system and how it can work to cause inaccuracies in movement is a critical step in understanding how we move,” said study senior investigator Stephen Lisberger, chair of neurology at Duke University School of Medicine, in a statement.

The idea that our brains and the neurons they house are noisy is not new. Single neurons fire irregularly even when a person is performing a familiar motion, and the exact moment the cells spike with electricity is crucial for transmitting information. In the new study, however, Lisberger and his team found that a delay of one neuron firing in response to a particular motion led to a delay in another neuron in the visual region of the brain.

“I was extremely surprised by this finding,” Lisberger said. “My intuition would have been that it would have been entirely random.”

Lisberger likened a group of neurons to a rowdy crowd at a sporting event. He said that when they’re uncoordinated, individual cheers can be difficult to discern. When everyone chants in unison, however, the words are more easily picked out from other noise. The researchers call this synchronicity in neurons correlated noise and say it’s a meaningful signal.

The findings came from an experiment in which Lisberger’s team analyzed the electrical activity of single neurons firing in the brains of monkeys. The monkeys tracked a moving dot across a computer screen, an action guided by an area called MT within the visual region of the brain. The team saw that a delay in a single MT neuron would predict the size of the delay in the monkeys’ responding eye movements.

‘We get that finding because the whole population of neurons is correlated and they are fluctuating together,” Lisberger said. “That’s the key internal driver.”

He added that the team’s future work will hopefully zero in on variations of individual neurons in motor areas of the brain.

Source: Lee J, Joshua M, Medina J, Lisberger S. Signal, Noise, And Variation In Neural And Sensory-Motor Laterncy. Neuron. 2016.