The reason why even professional basketball and soccer players sometimes miss an easy shot may be partly explained by spontaneous fluctuations of electrical activity within the brain, a study suggests.

An experiment conducted by researchers at Washington University, in Missouri, US, found that fluctuations in brain activity caused volunteers to subconsciously exert slightly less physical force when pressing a button on cue. Crucially, this activity is independent of any external stimulus and does not appear related to attention or anticipation.

The scientists involved say it is the first direct evidence that internal instabilities – so-called “spontaneous brain activity” – may play an important role in the variability of human behaviour.

From the mid-1990s onwards, brain-scanning techniques have revealed variable brain activity that appears unrelated to external stimuli and occurs even when a person is asleep or anaesthetized.


But just how such fluctuations in neuronal firings may influence physical behaviour has proven different to untangle. To explore the issue, Michael Fox at Washington University and colleagues designed an experiment that involved monitoring volunteers’ brains using functional magnetic resonance imaging (fMRI) as they performed a simple finger-tapping task.

Weaker response

The 17 volunteers were asked to push a button with their right hand as soon as they saw an on-screen prompt and the timing and force of each button press were recorded.

As expected, the brain scans revealed increased activity within the left motor cortex – the region associated with controlling movement of the right hand – shortly after each button-pushing prompt.

Fox and colleagues also monitored spontaneous activity within the left motor cortex by analysing its “mirror image” in the right motor cortex. This allowed them to see how spontaneous brain activity affected each button press, independent of the “task-related” brain signals.

The researchers found that volunteers pressed the button with about half the force, on average, if spontaneous activity occurred a few seconds before each prompt.

Missed goals

“This is the first clear evidence that [spontaneous brain activity] has some behavioural significance,” says Rasmus Birn of the National Institute of Health in Maryland, US, who was not involved with the research.

Fox admits that it remains unclear how spontaneous activity in the motor cortex might cause people to tap their fingers more gently, but speculates that it could be because the activity fools the brain into thinking the finger has already moved partly towards the button.

He suggests that spontaneous brain activity may perhaps explain why people engaging in sports sometimes miss an apparently easy goal or basket, by altering the force with which they kick or throw a ball.

However, Birn cautions that, “it remains to be seen whether this result holds for more complex cognitive tasks or other brain regions or networks”.

Journal reference: Neuron (DOI: 10.1016/j.neuron.2007.08.023)

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