Those who are easily distracted from the task in hand may have "too much brain".
So says Ryota Kanai and his colleagues at University College London, who found larger than average volumes of grey matter in certain brain regions in those whose attention is readily diverted.
To investigate distractibility, the team compared the brains of easy and difficult-to-distract individuals.
They assessed each person's distractibility by quizzing them about how often they fail to notice road signs, or go into a supermarket and become sidetracked to the point that they forget what they came in to buy. The most distractible individuals received the highest score.
The team then imaged the volunteers' brains using a structural MRI scanner. The most obvious difference between those who had the highest questionnaire scores – the most easily distracted – and those with low scores was the volume of grey matter in a region of the brain known as the left superior parietal lobe (SPL). Specifically, the easily distracted tended to have more grey matter here.
To find out whether activity in the left SPL plays a role in distractibility, the team turned to transcranial magnetic stimulation. This hand-held magnet dampens the activity of the part of the brain beneath it for around half an hour.
First, the researchers asked 15 volunteers to perform a timed task both with and without a distraction. The difference in the time taken to perform the tasks is a measure of how easily distracted a person is, says Kanai.
When the same individuals later repeated the exercise following transcranial magnetic stimulation over the left SPL to dampen its activity, the time each took to complete the task increased by around a quarter, on average.
"This suggests that the left SPL is involved in top-down control of attention," says Kanai.
Together, the two experiments suggest that the left SPL works to overcome distraction, and that those with larger left SPLs are more easily distracted.
Quite why SPL size works this way is unclear, but Kanai speculates that it may be linked to that fact that as we mature, the brain's grey matter is pruned of neurons in order to work more efficiently.
He suggests that a greater volume of grey matter may indicate a less mature brain, perhaps reflecting a mild developmental malfunction. "This theory would fit in with the observation that children are more easily distracted than adults," Kanai says.
But all is not lost for the distracted. Having identified that the left SPL plays a role in distraction, Kanai's team has begun to test ways to improve levels of attention by stimulating the left SPL using a technique called transcranial direct current stimulation. This involves placing electrodes on the head to deliver an unnoticeable electrical current to the immediate area.
"There are some signs that we can modulate attention" using transcranial direct current stimulation near to the left SPL, Kanai says. If confirmed, the technique might be useful for people whose distractibility becomes problematic, such as those with attention deficit hyperactivity disorder (ADHD).
Journal reference: Journal of Neuroscience, DOI: 10.1523/jneurosci.5864-10.2011
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