When "Too Much Brain" Is Bad For You

Easily distracted people may have too much brain

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.

The “certain brain region” [singular] is the left superior parietal lobe (SPL). And why is a larger left SPL associated with greater distractibility?? How do you explain this bizarre finding?

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.

Or, as it’s explained in the J Neurosci paper:

…A number of possible explanations can be offered from a developmental perspective.

During adolescence the synapses in human cortex undergo a pruning process (Huttenlocher and Dabholkar, 1997), which is supposedly linked with improved processing efficacy of pruned cortical regions. As the reduction of gray matter density due to the pruning process occurs between childhood and early adult life across broad areas of the cortex, including the left SPL, more mature brains tend to have smaller SPL (Gogtay et al., 2004). Considering cortical pruning as a process of maturation, it is conceivable that smaller volume (or gray matter density) of the left SPL leads to more efficient attentional control by this region.


From the group who brought you Political orientations are correlated with brain structure in young adults [but Colin Firth is not an author on this one].


Kanai R, Dong MY, Bahrami B, Rees G. Distractibility in daily life is reflected in the structure and function of human parietal cortex. J Neurosci. 2011 May 4;31(18):6620-6.