People with brain lesions are helping researchers to zero in on the region that keeps us from responding to every stimulus we see.

Our actions reveal only part of the complex decision-making processes that go in our brains. Just as important is how we stop ourselves from reacting to things around us. Previous work had shown that visual stimuli automatically activate motor plans in the brain, but this activation is normally quickly suppressed so that we're not forever acting on what we happen to see. All this happens automatically, 'behind the scenes' - without our conscious knowledge.

By studying people with very specific brain lesions, Professor Masud Husain (University College London) and colleagues have now identified one key area of the brain that helps to block such reflexive actions. The researchers found that damage to small parts of the frontal lobe of the brain meant that such automatic suppression no longer occurred. Affected individuals no longer properly suppressed such reflexes.

Professor Husain, a Wellcome Trust Senior Research Fellow, proposes that this area of the brain helps to keep our actions from being constantly hijacked by reflexive responses. The team's findings may also help to explain the curious 'alien limb' syndrome, in which a person's hand may involuntarily grasp nearby objects, even people, and have great difficulty letting go. Such reflexive responses may normally be suppressed by parts of our frontal lobe.

• This research was funded in part by the Wellcome Trust.

Image credit: Heidi Cartwright, Wellcome Images

External links

• Sumner P et al. Human medial frontal cortex mediates unconscious inhibition of voluntary action. Neuron 2007;54(5):697-711.