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Consciousness and Intention
Where in the brain are our intentions formed and how do we become aware of these intentions? Desmurget et al. (p. 811; see the Perspective by Haggard) investigated the effect of direct cortical stimulation of parietal and premotor regions in patients undergoing brain surgery for tumor removal. Stimulation of the parietal lobe provoked the conscious experience of wanting to move the upper limb, lips, or tongue without any concomitant motor activity. When stimulation intensity was increased, patients believed that they had actually moved or talked, but again no muscle activity was detected. When, however, the premotor region of the frontal lobes was stimulated, real complex multijoint movements were induced. However, patients did not experience these movements as produced by a conscious internal act of will. Indeed, they were not even aware that they had moved. Increasing stimulation intensity increased the amplitude or complexity of the movement but never made it reach consciousness.
Abstract
Parietal and premotor cortex regions are serious contenders for bringing motor intentions and motor responses into awareness. We used electrical stimulation in seven patients undergoing awake brain surgery. Stimulating the right inferior parietal regions triggered a strong intention and desire to move the contralateral hand, arm, or foot, whereas stimulating the left inferior parietal region provoked the intention to move the lips and to talk. When stimulation intensity was increased in parietal areas, participants believed they had really performed these movements, although no electromyographic activity was detected. Stimulation of the premotor region triggered overt mouth and contralateral limb movements. Yet, patients firmly denied that they had moved. Conscious intention and motor awareness thus arise from increased parietal activity before movement execution.
