Brain activation in an involuntary human action.

This work investigated human brain activity in healthy subjects during an involuntary movement. The involuntary movement was driven by an involuntary postural aftercontraction of the deltoid muscle of the shoulder which follows the cessation of a prolonged isometric voluntary contraction. Previous authors have suggested that this aftercontraction phenomenon does not involve the cerebral cortex. To test this idea we examined brain activation using functional magnetic resonance imaging (fMRI) during the involuntary movement and during a matched voluntary movement. In contrast to the conjectures of earlier authors, during the involuntary movement there was widespread activation of the cerebral cortex. There were also clear activation differences between conditions. The voluntary movement showed activation of the putamen whereas the involuntary movement showed much greater activation of the anterior cingulate cortex (BA 24/32). There were also some similarities in the brain areas activated under both movement conditions namely in the left hemisphere precentral gyrus (BA 4), the left hemisphere superior parietal lobe (BA 7), and the bilateral superior temporal gyrus (BA 22). Activity was also present in the caudate nucleus, the thalamus, and the cerebellum. The results are discussed in relation to theories of aftercontraction generation and error processing by the anterior cingulate.