Depletion of attentional capacity after total commissurotomy in man.

The attentional capacity of 6 total commissurotomy patients and 2 partial commissurotomy patients was tested by means of a vigilance task in which signals were flashed to the left or right hemisphere. With complete commissurotomy a gross depletion of attentional capacity was discovered which was absent in the partial commissurotomy patients, whose performance equalled that of normal man. Hemisphere asymmetry was also observed. The left hand was more likely to act in the absence of appropriate signals; the left hemisphere showed none of the expected high level efficiency, displaying, instead, a discontinuous action characterized by gaps and holes in its relation to the stimuli. The results are interpreted to mean that some aspect of consciousness represented by sustained attention is dependent upon hemispheric co-operation and upon the integrity of the cerebral commissures.