Callosal syndrome: implications for understanding the neuropsychology of stroke.

A case is presented of callosal syndrome following cerebral hemorrhage and amphetamine abuse in a 26-year-old right-handed man. There were few hemispheric findings but a full callosal syndrome including left apraxia to verbal commands, left tactile anomia, left agraphia, right constructional apraxia, failure of blindfolded side-to-side hand replication and form-board testing showing loss of interhemispheric transmission including intermanual interference. The "draw-a-clock" test showed left inattention when drawn with the right hand but not the left, and perseveration was noted for spatial tasks done with the right hand and symbolic tasks done with the left. The patient recovered functionally almost completely but testing demonstrated continued loss of interhemispheric transmission. The case is considered of most interest for its potential in explaining phenomena observed in severe unilateral hemispheric lesions. Our findings suggest that perseveration is not a dysfunction of the damaged portion of the brain, but a phenomenon associated with intact brain attempting unfamiliar tasks. The persistence of left hemi-inattention is attributed to the inability of the left hemisphere to utilize spatial information to compensate for the phenomenon of inattention. Left-sided dyskinesia following left hemisphere lesions was attributed to the lack of symbolic information necessary to perform some movements. Dysprosody was attributed to lack of tonal information to the left hemisphere. Recovery of function following severe unilateral lesions may be largely due to compensatory learning by the intact hemisphere and assertion of ipsilateral control. As our patient originally assumed an inverted left-handed writing posture, we assume the posture is controlled by the right hemisphere.(ABSTRACT TRUNCATED AT 250 WORDS)