Crossed avoiding reaction: a disturbance of the manual spatial function.

A patient with MRI confirmed lesions in the corpus callosum and the left cingulate gyrus had a rare syndrome of crossed avoiding reaction of the left hand. With the right hand she could reach a stimulus object in whatever space it was presented. With the left hand, however, she could not mobilise it to reach a stimulus presented in the right hemispace relative to her body axis. In the left hemispace relative to her body axis her left hand reached an object without any difficulty. This left unilateral difficulty in the right unilateral space may be related to a unique spatial function that controls manual space, which is represented differentially in the two hemispheres. In the left hemisphere this function covers bilateral hemispace and is operated by the right hand. In the right hemisphere this function covers only the left hemispace and is operated by the left hand.