Neuropsychological alterations after split-brain surgery.

Neuropsychological changes following corpus callosotomy depend on the degree of the callosal section, the portion sectioned and the patient's age at the time of the surgery. Anterior section frequently results in transient hemiparesis of the non-dominant leg and temporary difficulties in initiating speech. Posterior section is followed by disconnection symptoms in the sensory modalities which can be demonstrated when input is lateralized and one hemisphere is denied access to the information received by the other. Visual and tactile stimuli presented to the non-dominant hemisphere are no longer verbally identified due to disconnection from the language-dominant hemisphere. Total callosotomy additionally interrupts interhemispheric communication between the motor regions. This results in deficits in bimanual coordination and apraxia of the non-dominant hand to verbal commands. Some of the symptoms subside, probably due to increased use of ipsilateral sensory and motor pathways. Others are permanent. However, they are not disabling since unrestricted scanning of the environment ensures bilateral representation of sensory experience. Cognitive functions are frequently improved, although preexisting lateralized deficits may be exacerbated. Learning of new material is difficult for some patients with lateralized temporal lobe dysfunction in whom interhemispheric compensation is abolished by the surgery. Language deficits are observed mainly in patients with crossed dominance. Studies in children reveal that callosotomy performed before puberty is not followed by permanent disconnection deficits. This may be attributable to the greater neural plasticity of the immature brain.