Interhemispheric communication after section of the forebrain commissures

Cognitive information is shown to be transmitted interhemispherically through channels other than the neocortical commissures, presumably through subcortical pathways. What crosses through these subcortical channels does not appear to include the name or identity of stimuli but rather is more contextual or associative in nature. Results obtained with a technique for prolonged visual lateralization indicate that this information, when used in conjunction with cognitive strategies, allows the cortically disconnected left hemisphere under certain conditions to verbally identify stimuli projected to the right hemisphere or to cross-compare bilateral input. The presence of this subcortical communication would thus appear to help explain some of the increasing exceptions to characteristic disconnection symptoms reported among split-brain subjects. In particular, the present results challenge reports which have attributed oral naming of stimuli in the left visual hemifield to the typical disconnected right hemisphere.