Ipsilateral auditory extinction following frontal and basal ganglia lesions of the left hemisphere.

When tested on a dichotic digits listening task, patients with unilateral lesions of the left frontal lobe and left anterior basal ganglia exhibited ipsilateral auditory extinction. This phenomenon has been documented before, but only in patients with lesions involving the region posterior and lateral to the posterior aspect of the left lateral ventricle. As patients with lesions in the equivalent region of the right hemisphere also exhibit extinction of verbal material arriving in their left ears it has been hypothesized that these posterior lesions disrupt an interhemispheric pathway connecting the two temporal lobes. As it appears that the ipsilateral auditory pathways are suppressed under conditions of dichotic stimulation, such an interhemispheric pathway would be the means whereby left-ear verbal stimuli reached the left (speech) hemisphere. Therefore a disruption of this pathway could result in left-ear extinction for verbal material. The finding that left anterior lesions also result in left-ear extinction poses problems for this hypothesis and in particular for the suggested posterior route of the interhemispheric pathway.