Figure 1.

Functional connectivity computed before and after corpus callosotomy for right- and left-sided seed regions. Seed regions defined in the right hemisphere (first column of each set) were used to generate correlation maps both before (second column) and after (third column) complete transection of the corpus callosum. Seed ROIs were placed laterally in the hemispheres to avoid confusion that might arise because of partial volume averaging associated with ROIs close to the midline. Presurgery, functional connectivity maps using the selected seed regions revealed a pattern of correlations that is consistent with published literature, including near symmetric correlations with the contralateral hemisphere. For example, a seed in right lateral parietal region demonstrates correlations with the left lateral parietal as well as with medial prefrontal cortex and posterior cingulate/precuneus (second row). Postsurgery, contralateral correlations that were present before transection prominently disappear (FEF, top row; LP, second row; V1, third row). Correlations with the hippocampal formation seed and the somatomotor seed do not show complete loss of contralateral correlations. These regions have neuroanatomical connections with the opposing hemisphere through fibers that do not cross in the corpus callosum. The temporal lobe, for example, is able to communicate with the contralateral hemisphere through the anterior commissure (Schmahmann and Pandya, 2006). Findings were similar for both right- and left-sided seeds. FEF, z = 55.5; LP, seed, z = 36.5; V1, z = 12.5; HF, z = −13.5; SM, z = 51.5.