The general pattern of hippocampal functional connectivity among healthy individuals included stronger bilateral hippocampal and greater connectivity in the septal neuclei near the anterior commissure than the septal neuclei, as compared to patients. In contrast, the pattern of hippocampal connectivity among patients with TAI demonstrated reduced contralateral strength of correlation, but generally preserved correlation ipsilaterally, and greater correlation in the subthalamic nuclei near the posterior commissure, parahippocampal gyrus, and posterior cingulate cortex than controls. Although contralateral hippocampal connectivity was significantly reduced among patients, it was not absent. This is consistent with a prior report of functional connectivity before and after a complete surgical corpus callosotomy.49 Their observation of limited interhemispheric connectivity despite the complete transection of the main commissural fiber suggests that interhemispheric connectivity also occurs through other commissural fibers such as the anterior and/or the posterior commissures. Patients in the present study undoubtedly underwent varying degrees of subcortical white matter injury including injury to the CC, as evidenced by FLAIR MRI (see inclusion criteria); therefore, they presumably have varying degrees of healthy callosal axons allowing some (albeit reduced) functional
