Interhemispheric functional connectivity: an fMRI study in two split-brain patients

Resting state networks (RSNs) were most studied using functional magnetic resonance imaging (fMRI). Interhemispheric functional connectivity (FC) appears mostly supported by the corpus callosum (CC) and several studies have investigated this aspect, still not providing conclusive evidence. In this context, patients in whom the CC was resected for therapeutic reasons (split-brain patients) provide a unique opportunity of research. The purpose of this pilot study is to investigate, with resting state fMRI, the interhemispheric FC in two callosotomized patients operated in adult age, and in four healthy control subjects with intact brain. The analysis was performed with fMRI of the Brain (FMRIB) Software Library (FSL); the evaluation of interhemispheric FC and the recognition of the RSNs were performed by using the probabilistic independent component analysis (PICA). The multi-subject analysis on control subjects allowed the identification of three RSNs: medial visual, default mode, and sensory motor. Both patients showed a bilateral brain activation in the medial visual network, comparable with the controls; in the sensory motor and the default mode networks the activation was unilateral, at variance with controls. These results seem to suggest that the brain, during its maturation, builds new subcortical communication pathways, alternative to the CC, which might support interhemispheric FC in case of callosotomy. Further studies are needed to confirm the observations obtained and reported in this preliminary research.