Detecting interhemispheric transfer across the corpus callosum using high field functional magnetic resonance imaging

Interhemispheric transfer (IT) across the corpus callosum was investigated using high field functional magnetic resonance imaging (fMRI) and an innovative experimental design. Functionally lateralized stimuli (words: left hemisphere; faces: right hemisphere) were presented using visual hemifield stimulation in order to manipulate visual IT. In addition, motor IT was manipulated by varying response hand. As expected, visual IT was associated with decreased accuracy; however, there were no behavioural correlates of motor IT. Task-related fMRI activation was observed in a distributed network, including bilateral inferior and superior parietal, medial frontal/cingulate, middle/inferior frontal, fusiform, cerebellum, and sub-cortical regions. At the group level, activation specific to IT (i.e., crossed > uncrossed activation) was observed, but only at liberal thresholds. Interestingly, corpus callosum activation was observed for a subset of participants (60%), reflecting prominent inter-individual differences in interhemispheric transfer. The ability to detect white matter activation will ultimately expand the scope of fMRI research.