Ipsilateral cortical representation of tactile and painful information in acallosal and callosotomized subjects.

Previous studies have shown that unilateral painful but not tactile stimulation produces ipsilateral cortical activation in callosotomized patients. Here, we used functional magnetic resonance imaging (fMRI) to compare activation evoked by tactile and thermal pain stimulation in two individuals with callosal agenesis, one callosotomized patient, and six control subjects. Bilateral tactile activation was found in S1 and/or S2 of both hemispheres in control and acallosal subjects whereas no ipsilateral activation was detected in these structures in the callosotomized participant. In contrast, although there was some inter-individual variability in the pattern of responses to pain, all subjects including the callosotomized patient showed ipsilateral responses in at least two of the target pain-related areas (S1, S2, insula and/or cingulate cortex). These findings are consistent with the plasticity of the touch system in callosal agenesis and further confirm that ipsilateral activation of pain-related regions does not require the integrity of the corpus callosum.