Callosal plasticity and interhemispheric transfer

It is generally well accepted that cerebral lesions occurring early in life (before the so-called critical period) result in anatomical reorganization and consequently in functional recovery. Studies carried out in young patients who have undergone a callosotomy for intra-tractable epilepsy or in patients with callosal agenesis have demonstrated the absence of the disconnection syndrome reported in commissurotomized adult patients (reviewed by Lassonde et al., 1990). The young calloso-tomized patients and those with callosal agenesis could perform tactile and visual interhemispheric tasks without any difficulty. These results suggest that in the absence of the corpus callosum in young individuals, extracallo-sal commissures could undergo anatomical reorganization and facilitate interhemispheric communication. We have tested (Ptito and Lepore, 1983) whether the inter-hemispheric transfer of visual information is possible

Discriminations

Figure 6.5. Bar charts illustrating the learning and retention performance for pattern discriminations following the various surgical interventions. LOT: Trials to criterion for learning a pattern discrimination following the left optic tract section in group 1. LOT + RVA: Trials to criterion after an additional lesion of the visual cortical areas of the right hemisphere for the relearning of the previously acquired pattern discrimination and learning of a new one (group 1) and for initial pattern discrimination learning (group 2). LOT + RVA + CC: Trials to criterion for the relearning of one pattern discrimination and learning of a new one following the additional section of the corpus callosum for both groups. Note the improved performance not only for the relearning of previously learned discriminations but also for learning a new one following the callosotomy. (Adapted from Ptito et al., 1993.)

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