Guy Geoffroy

Absence of disconnexion syndrome in callosal agenesis and early callosotomy: Brain reorganization or lack of structural specificity during ontogeny?

Four acallosal subjects, one child, aged 5, and three adults, as well as five epileptic patients who underwent callosotomy between the ages of 6-21 years, were tested on a variety of intra- and intermanual tasks in a study aimed at elucidating the developmental aspects of callosal plasticity. The performance of the clinical sample was compared to that of 48 normal children, aged 5-12 years, an age span generally considered to coincide with the final stages of callosal maturation. As previously reported, interhemispheric integration improved with increasing age in the normal sample. The two patients having undergone callosotomy in childhood performed as well as their normal peers, whereas the three others who had the operation in late adolescence or adulthood showed the typical disconnexion deficits reported in the literature. The acallosal subjects, including the youngest one, outperformed all groups. We speculate that the remarkable plasticity seen in the acallosals and the young callosotomized patients may be related to a critical period in development coinciding with a phase of synaptic overproduction and redundancy that would favor the reinforcement of alternative neural pathways. The compensatory mechanisms appear to become more limited in late adolescence when synaptic distribution presumably assumes adult patterns.

Corpus callosotomy for control of intractable epilepsy in children

cerebral commissurotomy has often been reported to control seizures in patients suffering from intractable epilepsy. HIowever, in adults, division of the corpus callosum alone has been shown to be equally effective while considerably reducing the surgical morbidity. The present study of nine epileptic callosotomized patients suggests that callosal section can also be performed successfully and safely in children. Neurologic and concomitant psychological improvements are described.

Extent and limits of cerebral adjustment to early section or congenital absence of the corpus callosum.

The ability to effect inter- and intrahemispheric comparisons of visual and tactile stimuli was studied in 4 callosotomized patients and 6 callosal agenesis subjects using response accuracy and response times to determine the extent of cerebral adjustment to functional or congenital absence of the corpus callosum. The visual tasks involved within- and between-fields presentation of pairs of colours and shapes. The tactile tasks required uni- and bimanual comparisons of 3 categories of stimuli (size, shape and texture) of increasing difficulty. Older callosotomized children showed disconnection deficits similar to those reported in adult split-brain patients, whereas both acallosal subjects and our youngest patient with complete callosal transection demonstrated a high level of accuracy in the interhemispheric tasks. However, all patients required considerably more time to accomplish the cross-integration of relatively complex visual and tactile information which seems to be one of the major limitations of the compensatory mechanisms. The results also indicate that the quality of transfer differs between the acallosal and early-callosotomized patients in relation to the sensory modality studied. Thus, visual cross-matching was found to be superior to bimanual matching for the callosotomized group, whereas intermanual comparisons proved to be more efficient than visual integration in the acallosals. These divergent findings suggest not only that different compensatory mechanisms may be operating in visual and tactile transfer, but also that the same mechanisms may be utilized differently by the two populations deprived of the use of callosal connections.

Interhemispheric integration of sensory and motor functions in agenesis of the corpus callosum.

Abstract Two siblings with total agenesis of the corpus callosum were compared with matched epileptic and normal controls on bimanual integration of kinesthetic, somesthetic and motor functions. No differences were found between acallosals and control subjects on any of the transfer tasks. However, the acallosal patients were impaired in bimanual operations with regard to speed. The deficit was more pronounced in the younger subject who also showed impairment of differentiated finger movements. Bilateral organization of speech and cross-cuing strategies could have accounted for facilitated performance on some but not all of the transfer tasks. Increased use of ipsilateral and/or subcortical pathways are a more plausible and more parsimonious explanation for the results of this study.

Sound localization in hemispherectomized patients

In order to precisely evaluate the consequences of cortical damage on free-field sound localization in humans, the present study examined response accuracy to auditory targets in three hemispherectomized patients and IQ-matched controls. Listeners reported sound location by pointing with their dominant hand to the apparent sound location in an anechoic chamber. Two conditions were tested: (i) localization of a fixed-sound source and (ii) localization of the beginning and the end of a simulated moving stimulus. In both conditions, the responses of the patients were less accurate than those of the controls in the hemifield contralateral to their removed hemisphere. Moreover, the single-case analyses revealed that the performances obtained with fixed sources were generally more precise than those obtained with moving sources. This result is discussed in terms of a differential involvement of cortical and subcortical pathways in the processing of stationary and moving sounds. Finally, the age at surgery and the post-surgical interval were related with the magnitude of the deficits, suggesting the possible influences of functional reorganization and cerebral plasticity.

Auditory lateralization for speech in language-impaired children

The ability of five language-impaired (LI) children and five matched controls, aged 7-10 years, to discriminate natural pairs of consonant-vowel syllables contrasted on place of articulation and voicing, presented to the right or left ear with white noise in the contralateral ear, was investigated. The general pattern of errors indicated that LI children had more difficulty than controls in discriminating place of articulation contrasts only when they were presented to the left ear, as well as a difficulty in discriminating voice contrasts selective to the right ear. The results are discussed in terms of acoustic integration and suggest that bihemispheric dysfunction is a basis for specific language impairment.

Hemispheric asymmetry in callosal agenesis as revealed by dichotic listening performance

Abstract Two patients with total callosal agenesis were compared with two control groups on a dichotic listening task using verbal and non-verbal stimuli. Acallosal patients displayed left ear superiority and abnormally long reaction times regardless of the nature of the stimulus. The results are interpreted in terms of hemispheric reorganization in acallosal patients.

Childhood visual agnosia: A seven-year follow-up

Abstract We describe the case of a child who developed an associative visual agnosia and document her neuropsychological and neuroimaging progression over the past 7 years. AR contracted a viral encephalitis at age 9 that destroyed the right temporal lobe and a portion of the left inferotemporal region. A triad of symptoms was observed: associative visual agnosia, prosopagnosia and color agnosia. With time, AR has shown limited behavioral improvement. Neuroimaging showed that, apart from the initial ‘normal’ findings, the neuroanatomical correlates remained stable over time. Strikingly, a clear dissociation between object and spatial representations is present in this patient, which is the basis for her apparent recovery of function. Indeed, she uses spatial as well as local cues to compensate for her recognition deficits. ARs inability to recognize objects is interpreted as a deficit in the inferior temporal ventral pathway specialized for object perception, whereas the posterior parietal dorsal pathway...

Absence of Disconnection Syndrome after Early Callosotomy

Ever since the seminal studies of Sperry, Gazzaniga and Bogen (e.g., Sperry et al. 1969) it is well established that epileptic adults with therapeutic section of the corpus callosum show interhemispheric disconnection deficits. Typically, these patients are unable to compare sensory information separately conveyed to different hemispheres. This applies particularly to the visual and tactile modalities that are based upon predominantly crossed pathways.

Neuropsychological and Psycho-social Consequences of Corpus Callosotomy

Groupe de Recherche en Neuropsychologie Experimentale Departement de Psychologie Universite de Montreal C. P., 6128, Succ. Centre-Ville Montreal, Que. H3C 3J7, Canada Departement de Pedopsychiatrie Hopital Neurologique et Neuro-chirurgical Pierre Wertheimer 69394 Lyon Cedex 03, France Departement de Psychologie Universite de Montreal C. P., 6128, Succ. Centre-Ville Montreal, Que. H3C 3J7, Canada Service de Neurologie Hopital Sainte-Justine 3175 Ch. Cote Sainte-Catherine Montreal, Que., H3T 1C5, Canada Service de Neurochirurgie Hopital Sainte-Justine 3175 Ch. Cote Sainte-Catherine Montreal, Que., H3T 1C5, Canada