Hemispheric specialization using SPECT and stimulation tasks in children with dysphasia and dystrophia.

Developmental dysphasia, a severe childhood learning disorder, is thought to result from problems in hemispheric specialization involving both left and right cerebral hemispheres. Regional cerebral blood flow (rCBF) was measured at rest and during stimulation of both hemispheres independently: dichotic listening for the left, dichaptic palpation for the right. Eight right-handed boys with expressive dysphasia, aged 8 to 12 years, were investigated using SPECT and compared with eight right-handed age-matched boys with Duchenne muscular dystrophy with reading disorders but normal speech. rCBF values at rest were also compared with those of five right-handed age-matched normal boys. In the dichotic task, children with dysphasia differed from children with dystrophia by failure to increase rCBF in the left hemisphere, in Broca's area, but rCBF increased in the right hemisphere, in the region homologous to Broca's area. In the dichaptic task, rCBF increased bilaterally for children with dysphasia whereas in children with dystrophia rCBF increased only in the right hemisphere. At rest the physiological asymmetry was reversed in favor of the right hemisphere in all areas except Broca's area. Surprisingly, the same applied at rest and for all areas in children with dystrophia. These results confirm that functional specialization of both hemispheres is impaired in developmental dysphasia. Moreover, they suggest that learning disabilities associated with Duchenne muscular dystrophy could also be related to abnormal hemispheric specialization.

[Impairment of visual recognition after a traumatic brain injury]. / Evolution des troubles de la reconnaissance visuelle à distance d'un traumatisme cérébral.

Impaired vision and cerebral blindness were observed in a patient who had suffered brain trauma. One year after the trauma, the impairment was characterized by low visual acuity, visual field restricted to central tunnel vision and impaired recognition of objects, line drawings, colors and faces. Vision improved six years after the brain trauma with more rapid recognition of objects and line drawings, increased visual acuity and broadening of the visual field. Reading was possible at this time. However, prosopagnosia remained very severe and was still the primary complaint of the patient. Improvement of visual function continuing for several years after a brain injury is discussed on the basis of cognitive and neurophysiological knowledge. The place of rehabilitation is discussed. Functional improvement is explained by extrastriate cortical afferences and the cortical network of visual pathways.

Three-dimensional reconstruction of the human central sulcus reveals a morphological correlate of the hand area.

One way to improve our understanding of cortical anatomy is to visualize the three-dimensional (3D) shape of the cerebral sulci which is normally hidden. Here, we reconstructed the 3D morphology of the central sulcus (CS) in 17 normal subjects, using conventional magnetic resonance images and dedicated software. We found that the 3D morphology was remarkably consistent in all central sulci. Our analyses revealed three different regions (upper, middle and lower), which were easily identifiable by morphological criteria and sharply interconnected in the reconstructed CS. These morphological regions appear to have a strong functional significance, since the middle region corresponded precisely to the 'hand area', as verified by hand vibration positron emission tomography activation studies in eight cases. These data suggest that the 3D anatomy of the cerebral cortex may facilitate sulcal recognition, and sulcal subdivision into smaller morphological elements, bearing remarkable relationships with functional cortical maps.

Lateralization of speech and auditory temporal processing.

To investigate the role of temporal processing in language lateralization, we monitored asymmetry of cerebral activation in human volunteers using positron emission tomography (PET). Subjects were scanned during passive auditory stimulation with nonverbal sounds containing rapid (40 msec) or extended (200 msec) frequency transitions. Bilateral symmetric activation was observed in the auditory cortex for slow frequency transitions. In contrast, left-biased asymmetry was observed in response to rapid frequency transitions due to reduced response of the right auditory cortex. These results provide direct evidence that auditory processing of rapid acoustic transitions is lateralized in the human brain. Such functional asymmetry in temporal processing is likely to contribute to language lateralization from the lowest levels of cortical processing.

Time course of prefrontal lobe dysfunction in severely depressed in-patients: a longitudinal neuropsychological study.

The Stroop Colour-Word Test (SCWT) and the Verbal Fluency Test (VFT), two tests that have been suggested to be particularly sensitive to prefrontal dysfunction, were administered to 23 severely depressed in-patients. Both tests were impaired in patients at inclusion, but only verbal fluency normalized with successful treatment of depression. VFT impairment is consistent with the hypothesis of a left prefrontal cortex dysfunction in depression. Moreover, the persistence of an impaired performance on SCWT in patients at discharge suggests that a selective attention deficit may persist in patients beyond a clear clinical improvement.

Brain metabolism after recurrent insulin induced hypoglycaemic episodes: a PET study.

Neuropsychological testing was carried out and the rate of oxygen metabolism in the brain was measured by PET in 15 highly selected patients with type 1 diabetes. The aim was to investigate the impact on the brain of hypoglycaemic comas resulting from insulin treatment. No significant difference was found between nine patients with a history of more than 10 hypoglycaemic comas and six others who denied any history of such events. These data suggest that intensified insulin treatment, although increasing the frequency of hypoglycaemic coma, may not always be harmful for the brain. This may be explained by the limited duration of hypoglycaemic coma induced by conventional insulin treatment.

Person identification and self-concept in the delusional misidentification syndrome. A case study.

This study on a delusional misidentification patient with both Frégoli symptoms and intermetamorphosis investigates the cognitive structure of others and of the self-representations with a new clustering method (HICLAS conjunctive model). Results show that this patient, free from face recognition disorders, shows severe structural anomalies in the mapping of misidentified others, and of the self. Disturbances in the cognitive structure and person identification are discussed in reference to a psychopathological explanation of the misidentification syndrome.

Delusional misidentification: a clinical, neuropsychological and brain imaging case study.

The case of a young woman with a disorder involving Capgras syndrome, Frégoli syndrome, intermetamorphosis, and the subjective-doubles syndrome is reported. Neuropsychological assessment showed a low efficiency in the complex visuospatial organization tasks and in non-verbal memory. MRI found a left lenticular hypodensity, and two PET scans performed in the symptomatic and recovered states showed significant changes and asymmetries in cerebral glucose metabolism in the frontal, parietal, and subcortical regions. These findings are discussed with respect to recent models of delusional misidentification syndromes.

Changes in regional cerebral blood flow during brain maturation in children and adolescents.

Regional cerebral blood flow (rCBF) was studied by SPECT using 133Xe in 42 children, aged 2 days to 19 years, considered as neurologically normal. rCBF was measured on cortical regions and on the cerebellum and thalamus. Curves for reference values and standard deviation were defined for each region. At birth, cortical rCBFs were lower than those for adults; after birth they increased until 5 or 6 yr of age to values 50%-85% higher than those for adults and thereafter decreased, reaching adult levels between 15 and 19 yr. Neonatal values of rCBF on cerebellum and thalamus were slightly higher than adult level, but not significantly; after age 1, they followed the common pattern for cortical curves. When rCBFs were expressed in percent global CBF, they were lower at birth than adult levels in the cortex, then increased and reached a plateau corresponding to the adult value before the second year of age. The time needed to reach normal adult values differed for each cortical region. The shortest time was found on the primary cortex and the longest on the associative cortex. Cognitive development of the child seems to be related to changes in blood flow of the corresponding brain regions.

Visuospatial performance in left-handed patients with unilateral brain lesions.

A test of visuospatial judgment was given to left-handed patients with lesions of either the right or left hemisphere. In right-handed patients impaired performance on the test has been found to be almost exclusively associated with right hemisphere disease, the performance of patients with left hemisphere disease being comparable to that of controls. The left-handed patients in this study showed the same performance pattern: a high proportion of patients with right hemisphere lesions performed defectively while all the patients with left hemisphere lesions performed on a normal level. Thus the findings are in accord with the conclusion that hemispheric cerebral organisation with respect to the mediation of visuospatial performance do not differ in right-handers and left-handers.