Cerebral Functional Organization Research Articles

Line bisection following hemispherectomy

Two left- and right-hemispherectomized patients with contralateral hemianopia and 20 normal controls were administered a line bisection task. All hemispherectomized patients showed a strong bisection bias towards their blind visual field. This contralateral bias persisted when patients were forced to start scanning within their blind hemifield, supporting the idea of a strategic adaptation of attention towards the blind visual field. In all patients the hemispherectomy was performed as a result of cortical abnormality (congenital or acquired) and therefore early changes in functional cerebral organization may have occurred in these patients. The absence of a neglect-like ipsilateral bias and the presence of a hemianopic-like contralateral bias in line may represent a functional deficit or suggest that plastic changes following hemispherectomy induced an adaptive functional re-organization of spatial attention in both left- and right-hemispherectomized patients.

Inter- and intrahemispheric EEG coherence during light drowsiness.

The present study was conducted to examine inter- and intrahemispheric EEG coherence in 14 healthy, right-handed adults during wakefulness and light drowsiness as assessed by eye movement and EEG activity. Interhemispheric coherence was significantly lower during light drowsiness than during wakefulness for O1-O2 in the alpha-1 band and for F3-F4 in the beta-1 band. Intrahemispheric EEG coherence was significantly higher during light drowsiness for C4-O2 in the theta-1 and beta-1 bands. These findings indicate that light drowsiness can alter both inter- and intrahemispheric EEG coherence when compared with wakefulness, suggesting that cerebral functional organization changes during light drowsiness. It is important, therefore, to control arousal level of subjects in future studies dealing with the relationship between EEG coherence and various pathological conditions.

Literacy and hemispheric specialization for language: dichotic listening in young functionally illiterate men.

The functional cerebral organization of young men who were defined as illiterate was studied by testing their dichotic listening for language stimuli. These functionally illiterate men showed greater right ear advantage for language stimuli than 50 educated subjects, a pattern already observed with completely illiterate persons of both sexes. This finding is consistent with the view that mastering written codes for language might be one of the most relevant parameters in hemispheric specialization when language is studied.

Auditory evoked potentials and hand preference in 6-month-old infants: Possible gender-related differences in cerebral organization.

Normal 6-month-old infants (10 male and 10 female) were studied to determine if cortical auditory evoked potentials recorded to probe stimuli during verbal and musical stimulus presentation provided an index of cerebral functional organization. Furthermore, evoked potential left-right amplitude asymmetries were examined in relation to gender differences and hand-reaching preference in these infants.

Correlation Between Eeg and Cognitive Abilities: Sex Differences

EEG activity was recorded during rest in 9 male and 9 female volunteers, aged 23 and 27, from C3, C4, T3, T4, P3, P4, O1 and O2, referenced to the ipsilateral earlobe. In a separate session verbal, spatial and abstract reasoning subtests of the Differential Aptitude Test were administered. Samples of EEG activity of 20.48 s were analysed and the interhemispheric correlation was obtained. Interhemispheric correlation in the alpha band was significantly higher in women than in men at central, parietal and occipital derivations. Significant correlations were found between D.A.T. scores and interhemispheric correlation, positive for women with abstract and spatial aptitudes in the central cortex, and negative for men with spatial, abstract and verbal scores in most derivations recorded. The opposite sign of men and women's correlations suggests the existence of a different cerebral functional organization, women showing lower hemispheric differentiation than men.

Language lateralization in children with benign partial epilepsy.

To investigate the relationship between epilepsy and hemispheric asymmetries for language, a dual-task procedure was used to assess language lateralization in children with benign rolandic childhood epilepsy. In the sample selection, care was taken to include factors believed to influence both the mental capabilities of epileptic patients and the individual functional cerebral organization. Results suggest that the interhemispheric prevalence pattern is related to the focus site. Controls as well as epileptic patients with a right hemispheric focus showed the expected left language lateralization; conversely, children with a left unilateral focus showed a different pattern of functional representation, suggesting an involvement of the right hemisphere in language mechanisms. It is emphasized that this atypical cerebral organization is found in subjects with no structural lesion and no therapy. It seems likely that the presence of a focal epileptic activity itself can alter the cerebral mechanisms underlying cognitive functions. A relationship between this modified hemispheric specialization and subtle neuropsychological dysfunctions observed in the children with focal epilepsy is suggested.

Hemispheric specialization for language in the congenitally blind: The influence of the Braille system

The functional cerebral organization of two groups of congenitally blind persons of different age and schooling was studied by testing their dichotic listening to pairs of digits. The younger congenitally blind group showed a comparable level of performance to their control counterparts; however, older subjects shifted their initial right ear advantage to an increased left ear performance as they progressed in the mastery of the Braille system. As this system is founded on spatial strategies, we can concluded that this shift is related to the activation of some right hemispheric linguistic mechanisms.

Cerebral functional asymmetry and MBD children: a synergistic deficit of hemispheres?

The functional cerebral organization of minimal brain-damaged (MBD) children was studied by testing tactile-visual matching of concrete objects. The results revealed that left hand performance was significantly better than the right in the MBD children while normal controls showed no hand difference, and overall performance level was poor for MBD children. These findings are consistent with the view that tactile matching of concrete objects requires hemispheric synergy and that MBD children lack this synergy.

Unilateral right cerebral representation of reading in a familial left-hander

Several recent hypotheses of cerebral functional organization in natural left-handers hold that language, including reading, is localized either unilaterally in the left hemisphere or bilaterally, but not unilaterally in the right hemisphere. A case of alexia without agraphia in a left-hander with an infarct in the right occipital lobe and splenium of the corpus callosum is reported. That a permanent and complete alexia resulted from a single, right hemisphere lesion indicated that reading was completely lateralized to that hemisphere. The case demonstrates that in some natural left-handers language functions can be unilaterally represented in the right hemisphere.

Literacy and hemispheric specialization for language: Digit dichotic listening in illiterates

The functional cerebral organization of illiterate subjects was studied by testing their dichotic listening of pairs of digits. It was found that illiterates show greater right ear advantage for language stimuli than educated control subjects. This finding is consistent with the view that the acquisition of reading and writing skills results in an ambi-hemispheric representation of strategies (mechanisms) for the solution of some language problems.