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Developmental dyslexia is a frequent language-based learning disorder characterized by difficulty in reading. The predominant etiologic view postulates that reading impairment is related to phonological and orthographic dysfunction. The aim of this fMRI study was to evaluate the neural bases of phonological processing impairment in remediated dyslexic adults (DD). We used a rhyming words judgment task contrasted with an unreadable fonts font-matching judgment task to compare patterns of activation and functional asymmetry in DD and normal-reading young adults. We found evidence of a link between asymmetry in inferior frontal gyrus and performance during the phonological processing. We also observed that DD recruit a network including regions involved in articulatory control in order to achieve rhyme judgment suggesting that, due to a lack of hemispheric specialization, DD recruit the latter network to achieve rhyme judgment., (Copyright © 2013 Society for Psychophysiological Research.)

Introduction: The aim of this study was to evaluate whether the classic asymmetry seen in hemispheric functioning is modified in older adults by using a verbal-manual concurrency task., Method: Thirty-five right-handed participants divided into two groups according to age (15 older participants, mean age: 68 ? 8 years, without cognitive decline and 20 younger participants, mean age: 23 ? 2 years) had to perform a 30-second uni-manual tapping task, in both a single task (tapping alone) and dual task (tapping and performing a letter fluency task together) condition., Results: In younger participants, the letter fluency task disrupted the right hand more than the left hand whereas, in older participants, the letter fluency task disrupted both hands equally., Conclusion: These results should be considered preliminary data using a behavioral dual task condition, which might be useful for studying lateralized hemispheric functioning and the processes of divided attention during aging.

Dichotic listening is the most frequent behavioral test used to assess hemispheric lateralization. The subjects simultaneously receive competing information signals in each ear and the attention resources are mobilized. Dichotic listening may be viewed as a dual-task procedure. In fact, executive functions and attention, which are involved, may be modified in elderly. The aim of this paper is to define the role of dichotic listening for the study of hemispheric interactions in the elderly, according to compensation/reorganization processes in normal and pathological aging.

Cerebral hemispheric lateralization is an old concept, particularly concerning language. In children, numerous arguments favour a left hemispheric predisposition for language, but do not exclude its strengthening during childhood. In the elderly, changes in the lateralization have been described. Two models were proposed to explain these changes. The right hemi-aging model is supported by behavioral studies and the age-related asymmetry reduction model is documented by brain imaging studies. We review the data supporting the two models. The significance of this age-related asymmetry reduction is questionable. The dedifferentiation view suggests that bilateral activation in older adults reflects difficulty in recruiting specialized neural mechanisms. Age-related asymmetry reduction may also be evidence of compensatory mechanisms and plasticity of the aging brain. It is useful for understanding physiopathology of cognitive decline and rehabilitation potential of the aging brain.

Although Benign Childhood Epilepsy with Centrotemporal Spikes (BECTS) has a good prognosis, a few studies have suggested the existence of language disorders relating to the interictal dysfunction of perisylvian language areas. In this study, we focused on language assessment in 16 children aged 6-15 currently affected by BECTS or in remission. An important proportion of children showed moderate or more severe language impairment. The most affected domains were expressive grammar and literacy skills. We found linguistic deficits during the course of epilepsy but also persistent deficits in children in remission, suggesting possible long-term effects. Our results support the hypothesis that BECTS may be associated with impairment to language and suggest the possibility of a direct link between epileptic activity and language development, and the existence of long-term consequences.

The functional specialization of each hemisphere in adults is now well accepted. Neuropsychology of hemispheric functioning in young children is a more debatable issue and must take into account additional factors such as development and maturation, characterized by complex changes in anatomy and organization. The first part of this review describes the theory behind the development of the functional organization of the brain. Second, we discuss data regarding brain lesions in children with brain damage and with normal development. We comment on the concept of plasticity and the critical period. We also discuss the neurobiological processes underlying the functional organization of the brain in the model of developmental disorders in children. We chose three disorders involving the left hemisphere (developmental dysphasia), both hemispheres (benign rolandic epilepsy) or the right hemisphere (congenital hydrocephalus) in order to examine their relationship to a specific hemispheric functional organization. We used classic neuropsychological tests such as the dichotic listening task, the dichaptic palpation and the time-sharing paradigm. The patterns observed in each pathology are discussed in light of data obtained in children with brain lesions.

Spectral analysis of the EEG alpha rhythm was studied in nine temporal epileptic right-handed patients in order to predict localization of the speech area. We studied the variation of the spectral power of the alpha rhythm during an activation paradigm previously validated in normal right-handed subjects. Significant alpha power decreases in the left hemisphere during writing with the right hand (as compared to resting) and/or significant alpha power decreases in the right hemisphere during left-hand recognition and classification of cardboard objects (as compared to resting) were considered as consistent with left-hemisphere dominance for language. The results of EEG spectral analysis were compared with those of the Wada test. The left hemisphere was dominant for language according to the Wada test in eight subjects and the right hemisphere in one subject. Six patients had a significant alpha power reduction in the hemisphere concerned during lateralized cognitive tasks, consistent with language localization in the left hemisphere according to the Wada test. The three remaining patients had no significant EEG spectral power variations. A significant decrease of alpha power in the active hemisphere during cerebral activation seems statistically related to left-hemispheric dominance for language in right-handed subjects (hemispheric specialization). However, the localization of the speech area using this electrophysiological method does not appear clinically relevant for a case-by-case decision in individual patients.

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.

Hemisphere specialization for language was studied in 10 children with expressive developmental dysphasia (DD) (mean age 10 years 4 months) submitted to a dichotic listening task (in a word free-recall task and forced-attention task) and a finger tapping/vocalization dual-task paradigm. A nonsense shape dichaptic task was also introduced to control right hemispheric processing. Performances of dysphasic children were compared to those obtained from 15 normal children. The results showed that controls had a right ear advantage in free-recall (words) dichotic listening task and a significant right ear advantage in forced-right-attention task, with a change in ear asymmetry as a consequence of instruction. In the dysphasic group we observed a significant right ear advantage in the free-recall dichotic listening task and no change in ear asymmetry during forced right or forced left condition. Results in time sharing paradigm and nonsense dichaptic task are more difficult to interpret, because there was no interaction between group and condition. These results cannot support a complete left hemisphere dysfunction in developmental dysphasia.