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The aim of this study was to perform a comparative investigation of white matter integrity in patients with prelingual and postlingual deafness; we carried out a tract-based statistical analysis of diffusion tensor anisotropy in eight and ten adults with prelingual and postlingual deafness, respectively. Patients with deafness showed significant decreases in diffusion anisotropy at the right internal capsule, the right thalamus, and the splenium of the corpus callosum as well as within the bilateral superior temporal gyrus (including Heschl gyrus) and right temporal white matter. Furthermore, relative to patients with postlingual deafness, those with prelingual deafness showed lower anisotropy in the right superior temporal gyrus, bilateral temporal white matter, and the genu and anterior body of the corpus callosum. We believe that, in patients with deafness, reception of early auditory stimuli before language acquisition might be more critical to white matter maturation and brain reorganization than the nature of auditory stimuli itself or the duration of disuse. These findings provide the theoretical background for early auditory rehabilitation.

To investigate neuroanatomical correlates of the categorization of laryngeally contrastive phonemes, an event-related functional magnetic resonance imaging was performed during an auditory identification task in which 10 participants were distinguished among the three types of word-initial stop phonemes, either lax, tense, or aspirated. Perception of the aspirated consonant series elicited significantly higher activation in the inferior frontal gyrus as compared with both the lax and tense series, and the tense series showed significantly higher activation in the left superior temporal gyrus in comparison with either the lax or the aspirated series. The results show differential involvement of frontal and temporal lobe language areas for distinct phonemic contrasts, supporting a linguistic feature formulation model that posits variably specified phonological representations for the three-way distinctions.

Diffusion properties of the thalamocortical pathways were compared between 30 schizophrenic patients and 22 healthy age-matched and sex-matched volunteers. T1-weighted and diffusion tensor images were used for cortical parcellation and probabilistic tractography to generate population-based thalamocortical pathway maps. The weighted fractional anisotropy and the longitudinal and transversal diffusivity of each pathway were calculated for individual participants. Patients with schizophrenia demonstrated decreased anisotropy and increased longitudinal and transversal diffusivity within the pathways from the mediodorsal nucleus and the pulvinar to the orbitofrontal and parietal-occipital-temporal lobes. Anisotropy decreases and diffusivity increases were correlated with positive and negative syndrome scale scores. Alterations in global diffusion properties within the thalamocortical pathways imply the disruption of brain circuitry in schizophrenic patients.

In order to assess underlying structural differences between the male and female corpus callosum, the fractional anisotropy and volume of the corpus callosum, and also its T1 signal intensity, were measured. The corpus callosum of the 15 normal women and 15 normal men was drawn on the mid-sagittal T1-weighted image, for determining its volume and signal intensity, and this region of interest was projected onto the coregistered fractional anisotropy image, in order to obtain the value for the corpus callosum. We found increased T1 signal intensity and decreased fractional anisotropy in the female corpus callosum, as compared with that of the male. Despite the long-standing debates, the corpus callosum remains a region of sex differences.

To explore the effects of white matter in the absence of auditory input in the early deaf, we conducted a tract-based statistical analysis of the diffusion tensor anisotropy and the voxel-based morphometry in the white matter of 13 early deaf and 29 hearing individuals. Deaf individuals showed significant decreases in diffusion anisotropy and in regional volume reductions within the temporal white matter. Decreased anisotropy was also found at the internal capsule, superior longitudinal fasciculus, and the inferior frontal white matter. In contrast, the forceps major of the corpus callosum, where interhemispheric connections between visual cortices exist, showed increased anisotropy. We interpreted these white matter alterations in terms of both disuse-driven atrophy and compensatory plasticity in the early deaf.

We examined whether deficient prefrontal control over the semantic network exists in patients with schizophrenia. Fourteen patients with schizophrenia and 14 healthy controls performed a comparison task, judging semantic congruity according to an abstract category in an event-related functional MRI paradigm. In the control group, prefrontal-temporal networks consisting of the left inferior frontal gyrus and right inferior frontal sulcus converging at the left posterior superior temporal sulcus were identified as activated during semantic demand of incongruence. In the patients with schizophrenia, we observed a loss of the recruitment of the right inferior frontal sulcus and the prefrontal-temporal network. These findings indicate that cognitive modulation of semantic processing may be dysfunctional in patients with schizophrenia.

Critical times of involvement of areas important to working memory were examined both with pitch and audioverbal N-back tasks using single-pulse transcranial magnetic stimulation (TMS). TMS was administered to 12 healthy participants over dorsolateral prefrontal and inferior parietal regions in each hemisphere at four different times after stimulus onset (250, 450, 650, and 850 ms). For the pitch N-back task, interference with working memory, as evidenced by a significant increase in reaction time, was observed with TMS over the right hemisphere regions. In contrast, for the audioverbal N-back task, TMS resulted in significantly increased reaction time only for left inferior parietal TMS delivered 450 ms after stimulus onset. These results imply different hemispheric specializations for pitch and audioverbal working memory.

The neural reorganization of the visual cortex of early blind individuals was evaluated using voxel-by-voxel analysis of diffusion tensor images with regard to the diffusion direction, diffusion anisotropy and diffusivity. Reduced anisotropy and increased diffusivity was found mainly in the visual pathways of 18 early blind individuals as opposed to 25 sighted individuals. Alteration of the diffusion direction was detected not only in the visual pathways but also in nonvisual pathways such as the u fibers of the parietal lobe, the sagittal striatum, the pulvinar and the inferior and superior longitudinal fasciculi. The alteration of regional diffusion direction, reduced anisotropy and increased diffusivity in early blind individuals imply the neural reorganization for functional adaptation to the loss of visual input during the early development period.

Patients with schizophrenia exhibit deficits in semantic processing, which can form the basis of thought disorders. The objective of this study was to explore functional connectivity between the activated areas during semantic processing in schizophrenia. Twelve patients with schizophrenia and 12 healthy controls were studied with [15O]H2O positron-emission tomography during semantic judgment. The expected activation in the left inferior occipitotemporal cortex significantly correlated with several other regional activations in normal study participants, but with no other regional activations in patients with schizophrenia. This finding suggests that schizophrenia involves a disconnection of semantic networks. The resultant distortion in semantic processing may have an impact on thought disorders.