Rightward hemispheric asymmetries in auditory language cortex in children with autistic disorder: an MRI investigation

Purpose: determine if language disorder in children with autistic disorder (AD) corresponds to abnormalities in hemispheric asymmetries in auditory language cortex. Methods: MRI morphometric study in children with AD (n = 50) to assess hemispheric asymmetries in auditory language cortex. A key region of interest was the planum temporale (PT), which is larger in the left hemisphere in most healthy individuals. Results: (i) Heschl’s gyrus and planum polare showed typical hemisphere asymmetry patterns; (ii) posterior Superior Temporal Gyrus (pSTG) showed significant rightward asymmetry; and (iii) PT showed a trend for rightward asymmetry that was significant when constrained to right-handed boys (n = 30). For right-handed boys, symmetry indices for pSTG were significantly positively correlated with those for PT. PT asymmetry was age dependent, with greater rightward asymmetry with age. Conclusions: results provide evidence for rightward asymmetry in auditory association areas (pSTG and PT) known to subserve language processing. Cumulatively, our data provide evidence for a differing maturational path for PT for lower functioning children with AD, with both pre- and post-natal experience likely playing a role in PT asymmetry

Arcuate Fasciculus Abnormalities and Their Relationship with Psychotic Symptoms in Schizophrenia

Disruption of fronto-temporal connections involving the arcuate fasciculus (AF) may underlie language processing anomalies and psychotic features such as auditory hallucinations in schizophrenia. No study to date has specifically investigated abnormalities of white matter integrity at particular loci along the AF as well as its regional lateralization in schizophrenia. We examined white matter changes (fractional anisotropy (FA), axial diffusivity (AD), asymmetry indices) along the whole extent of the AF and their relationship with psychotic symptoms in 32 males with schizophrenia and 44 healthy males. Large deformation diffeomorphic metric mapping and Fiber Assignment Continuous Tracking were employed to characterize FA and AD along the geometric curve of the AF. Our results showed that patients with schizophrenia had lower FA in the frontal aspects of the left AF compared with healthy controls. Greater left FA and AD lateralization in the temporal segment of AF were associated with more severe positive psychotic symptoms such as delusions and hallucinations in patients with schizophrenia. Disruption of white matter integrity of the left frontal AF and accentuation of normal left greater than right asymmetry of FA/AD in the temporal AF further support the notion of aberrant fronto-temporal connectivity in schizophrenia. AF pathology can affect corollary discharge of neural signals from frontal speech/motor initiation areas to suppress activity of auditory cortex that may influence psychotic phenomena such as auditory hallucinations and facilitate elaboration of delusional content

Asymmetries of the planum temporale and Heschl's gyrus: relationship to language lateralization.

Morphological asymmetries favouring the left hemisphere in the planum temporale (PT) and Heschl's gyrus (HG) have both been presumed to relate to the typical left-hemisphere dominance for language functions. However, a direct link between structure and function has not been clearly established. The present study investigates this issue by measuring the volume of the PT and HG on the MRI scans of epilepsy patients classified into three groups: left speech group (LSG; n = 20), right speech group (RSG; n = 11) and bilateral speech group (BSG; n = 13), as assessed by the intracarotid Sodium Amytal procedure. Additionally, an automatic voxel-based morphometry (VBM) analysis was performed to explore collateral structural asymmetries. Although leftward structural asymmetries were found in the PT, consistent with the literature, they did not relate to language lateralization. For HG we also replicated asymmetries favouring the left side; interestingly, three of the individuals within the RSG showed a strongly reversed asymmetry, but as a whole the structure-function relationship for HG was not obligatory. The VBM analysis revealed a grey-matter concentration difference in the posterior part of the inferior frontal gyrus (pars opercularis, corresponding functionally to Broca's area), which favoured the left hemisphere in the LSG, and the right hemisphere in the RSG. The findings suggest that this frontal cortical region bears a direct relationship to language lateralization, which may be related to use-dependent plasticity in patients with language reorganization

Is the planum temporale surface area a marker of hemispheric or regional language lateralization?

International audienc