Abnormal angular gyrus asymmetry in schizophrenia

Abstract

Objective: Few studies have evaluated the parietal lobe in schizophrenia despite the fact that it has an important role in attention, memory, and language-all functions that have been reported to be abnormal in schizophrenia. The inferior parietal lobule, in particular, is of interest because it is not only part of the heteromodal association cortex but also is part of the semantic-lexical network, which also includes the planum temporale. Both the inferior parietal lobule, particularly the angular gyrus of the inferior parietal lobule, and the planum temporale are brain regions that play a critical role as biological substrates of language and thought. The authors compared volume and asymmetry measures of the individual gyri of the parietal lobe by means of magnetic resonance imaging (MRI) scans.

Method: MRI scans with a 1. 5-Tesla magnet were obtained from 15 male chronic schizophrenic and 15 comparison subjects matched for age, gender, and parental socioeconomic status.

Results: Inferior parietal lobule volumes showed a leftward asymmetry (left 7.0% larger than right) in comparison subjects and a reversed asymmetry (left 6.3% smaller than right) in schizophrenic subjects. The angular gyrus accounted for this difference in asymmetry, with the left angular gyrus being significantly larger (18.7%) than the right in comparison subjects, a finding that was not observed in schizophrenic patients. A further test of angular gyrus asymmetry showed a reversal of the normal left-greater-than-right asymmetry in the schizophrenic patients.

Conclusions: Patients with schizophrenia showed a reversed asymmetry in the inferior parietal lobule that was localized to the angular gyrus, a structure belonging to the heteromodal association cortex as well as being part of the semantic-lexical network. This finding contributes to a more comprehensive understanding of the neural substrates of language and thought disorder in schizophrenia.

FIGURE 1. Differential Left-Versus-Right Asymmetry in Inferior Parietal Lobule Volume in Male Patients With Schizophrenia and Healthy Male Comparison Subjects

FIGURE 2. Asymmetry Coefficients for the Inferior Parietal Lobule in Male Patients With Schizophrenia and Healthy Male Comparison Subjects

FIGURE 3. Gray Matter Volume Correlations Between the Inferior Parietal Lobule and Regions of the Prefrontal Cortex in 14 Male Schizophrenic Subjects^a

^a Solid lines indicate significance at p<0.01; dotted line indicates significance at p<0.05.

FIGURE 4. Gray Matter Volume Correlations Between the Inferior Parietal Lobule and Regions of the Temporal Lobe in 15 Male Schizophrenic Subjects^a

^a Solid lines indicate significance at p<0.01; dotted line indicates significance at p<0.05.

FIGURE 5. Midsagittal MRI Slice Depicting Measurement of Head Rotation (Tilt) About the Bitemporal Axis^a

^a The reference line (in red), used to measure head tilt, was drawn from the most anterior point of the corpus callosum to the most posterior point. This line was found to be virtually parallel to the bicommissural line (i.e., the white line drawn between the anterior commissure and the posterior commissure).

FIGURE 6. Regions of the Parietal Lobe^a

^a Image depicts a sagittal MRI slice approximately 5 mm lateral to the midsagittal slice, with the superior parietal gyrus traced in yellow and the postcentral gyrus in blue.

FIGURE 7. Three-Dimensional Surface Rendering of the Cortex^a

^a Gyri of the parietal lobe are color-coded as follows: postcentral gyrus (blue), superior parietal gyrus (green), supramarginal gyrus (red), and angular gyrus (yellow). See text and subsequent figures for detailed descriptions of the numerically designated boundaries and the alphabetically labeled planes.

FIGURE 8. Boundaries Defining Plane B (from figure 7) of the Cortex^a

^a The left side of the figure shows a midsagittal MRI slice with the reference line from figure 5 in red. The white line was drawn from the most anterior to the most posterior point of the corpus callosum, which formed a 9° angle with the reference line. The right side of the figure depicts the second line that defined the boundary of plane B, which was drawn on a lateral (sagittal) MRI slice with the same x, y coordinates as the red reference line.

FIGURE 9. Boundaries Defining Plane C (from figure 7) of the Cortex^a

^a The plane was defined by two parallel lines, the first of which is depicted in the midsagittal MRI slice on the left as a straight line drawn through the parieto-occipital fissure. The second line was drawn with identical x, y coordinates as the first line and is shown on the more lateral sagittal MRI slice on the right.