Abstract
The fusiform gyrus is important for face and object recognition, is abnormal in schizophrenia, but has not been studied in schizotypal personality disorder (SPD). Thin-slice MR images showed no differences, either in right, left or total fusiform gyri volumes, between subjects with SPD (N=21) and normal controls (N=19). However, there was a correlation between severity of illusions and magical thinking suffered by the SPD subjects and smaller right fusiform gyrus volumes. This suggests that future studies may be useful in determining the functional competence of this gyrus in SPD.
. Introduction
The fusiform gyrus is likely important for face and object visual processing, as demonstrated by functional magnetic resonance imaging (fMRI) (Kanwisher et al., 1997). In addition, direct electrical stimulation of the gyrus can result in the formation of complex visual illusions (Lee et al., 2000). In schizophrenia, studies show that the fusiform gyrus evinces bilateral volume reductions in both a postmortem study (McDonald et al., 2000) and in an in vivo structural MRI study (Lee et al., 2002).
Schizotypal personality disorder (SPD) shares with schizophrenia: (1) a similar genetic diathesis (Kendler et al., 1993); (2) many biologic markers Siever et al., 2002 and Siever, 1994; (3) MRI in vivo volume reductions in left temporal lobe structures Dickey et al., 1999 and Downhill et al., 2001; and (4) impaired recognition of facial emotions (Mikhailova et al., 1996). By definition, persons with SPD can be functionally impaired by experiencing illusions. This study was undertaken to determine whether, like schizophrenics, SPD subjects also have smaller fusiform gyrus volumes than control subjects which might help to explain the experience of illusions.
. Results
3.1. Clinical measures
There was no difference between SPD and comparison subjects on age (mean SPD 37.1, NC 38.4; Students' t=−0.41, df=38, p=0.68), years of education (mean SPD 15.0, NC 15.4; Students' t=−1.001, df=38, p=0.32), premorbid IQ (Student's t=−1.28, df=29, p=0.15), and parental SES (mean SPD 3.4, NC 3.9; Students' t=−1.6, df=37, p=0.12), although there was a trend level difference in SES (mean SPD 3.35, NC 4.11; Students' t=−1.82, df=37, p=0.08).
3.2. Structural measures
There was no difference in whole brain volumes between the two groups (one-way ANOVA F=0.45, df=1, p=0.51). Repeated measures ANOVA revealed no main effect for fusiform side (F=0.016, df=1, p=0.9), nor diagnosis by side (F=0.036, df=1, p=0.85) with an effect size of 0.001 (very small) (Fig. 3). Nor was there a difference between groups in fusiform asymmetry (one-way ANOVA F=0.036, df=1, p=0.85) or total fusiform volume (one-way ANOVA F=0.007, df=1, p=0.93). The interrater reliability for the manual drawing of the fusiform for six cases by three raters was high (intraclass correlation r=0.9935 (right) and r=0.9988 (left)).
Scatterplot of SPD and comparison subjects' absolute right and left fusiform ...
Fig. 3.
Scatterplot of SPD and comparison subjects' absolute right and left fusiform volumes in ml with mean volumes indicated (note that this figure demonstrates absolute volumes not corrected for intracranial contents, but statistics were performed on corrected and normally distributed data).
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3.3. Clinical structural correlations
A negative correlation was found between the volume of the right fusiform gyrus and degree of impairment by self-report from illusions (Pearson r=−0.48, N=21, p<0.03) and magical thinking (Pearson r=−0.55, N=21, p=0.01).
