[Neurophysiological studies in autism spectrum disorders--comparison with those in schizophrenia]

There have been reports that autism spectrum disorders (ASD) share common symptoms with schizophrenia. Several imaging studies showed the overlap of the impaired brain circuit in ASD and schizophrenia. Accordingly, differential diagnoses between adult ASD and schizophrenia without positive symptoms are sometimes difficult. We examined whether they show common results in functional MRI studies involving viewing photos of different facial expressions, such as angry, happy, sad, and neutral faces. We also examined oculomotor tasks that consist of saccadic and smooth pursuit eye movements in the two groups of patients. In fMRI studies, 15 schizophrenia patients (8 females) and 15 ASD patients (9 females) who met the criteria for DSM-IV participated. For the typically developed (TD) control group, 15 subjects (6 females) with no history of neurological or psychiatric disorders were recruited from the community. There was no significant difference in ages and sex ratios among these three groups. ANOVA comparison indicated that the ASD group showed significantly reduced activity in the right fusiform gyrus (FG) on viewing sad, happy, and neutral expressions but higher activity in the right mirror neuron system in the frontal cortex during viewing an angry expression. These results suggest a disturbance of the FG for face recognition and an excessive reaction to angry faces in ASD subjects. On the other hand, schizophrenics showed significantly reduced activation in widespread cortical areas, including the frontal, parietal, temporal, and occipital cortex, in comparison with TD and ASD individuals. We also examined voluntary control of saccadic and smooth pursuit eye movements in 13 adult subjects aged 20-35 with ASD (5 females) and compared the results with the performance of 13 TDs. Saccadic and smooth pursuit eye movements were recorded using an infrared system. Compared with TDs, 38% of the ASD subjects showed higher error rates in the anti-saccade task. However, in horizontal sinusoidal smooth pursuit, they showed normal gains. On the other hand, about 70% of 99 schizophrenics showed abnormalities in the antisaccade tasks. In the smooth pursuit task, 60-70% of schizophrenics showed a lower gain than controls. In this study, although all of the ASD subjects were adults and the number examined was relatively small, their abnormalities in fMRI and eye movement tasks were milder than those of schizophrenics.