Search

The mu rhythm is regarded as a physiological indicator of the human mirror neuron system (MNS). The dysfunctional MNS hypothesis in patients with autistic spectrum disorder (ASD) has often been tested using EEG and MEG, targeting mu rhythm suppression during action observation/execution, although with controversial results. We explored neural activity related to the MNS in patients with ASD, focusing on power increase in the beta frequency band after observation and execution of movements, known as post-movement beta rebound (PMBR). Multiple source beamformer (MSBF) and BrainVoyager QX were used for MEG source imaging and statistical group analysis, respectively. Seven patients with ASD and ten normal subjects participated in this study. During the MEG recordings, the subjects were asked to observe and later execute object-related hand actions performed by an experimenter. We found that both groups exhibited pronounced PMBR exceeding 20% when observing and executing actions with a similar topographic distribution of maximal activity. However, significantly reduced PMBR was found only during the observation condition in the patients relative to controls in cortical regions within the MNS, namely the sensorimotor area, premotor cortex and superior temporal gyrus. Reduced PMBR during the observation condition was also found in the medial prefrontal cortex. These results support the notion of a dysfunctional execution/observation matching system related to MNS impairment in patients with ASD, and the feasibility of using MEG to detect neural activity, in particular PMBR abnormalities, as an index of MNS dysfunction during performance of motor or cognitive tasks.

Backgrounds: The digit symbol substitution test (DSST) is a clinically useful and widely accepted tool for the detection of various psychiatric disorders. Investigating neural activity during the DSST is useful when considering the relationship between the poor performance on the DSST and neurocognitive deficits. However, obtaining reliable functional imaging of the neural mechanisms associated with this test is challenging due to motion artifacts. Aims: To circumvent this problem, we examined frontal lobe activity during the DSST using multichannel near-infrared spectroscopy, a noninvasive functional imaging technique that does not interfere with the DSST procedure. Methods: Twenty-five healthy volunteers were enrolled in this study. Changes in the concentration of oxygenated hemoglobin (oxyHb) during the DSST were determined bilaterally in 52 measurement points (channels) on the frontal area. Results: We found significant increases in oxyHb in more than 70% of the channels, with the intensity of the increase being more pronounced in the left hemisphere. Several channels showed significant positive correlations between changes in oxyHb and DSST performance. Some of the channels with a significant increase in oxyHb during the DSST did not show a correlation with the DSST performance. Conclusions: Our findings indicate that the DSST could prove useful as a frontal lobe stimulating task. Further examinations of DSST/near-infrared spectroscopy analyses of neural mechanisms in patients with psychiatric and neurological diseases are necessary to assess its effectiveness in clinical practice for the evaluation of neuropsychopathology.

Working memory performance has been inconsistently reported in autism spectrum disorders (ASD). Several studies in ASD have found normal performance in digit span and poor performance in digit symbol task although these are closely related with working memory. It is assumed that poor performance in digit symbol could be explained by confirmatory behavior, which is induced due to the vague memory representation of number-symbol association. Therefore it was hypothesized that the performance of working memory task, in which vagueness did not cause confirmatory behavior, would be normal in ASD. For this purpose, the Advanced Trail Making Test (ATMT) was used. The performance of digit span, digit symbol and ATMT was compared between ASD and normal control. The digit span, digit symbol and ATMT was given to 16 ASD subjects and 28 IQ-, age- and sex-matched control subjects. The scores of these tasks were compared. A significantly lower score for ASD was found only in digit symbol compared with control subjects. There were no significant difference in digit span and working memory estimated by ATMT. Discrepancy of scores among working memory-related tasks was demonstrated in ASD. Poor digit symbol performance, normal digit span and normal working memory in ATMT implied that ASD subjects would be intact in working memory itself, and that superficial working memory dysfunction might be observed due to confirmatory behavior in digit symbol. Therefore, to evaluate working memory in ASD, tasks that could stimulate psychopathology specific to ASD should be avoided.

Eating disorders are common psychiatric disorders in young women. The aim of the present study was to evaluate the gastric electrical activity of patients with eating disorders and its relation to their symptoms. The electrogastrography (EGG) was performed before and after a water load test for outpatients with eating disorders (n = 36; 14 anorexia nervosa, 14 bulimia nervosa, eight eating disorder not otherwise specified) and healthy women (n = 19). A structured interview (Eating Disorder Examination) was used to assess clinical symptoms. The percentage of normal gastric myoelectrical power was significantly smaller in the eating disorder patients (44.5% vs 74.2%; P < 0.05), while the percentage of bradygastric power was significantly greater, both before and after the water load test compared with the control subjects (30.4% vs 10.4%; P < 0.05). In addition, moderate correlation was found between the duration of illness and the percentage of bradygastria (P < 0.05). In conclusion, it is suggested that longstanding abnormal eating in patients with eating disorders may induce disturbances to gastric motor function, resulting in their abnormal, eating-related behavior, and form a symptomatic vicious circle. The EGG may be a promising method for determining the pathophysiology of eating disorders and for developing effective therapeutic approaches.