Effects of experimentally deviated mandibular position on stress response.

The purpose of this study was to investigate the effects of stress on -prefrontal cortex (PFC), emotion (using visual analogue scale, VAS, and State-Trait Anxiety Inventory, STAI), and the autonomic nervous system (ANS). Two types of stress were applied: (1) malocclusion-induced physical stress and (2) mental stress induced by an arithmetic task. Malocclusion was induced using an experimentally deviated mandibular device (EDMD) to obtain an experimentally deviated mandibular position (EDMP). A total of 11 healthy volunteers participated in the study. On day 1 they performed a pretrial arithmetic task followed by a 10-min rest, after which they performed a posttrial EDMD + arithmetic task or rest device + arithmetic task. These two tasks were selected at random and assigned at the rate of one per day. Activity in the PFC tended to show an increase in the pretrial arithmetic tasks and rest device + arithmetic task, but a decrease in the EDMD + arithmetic task compared with the rest device + arithmetic task. Heart rate significantly increased during the rest device + arithmetic task, whereas no significant difference was observed during the EDMD + arithmetic task. The EDMD + arithmetic task significantly increased STAI scores (p = 0.0047), and the significant decrease in VAS indicated "unpleasant" (p = 0.035). These findings suggest that EDMP-induced reduction in the level of PFC activity was a response to discomfort, indicating that EDMP affects systemic function such as that of the ANS as an unpleasant stressor.

Effects of occlusal disharmony on working memory performance and prefrontal cortex activity induced by working memory tasks measured by NIRS.

The effects of artificial occlusal disharmony (AOD) on working memory function and prefrontal cortex (PFC) activity in the elderly were examined. We evaluated working memory function using the modified Sternberg test (ST). We measured activity in the bilateral PFC during ST using near-infrared spectroscopy (NIRS) before and after AOD: the mandibular position was displaced by a splint for 10 min. AOD caused a gradual increase of oxyhemoglobin (oxy-Hb) in the bilateral PFC. The response time of ST (six digits) after AOD was longer than that before AOD. The oxy-Hb increase during ST after AOD was smaller than that before AOD. These results indicate that short-term physical stress caused by AOD decreased working memory function in elderly subjects, associated with a decrease of the evoked PFC activity during working memory function.