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.