Functional magnetic resonance imaging (fMRT) has become an important tool to study non-invasively and continuously activation of the human brain, because bold oxygen level dependent (BOLD) contrast can be measured in vivo. Recently, the ncoral bases of mental imagery have been both a topic of intense debate and a domain of extensive investigations using fMRT. We examined the effect of imaginary mastication on activation of the sensorimotor cortex of the human brain using fRMT. Measurements were performed on a conventional whole body 1.5T clinical scanner using a single shot, multislice echo-planar imaging sequence

(TR/TE/FA/FOV/MA=300ms/50ms/90degrees/240mm/96x96,
thickness=7mm, number of slices=4).

Three normal volunteers underwent fRMT during 15 biting tasks, tapping or 30% maximal voluntary contraction (MVC), and same 15 imagination tasks of tapping or 30% MVC with concomitant monitoring of surface electromyographic signals from the bilateral masseter muscles. The findings showed that the signal intensity in the sensorimotor cortex was significantly increased by not only actual biting tasks but also imagination tasks, with the effect of actual biting tasks being about 4-fold higher than that of imagination tasks (p<0.0001, paired, two-tailed t-test).

These findings suggest that activation of the sensorimotor cortex in mastication increases with not only the biting force but also imaginary mastication.

This study was supported in part by a grant (No. 09557154) from the Scientific Research Fund of the Japanese Ministry of Education.