Analysis of brain activity immediately before conscious teeth clenching using magnetoencephalographic method.

The reasons for unconscious teeth clenching have not been clarified. The long-term goal of our project was the elucidation of processing in the brain immediately before unconscious teeth clenching, in order to clarify its significance in humans. The objective of the present study was to establish a magnetoencephalographic (MEG) method of measuring brain activity immediately before clenching, and to clarify the time-course of brain activity immediately before conscious clenching. We measured the MEG signal in six subjects before, during and after clenching in a protocol that restricted head movement <5 mm. We derived tomographic estimates of brain activity for each time slice of data, as well as time courses for regional brain activations. Analysis of the tomographic images and time courses yielded statistical maps of activity in the motor, pre-motor and somatosensory cortices immediately before clenching in all subjects. Activations were found bilaterally, but with a strong unilateral bias in most subjects. Our results demonstrate that the MEG procedures, we have introduced are capable of measuring brain activity immediately before clenching, and indicate that analysis should begin from at least 200 ms before electromyogram onset.