Changes in electroencephalographic activities following pressure stimulation in humans.

We investigated brain activity in response to orofacial pain in 20 healthy subjects in order to characterize the relationship between pain and changes in brain function. First, the pressure pain threshold (PPT) at the styloid process of the temporal bone (Libman's point) of 20 subjects was measured by a pressure algometer. Second, electroencephalographic (EEG) changes of 20 subjects before and after 10 s of constant pressure stimulation at Libman's point were measured. These 20 subjects were divided into two groups: 10 subjects with higher PPT (high group) and 10 subjects with lower PPT (low group). EEG change in beta activity after stimulation was greater in the low group than the high group, and there was a significant negative correlation between this change and PPT, with even minor constant stimulation inducing larger EEG change in individuals highly receptive to pain. The present study demonstrated that a relative reduction in beta activity after pain stimulation was more remarkable in subjects with lower PPT than in subjects with higher PPT, and that this change was closely related to a hemispheric balance, with even minor constant stimulation inducing changes in brain waves in individuals highly sensitive to pain.