The influence of eye closure on muscle activity in the anterior temporal region

In the experiments reported here the influence of eye closure upon the muscle tone in the region of the anterior temporal muscles was studied during mandibular rest in four patients with TMJ dysfunction and in four healthy subjects. The muscle activity as well as the cortical activity (EEG) of the patients was influenced by changes in visual stimulation. EMG (the anterior temporal region) and EEG (parieto-occipital region) were recorded with needle electrodes. Ongoing EMG activity was present in all patients when their eyes were open. Closure of both eyes reduced the muscle activity by 50-100%. Closure of one eye could also abolish all activity but the degree of this influence was variable. Opening of the eyes blocked the alpha rhythm in the EEG. Simultaneously, increased activity was observed in the region of the temporal muscle. The activity level in the temporal region of the healthy subjects was very low and could easily be reduced to noise level using ordinary relaxation manoeuvres without eye closure. The results reported here indicate that visual stimulation may increase muscle tone in the temporal region probably as part of an arousal reaction. It is, however, possible that the activity might stem not from the temporalis muscle but from the temporoparietalis.