Spontaneous electrical activity of a trigeminal mesencephalic neuron responsive only to spontaneous movement of the macrovibrissae bundle. (A) Spontaneous electrical activity of a trigeminal mesencephalic neuron under baseline conditions (i.e., with the vibrissae in resting position). (B) The same activity during fan-like movement of the macrovibrissae bundle and (C) during simultaneous stretching of the masseter muscle. The neuron did not respond to the masseter stretch, which only induced evoked field potentials in the nucleus. Arrows indicate the beginning ("on") and the end ("off") of the muscle stretching. Calibrations: horizontal 0.5 s; vertical 250 μV.