Characteristics of periodontal mechanosensitive neurons in the first somatosensory cortex of the cat.

Response properties of periodontal mechanosensitive (PM) units which were activated by the mechanical stimulation of canine teeth were studied in the oral area of somatosensory cortex S I (anterior coronal gyrus) of the cat. Spike discharges of PM units were recorded as post-stimulus time histograms (PSTHs). Most PM units showed more or less spontaneous activity and phasic response properties to the trapezoid waveform stimulation. When the rate of stimulus application was increased, the initial peak value of the PSTH increased and its crest time decreased. Direction-selective PM units which changed their response discharge rates according to the direction of the stimuli applied to the canine teeth were found in this cortical area. Posterior-directed mechanical stimulation was more effective for eliciting the spike discharges of PM units than anterior-directed stimulation. Applying the test and conditioning stimuli to the contralateral or ipsilateral canine teeth, interactions of afferent inputs received by the mechanoreceptors of the periodontal tissues of different teeth were studied. Test responses of PM units were inhibited for 20-50 ms after the onset of the conditioning stimuli.