Unit activity in somatosensory area II (SII) and tooth pulp stimulation in a cat

Within and near the rostral half of the anterior ectosylvian gyrus of an unanesthetized chronic cat, properties of units which responded to stimulation of the ipsilateral upper canine tooth pulp were studied. In total 75 responsive units were recorded by 192 microelectrode penetrations. Discharge patterns of these units to pulp stimulation were classified into 3 types: single spike response (4 units), short burst response (66 units) and prolonged response continuing up to several hundred msec (4 units). Spontaneous activities of one exceptional unit were depressed for 200-300 msec after pulp stimulation. These units were scattered in the explored cortical area, indicating that the SII somatotopically organized area may also receive nociceptive inputs. Most of these units responded to some modalities of mechanical stimuli applied to various parts of the body surface including face and head. This result suggests that they may correspond to the neurons unspecific with regard to modality and place observed in the anesthetized cat. Few units activated by pulp stimulation were encountered in the rostral portion of the anterior ectosylvian gyrus, where MELZACK and HAUGEN (1957) recorded the evoked potential by pulp stimulation. Five tooth pulp-sensitive units which were excited only by pin pricks and/or firm pressure were encountered on the dorsal bank of the anterior ectosylvian sulcus, the non-somatotopically organized area of SII.