Cortical responses evoked by tooth pulp stimulation in the cat. Surface and intracortical responses.

In lightly chloralose-anaesthetized cats selective stimulation of tooth pulp afferents elicited responses in coronal, anterior suprasylvian and adjacent cortical gyri. In the lateral part of coronal gyrus the potentials evoked from the contralateral canine tooth pulps were initially positive. Such responses from the upper and lower teeth had different cortical distribution suggesting a topographical organization. In the regions adjacent to those with initially positive responses stimulation of the same tooth pulp evoked initially negative potentials. Stimulation of ipsilateral tooth pulp afferents elicited almost exclusively initially negative potentials with a similar distribution as the responses of contralateral teeth but with longer latency. Laminar analysis showed that the region with initial positivity in the response to stimulation of the tooth pulp coincided with an intracortical negative focal potential of maximum amplitude mainly in lamina IV. In areas with initially negative responses the maximum of the focal potential following tooth pulp stimulation was obtained in superficial cortical layers. It is postulated that the projection system underlying the initially positive cortical responses has a topographically arranged cortical projection terminating mainly in lamina IV. The projection system eliciting the initially negative potentials, has a widespread cortical distribution and produces excitation predominantly in the superficial laminae.