Activity in cortical cells after stimulation of tooth pulp afferents in the cat. Intracellular analysis.

The projection of tooth pulp afferents to cortical cells was studied in intracellular recordings. In a small region of the coronal gyrus, cells in lamina IV were responding at stimulation of contralateral tooth pulp afferents with short latency, steeply rising EPSPs, and one or two action potentials followed by an IPSP. These cells received convergence from skin afferents. In a large cortical area in the coronal, anterior suprasylvian and anterior ectosylvian gyri, tooth pulp stimulation elicited long latency, long lasting EPSPs not succeeded by hyperpolarization mainly in superficial cortical cells. These EPSPs could elicit trains of spikes. A complex type of responses consisted of a short latency EPSP with one or two spikes followed by hyperpolarization which in part was counteracted by a second, long latency EPSP of long duration. Stimulation of low threshold contralateral skin afferents usually gave short latency EPSPs with spikes followed by long lasting hyperpolarization. A common feature of many cells was a high convergence from tooth pulp afferents and bilateral low threshold skin afferents. The response characteristics at tooth pulp stimulation compared to low threshold input are discussed in relation to cortical mechanisms of pain.