Postsynaptic potential patterns evoked upon cells in sensorimotor cortex of cat by stimulation at the periphery

Abstract

Intracellular and extracellular recordings were obtained from neurons in the sensorimotor forepaw cortex of chloralose-anesthetized, domestic cats. Cells responding with either spike or slow potential activity only after stimulation of the contralateral forepaw were classified as s neurons; those responding additionally after stimulation of other extremities were classed as m neurons. The postsynaptic potential changes evoked by single electric shock to the central footpad of each limb were of particular interest. Seven of the eight well-isolated s neurons responded to contralateral forepaw shock with a long duration depolarization; one responded with a short duration EPSP, followed immediately by a Cl −-dependent hyperpolarization. No intracellular membrane potential changes were seen on the s neurons after stimulation of other limbs. The typical response of m neurons to stimulation of any limb was a long-duration EPSP, followed by a long, weak IPSP. The IPSP was most prominent after contralateral forepaw shock, occasionally being indistinct after stimulation of other limbs. Although the inhibition typically follows an EPSP, 5 of 83 neurons responded to contralateral forepaw shock with an initial hyperpolarization. The observations are used to evaluate four possible mechanisms for the production of cortical inhibition. The data are best interpreted as resulting from a direct, thalamocortical inhibitory projection; the data are inconsistent with an intracortical, “recurrent” model.