THE EFFECTS OF LOCALIZED INACTIVATION OF SOMATOSENSORY CORTEX, AREA-2, ON THE CAT MOTOR CORTEX

Direct corticocortical afferents to the primary motor cortex (MI) orig inate in area 2 and area 3a of the primary somatosensory cortex (SI). The functional and morphological characteristics of the two pathways i ndicate that they relay different sensory signals to MI. The role of a rea 2 in relaying peripheral information to the cat MI was studied usi ng electrophysiological techniques. Neurons that responded to stimulat ion of peripheral receptive fields on the contralateral forepaw were i dentified in MI by extracellular recordings. In area 2 of SI, neurons with the same receptive field modality and location as those in MI wer e also identified. Field potentials to electrical stimulation of the p eripheral receptive field were recorded at the somatotopically matched sites in both MI and SI. Neuronal activity at the recording site in a rea 2 was blocked by injection of lidocaine, a local anesthetic. Chang es in MI and area 2 responses were monitored before and after inactiva tion of area 2. Neuronal activity near the injection site was abolishe d, and evoked potentials (EPs) in area 2 were considerably diminished immediately following the injection. In MI, spontaneous activity level s were altered at some sites, but overall these changes were not signi ficant. MI EPs recorded in response to peripheral stimulation were alt ered, and various patterns of change were noted in the early and late phases of the EPs. Changes often occurred in only one phase of the res ponse. In some EPs, both early and late phases changed, but the direct ion and magnitude of change in one phase were not always linked to suc h changes in the other phase. Both increases and decreases in the ampl itude and the area of each phase were observed. The morphological char acteristics of the projection were reviewed and related to the finding s in the study. It is proposed that inherent features of the pathway m ay account for the variable patterns of change that were observed.