IDENTIFICATION OF NEURONS PRODUCING LONG-TERM POTENTIATION IN THE CAT MOTOR CORTEX - INTRACELLULAR-RECORDINGS AND LABELING

Intracellular, in vivo recordings were used to identify and subsequently to label neurons in the cat motor cortex in which long‐term potentiation (LTP) was induced. Thirty‐nine motor cortical neurons that produced excitatory postsynaptic potentials (EPSPs) in response to microstimulation in areas 1‐‐2 (SI) or in area 5a (SIII) were studied. Amplitudes of EPSPs produced in response to test stimulation (1 Hz) were recorded before and after tetanic stimulation (200 Hz, 20 seconds). In 25/39 cells (64%), EPSP amplitudes were significantly increased following the tetanic stimulation (65 ± 51% average increase), and remained at the potentiated level as long as stable recordings could be maintained (20 ± 18 minutes, maximum = 90 minutes). LTP was induced exclusively in cells that produced monosynpatic EPSPs in response to area 1‐‐2 or area 5a stimulation. Of the 39 analyzed cells, 13 were labeled by intracellular injections of 5% biocytin. Neurons in which LTP was induced included both pyramidal and nonpyramidal cells and were located exclusively in layers II or III of the motor cortex; cells in deeper cortical layers were not potentiated. These findings indicate that various corticocortical inputs can increase the efficacy of synaptic transmission in a subset of motor cortical neurons. We propose that this plasticity in synaptic transmission constitutes one of the bases of motor learning and memory. Copyright © 1990 Wiley‐Liss, Inc.