Long-term potentiation in the cat somatosensory cortex.

Intracellular, in-vivo recordings were used to identify neurons in the cat somatosensory cortex in which long-term potentiation (LTP) was induced. Amplitudes of EPSPs produced by microstimulation in the motor cortex (area 4 gamma) were recorded before and after tetanic stimulation (200 Hz, 20 s). In 8/13 cells (62%), EPSP amplitudes increased significantly following the tetanic stimulation. LTP was induced exclusively in cells which produced monosynaptic EPSPs. Six of these cells were labeled by intracellular injections of biocytin. All the cells in which LTP was induced were pyramidal neurons, and were located exclusively in layers II or III of the somatosensory cortex; cells in deeper cortical layers were not potentiated. These data substantiate our previous findings demonstrating LTP in corticocortical pathways and suggest that these pathways play an important role in cortical synaptic plasticity.