Potentiation of neuronal responses to natural visual input paired with postsynaptic activation in the hippocampus of the awake monkey.

Extracellular recordings were made in the hippocampal formation while the monkey performed a simple visual discrimination task in which the stimuli consisted of coloured patterns presented serially. By using this natural visual input to single hippocampal neurones, and experimentally pairing one of the stimuli with postsynaptic excitation induced by iontophoretically applied L-glutamate, we demonstrate that selective synaptic potentiation can result. Seven of 29 neurones tested showed potentiation. The potentiation was selective in that enhanced responses only occurred to the previously paired stimulus, and not to other visual stimuli. The potentiation was observed in CA3 neurones and lasted approximately 15 min. In each case the latency of the potentiated response occurred at 160 ms following the onset time of the stimulus.