Multiple observations on a single unrestrained cat of long-lasting facilitation of transmission through the lateral geniculate nucleus.

The field potential responses of the lateral geniculate nucleus (LGN) to test electrical stimuli delivered to the optic tract (OT) were recorded in an unanaesthetised, freely moving cat. The response consisted of two waves, one attributable to depolarisation of the OT terminals (t), and one attributable to the postsynaptic response (r) of LGN neurones. A train of 300 electrical stimuli at 0.2 Hz to the OT alone did not influence the amplitude of these waveforms. In contrast after a train of 150 pulses had been delivered to both the OT (at 0.2 Hz) and LGN (pseudo-random with mean intervals of 0.2 Hz), the amplitude of both the t and r waves to test OT electrical stimuli was markedly enhanced for the following 6 days. Enhancement of the t wave followed that of the r wave.