Figure 10. Effects of a fixed delay protocol in a complex cell recorded in a 6-week-old kitten.

Conventions are as in Fig. 3. PSTHs are shown in the left column for the paired position, and in the right column for the unpaired position. Before pairing, a tonic ‘on’ response and a more transient ‘off’ response were observed uniformly across the RF. The pairing procedure (P, data not shown) consisted of 50 associations of a negative current (-3 nA, 2120 ms duration) with the onset of the light bar and a positive current (+3.2 nA, 2150 ms) following the offset of the same stimulus with a constant delay of 500 ms. A progressive change developed over 40 min after pairing, resulting in a significant depression of the ‘on’ response (P < 0.0005), whereas a late ‘off’ response appeared de novo in the paired position. The latency of the new response precisely matched the onset delay of the iontophoretic pulse used during pairing. The ‘on-off’ ratio was unchanged in the unpaired position. The modification in the paired position was still present more than 1 h after the end of the pairing procedure, at which time the neuron was lost. Calibration bars: 1 s; 20 AP s⁻¹.