Figure 5. De novo induction of an ‘on’ response in a pure ‘off’ simple cell recorded in a 27-week-old cat.

Conventions are as in Fig. 3. This neuron initially responded only to the extinction of the stimulus within its RF (C). Occasionally, one AP occurred during the ‘on’ period without a fixed latency. However, most of the presentations of the test stimulus failed to evoke any responses, as indicated by the LCR plot on the right. An ‘on’ response was imposed during the conditioning (P; 110 associations) by applying a positive current pulse (+3 nA), while the ‘off’ response was reduced when passing negative current (-3 nA). In spite of the fact that the current pulse started almost 1 s before the onset of the stimulus, its action was effective in triggering postsynaptic activity only during the ‘on’ period. After pairing, the cell fired in a consistent way during the presentation of the stimulus (119 APs for the ‘on’ period vs. 208 APs for the ‘off’ stimulation), although the response remained more transient and synchronized for the offset of the stimulus. The mean LCRs shifted from 0.094 to 0.207 following pairing (P < 0.005). This effect was still present 45 min after pairing (data not shown; P < 0.002). Calibration bars: 1 s; 10 AP s⁻¹.