Figure 2.

Cortical firing patterns and the conditioning procedure. A, Activity for a 2 sec period at electrodes 1-100 is shown during the conditioning procedure for experiment R20. Spikes at the trigger channel (n.76), at electrodes 53 and 64 (columns E₃ and E₂, respectively) and at electrodes 35 and 46 (columns C₃ and C₂, respectively), are shown as gray dots in black boxes. B, Conditioning stimuli are shown for the same 2 sec period of activity. In the top trace, spike times at electrode 76 are shown as vertical gray bars. Immediately below, times of the E₂-E₃ stimulus are shown as vertical bars. Each event at electrode 76 triggered an E₂-E₃ whisker stimulus with a 1 msec delay. Further below, times of the C₂-C₃ stimulus are shown; note the identical temporal structure as the E₂-E₃ stimulus, but with a 300 msec delay. The bottom four traces show spike trains recorded in the burst-conditioned cortical columns (E₂-E₃; black) and the interburst-conditioned cortical columns (C₂-C₃; gray). Spike trains in the burst-conditioned cortical columns were temporally correlated with the stimuli, whereas spike trains in the interburst-conditioned cortical columns were more dispersed in time. C, Relative timing between stimuli at the burst-conditioned and interburst-conditioned whisker pairs summated across all five experiments. Gray histogram bars show the probability that an interburst stimulus will follow a burst stimulus with a given delay, where as the black histogram bars show the probability that a burst stimulus will follow an interburst stimulus with a given delay. The histogram value of 1 is determined by the conditioning protocol where by interburst stimuli always followed burst-triggered stimuli after a 300 m sec delay. The other values of the histogram are an outcome of the complex firing patterns at the trigger electrode. Note that at delays of <∼100 msec, when stimulus interactions might be pronounced, the probabilities were approximately equivalent.