Fig. 3.

Influence of delaying the delivery of reward in the instrumental task condition in one tonically active neuron. Eachdot in the raster displays represents one neuronal impulse, and each line of dots represents the neuronal activity occurring during a single trial. Dot displays and perievent time histograms are aligned on the onset of the trigger stimulus or the delivery of reward, which are marked by vertical lines. The sequence of trials is shown chronologically fromtop to bottom in each raster display. The change of condition occurred over three successive blocks of trials. This neuron showed a weak response to reward in the immediate condition but had a clear-cut response to the same event in both the fixed delay and variable delay conditions. This neuron also showed a response to the trigger stimulus that persisted in all instances. Vertical calibration on histograms is in impulses per bin. Bin width for histograms is 10 msec.