Fig. 2.

Histograms and raster plots of exemplar CA1 single neurons recorded on CS-alone retention trials that showed encoding of trace interval duration. Each histogram shows the sum of action potentials in 500 msec bins across the initial 7–10 CS-alone retention trials after trace conditioning with a 10 sec trace interval (left) or a 20 sec trace interval (right). These neurons showed increases in firing on CS-alone trials ∼10 or 20 sec after CS offset for each of these groups, respectively. The rasters above each histogram plot the occurrence of each action potential (dots) on each of the first 10 CS-alone retention trials. The plots show that the timed responses for these example neurons were fairly consistent across the first 5 or 10 CS-alone retention trials. No USs were presented on any of the trials in this figure. The arrows mark the latency of the US onset used on previous trace fear conditioning trials. The number of trials used for each histogram is shown at thetop left of each panel. Although only a subset of all neurons recorded from each animal showed trace encoding, each of the example neurons in this figure was selected from a different rabbit, to demonstrate that this encoding effect was consistent across animals.