Figure 1. Rats formed two associative memories that differed in incidental, physical features.

(A) Rats were implanted with two eyelid wires to deliver mild electrical current (US) and record anticipatory blinking activity (CRs). Single neural activity was collected from the prelimbic region of the mPFC from the first day of conditioning. Conditioning took place in two chambers, in which either a tone (ACS) or light (VCS) was presented alone (CS alone, 20 trials) or preceding the US by 500 ms (CS-US, 80 trials). (B) Averaged EMG amplitude during Early (left) and Late learning (right) during CS-alone trials (top) and CS-US paired trials (bottom). (C) CR expression (CR%; ±SEM) increased over days for both ACS-US (red) and VCS-US (blue) conditions, but not during the respective CS-alone conditions (magenta, turquoise). (D) Within sessions in which rats reached asymptotic responding, CR% showed an abrupt transition upon the shift from the block of CS-alone trials (magenta; turquoise) to the block of CS-US paired trials (red; blue).

DOI: http://dx.doi.org/10.7554/eLife.22177.003

Figure 1—figure supplement 1. Behavioral performance in two blocks of trace eyeblink conditioning.

(A) In all four rats, trials with a conditioned response (CR%) gradually increased during two conditions with CS-US pairings (ACS-US paired, red; VCS-US paired, blue), but not during two conditions with the CS alone presentation (ACS alone, magenta; VCS alone, turquois). Based on CR% and days since asymptotic responding, sessions were divided into five successive stages (vertical lines). (B) In a few trials, EMG amplitude during a period before CS onset significantly changed from baseline. The proportion of these trials (mean ± SEM, n = 4 rats) did not increase across sessions or differ across four conditions. See (A) for the definition of line color. (C) In some trials, the rats engaged in an activity that greatly increased EMG amplitude before CS onset. (D) The frequency of these ‘hyperactive’ trials did not change across sessions or differ between four conditions (mean ± SEM, n = 4 rats). See (A) for the definition of line color.

DOI: http://dx.doi.org/10.7554/eLife.22177.004