Fig. 1.

Hippocampal neural activity and performance of the delayed-non-match-to-sample (DNMS) task. a Ensemble firing patterns on single DNMS trials recorded from electrode arrays (illustrated at top) were analyzed by multivariate CDA. The discriminant function (DF5) that contributed to the sample response (S_mR) yielded differential firing for correct and error trials plotted as perievent histograms (±1.5 s), represented here as color contours of firing rates across all neurons recorded in a single animal. Each of the four contour plots represents the firing pattern of the same ensemble on a different individual DNMS trial. Patterns in the left column illustrate “strong” encoding of right and left S_mRs respectively, while patterns in the right column reflect “weak” encoding of S_mRs resulting in behavioral errors. Individual neurons are listed (1–16) on vertical axis and time on the horizontal axis with “0.0 s” demarcating the occurrence of the S_mR. The color scale depicts firing rate for contour plots: blue ≤1 Hz to red ≥10 Hz. b DNMS behavioral performance curves depicting mean (±SEM) percent correct responses on trials with delays of 1–80 s. Animals were trained with delays of 1–30 s and probe trials with delays of 40, 50, 60, or 80 s interspersed randomly to test strength of encoding. Mean correct performance in vehicle sessions (solid line), rimonabant sessions (dashed line and filled circles). Plot of weak code (DF5s < 0.90: performance) trials in vehicle sessions (dashed line and unfilled circles). *F_(1,2514)>7.39, p<0.01; **F_(1,2514)>13.69, p<0.001. c Frequency distribution of S_mR code strengths (DF5 scores) for 40–80 s trials shown in B computed for all animals (n=13) across five to ten sessions ≥ 100 trials. Mean (±SEM) frequency (% of total trials) of occurrence of each of code strength (DF5 score bin=0.1, range 0–3.0) classified as weak (DF5=0–1.0, red), normal (1.0–2.0, blue), and strong (2.0–3.0, green) for vehicle (left) and rimonabant (right) sessions