Figure 2. Anticipatory shifts in spiking activity during AL.

(a) The left panel illustrates a screening session when the stimuli were presented in a randomized order. The right panel illustrates an AL session when the subject learned the order of the stimuli. The darker blue, pink and grey areas correspond to the presentations of the preceding, preferred and following stimuli. The lighter areas correspond to the ISIs. The dashed horizontal line is the average firing activity in the ISI window before the preceding stimulus. The solid black horizontal lines on the x axes represent time periods during which activity was significantly greater than the mean ISI response (that is, in the −500 to 0 ms window) before the preceding stimulus, continuously for at least 100 ms (paired t-test, P<0.05; see Methods). The spikes fired on individual trials are shown in the blue raster plots. This unit increased activity during the presentation of the preceding stimulus during AL, although this stimulus did not elicit a significant response during the screening session (left panel). (b) Another cell with increased activity during the ISI window between the preceding and preferred stimuli after learning. (c) Average activity of MTL neurons (N=42). Anticipatory activity before the preferred stimulus occurred during AL, but not during the screening sessions. Shaded area is the s.e.m. The dashed horizontal line at 0 is the baseline-corrected average ISI activity before the preceding stimulus. The solid black horizontal lines on the x axes represent time periods with activity significantly greater than in the ISI (−500 to 0 ms) before the preceding stimulus, for at least 300 ms. Note that the actual pictures used in the experiments are not shown here, as they were personal photographs from the patients. Eiffel Tower, Benh Lieu Song, CC BY-SA 2.0. Ian McKellen, Gage Skidmore, CC BY-SA 3.0.