Figure 2.

Optical stimulation at 30 Hz results in increased exploration of familiar images. Paradigms used are shown above the bar graphs. Stimulation was paired with exploration of images (looking) in the choice period. Control conditions (CTL) are above the images and experimental conditions (EXP) are below the images. An empty box indicates no stimulation (NS). For CTL conditions, the laser was connected and operated exactly as in the EXP condition, but light was physically blocked from entering the fiber. Side was always counterbalanced, but for illustration purposes, choice images on the left and right represent familiar/novel (a, b) or familiar/familiar-paired images (c, d), respectively. Therefore, in all panels, the image and stimulation condition in which greater exploration was expected is shown on the right such that DR = (R − L)/(R + L). a, In CTL, as expected, rats (n = 7) preferentially explored the novel image. In EXP, when the familiar image was paired with 30 Hz optical stimulation, rats spent similar amounts of time exploring the paired familiar image and the novel image. The CTL DR was significantly higher than the EXP DR. b, Experiment in a was replicated with a second cohort of rats (n = 8). In CTL, again, rats explored the novel image more than the familiar one. In EXP, when looking at a familiar image was paired with 30 Hz stimulation, rats explored the familiar image more as if it were novel. c, In CTL, stimulation at 11 Hz does not decrease exploration of an already familiar stimulus. In EXP, stimulation at 30 Hz increased exploration of the paired familiar image (n = 6), showing that modulation of novelty exploratory behavior is frequency dependent. d, Replication of c except that NS is compared with 30 Hz (n = 8). Data are means ± normalized SEM. *p < 0.05; #p < 0.05 (t test), significant difference from zero.