Figure 3.

Neurons selective for the upcoming response during the odor epoch in both dorsolateral (A) and dorsomedial (B) striatum show characteristics consistent with S–R encoding. Histograms show the free-choice/forced-choice index (average peak-normalized firing rate on free-choice trials minus that on matched forced-choice trials across all blocks) for all neurons that are selective for the upcoming response during the odor epoch (beginning 50 ms after presentation of the odor, ending at odor port exit). Those plotted in black are significantly selective for either forced-choice trials (negative values) or free-choice trials (positive values). Significance was tested using a paired t-test (p < 0.05) comparing free-choice trials with forced-choice trials matched for response, outcome, and position within the block. Asterisks in the histograms show the selectivity indices of the example neurons shown in Figures 2B,D. Curves on the right show average peak-normalized firing rates (±SEM), relative to baseline, aligned on the beginning of odor, for the free-choice selective population for dorsolateral striatum and the forced-choice selective population for dorsomedial striatum. Very few neurons in dorsolateral striatum were forced-choice preferring and very few in dorsomedial striatum were free-choice preferring. Curves were collapsed across each neuron's preferred direction (designated according to the direction and block with the highest average firing rate). Dorsomedial striatum included a significantly greater percentage of selective neurons, which were more likely to prefer forced-choice trials.