Figure 2. Comparison of response patterns from individual rats performing operant behaviors to obtain electrical stimulation of the septum or optogenetic stimulation of dopamine neurons.

(A) Cumulative bar press responses from a high-performing rat implanted with a stimulating electrode in the septum. Each bar press was reinforced with current delivered to the tip of the implanted electrode; background color indicates the voltage of current applied. The rate of responding increased with voltage, and ceased when current was not applied. Note that behavioral data from multiple daily sessions were collapsed to produce the figure depicted. Adapted with permission from Olds and Milner (1954). (B) Cumulative nosepoke responses from a high-performing rat receiving optogenetic stimulation of ventral tegmental area dopamine neurons. Each nosepoke was reinforced with 1 second of 20 Hz optical stimulation. The color of the line indicates behavior across 4 consecutive daily sessions. (C) Response rate from the same animal shown in B during a behavioral session where the length of optical stimulation delivered with each response was systematically varied. Each stimulation length was tested multiple times; error bars represent SEM. Response rate increased with stimulation length. (D) Cumulative responses for the same animal during a within-session extinction test. Responding ceased when no longer reinforced, and resumed when the laser was turn back on. Stimulation length was 1 sec as in B. Panels b-d were adapted with permission from Witten et al. (2011). Note the close correspondence of the pattern of responding in A with the patterns observed in B-D.