Figure 4.

Dopamine-like responses evoked by cue develop similarly with learning, while adults have larger reward delivery evoked responses than adolescents. Cue-evoked population responses increased with learning, and the progression of this response did not differ by age group. However, adolescents demonstrated a reduced reward-evoked response compared to adults. In addition, adults, but not adolescents, showed a sustained elevation in activity beginning 1 second prior to reward delivery. Peri-reward neuronal activity grew stronger in magnitude across sessions. Each panel depicts the normalized and smoothed neuronal responses of dopamine-like neurons in both age groups, averaged across trials and neurons. Data are aligned to the onset time of the cue (left column), time of the instrumental action (middle column), and the time of reward delivery. Data are depicted for the first 6 sessions (one session per row) prior to extinction as mean ± SE. The cumulative number of dopamine-like units recorded in each session is depicted in the upper left corner of the left column of each row. The topmost number indicates adolescent units. Tan overlay indicates maintenance sessions.