Figure 2.

Ventral striatal units showing firing patterns associated with one or more reward sites. Rats ran along a triangular track to obtain three types of reward (S, sucrose; V, vanilla; C, chocolate). Top panels, Spatial distribution of firing rates of two individual neurons. A, B, Local firing rates ranged from 0 to maxima of 19 Hz (A) and 18 Hz (B). Bottom panels, Perievent time histograms for both cells synchronized on reward site arrivals. Rows represent different reward types, whereas columns differentiate between the presence and absence of reward. Firing rate is in bins of 250 ms. The red ticks indicate arrivals at other reward sites. A, Neuron showing an increased firing rate shortly before and after arriving at the sucrose reward site, mainly when a reward was obtained. B, Neuron increased its firing rate before arrival at two sites differentially for the rewarded versus nonrewarded condition. The response at the vanilla site was stronger than at the chocolate site. The rat may have detected the availability of reward before arriving at the well by visual or olfactory cues, although reward cups were filled outside the rat's field of view.