100 ms (selected with replacement from uniform distribution), the light opposite the location of the first cue was turned on and remained on until a behavioral response was made. These trials were referred to as STOP-change trials and were randomly interleaved with GO trials (i.e., the other 80% of trials) (Fig. 1 A and B). On STOP-change trials, rats were required to stop their initial movement signaled by the first cue and to respond in the direction of the second light in order to receive reward. Upon correct responding, rats were required to remain in the fluid well for a variable time period between 800 and 1,000 ms (prefluid delay) before a reward was delivered (10% sucrose solution). Intertrial intervals (ITI) for correct and incorrect responses was held at 4 and 7 s, respectively. Error trials (i.e., response in the incorrect direction) were immediately followed by the extinguishing of the house lights and ITI onset.
