Fig. 5.

Prestimulus increases in firing rate were aligned to the subsequent stimulus-guided nose poke. A and B: the latency to make a stimulus-guided nose poke differed between trial types. During correct trials (orange, A), rats responded with a mean latency of 0.441 s after stimulus onset, whereas latency occurred 1.100 s after stimulus onset during incorrect trials (green, B). C: mean normalized firing rate of prestimulus responsive neurons aligned to stimulus-guided nose poke onset (at t = 0 s, vertical black line). The shading indicates SE. The orange and green vertical dotted lines mark the average time of stimulus onset preceding the nose poke for correct trials (orange) and incorrect trials (green). Units increased firing rate before stimulus onset and continued to fire at an elevated rate until nose poke onset. The change in firing rate was greater during correct trials (orange line). D: prestimulus responsive neurons did not respond to nose poking events that were not stimulus-guided (i.e., premature nose pokes during the prestimulus period). These data suggest that VTA neurons respond during stimulus expectancy and continue until the stimulus-guided action, but do not respond to actions alone.