Fig. 3.

VTA nondopamine neuron reciprocal input to cortex: extracellular recordings. A, Stimulation of the IC elicits a VTA non-DA spike (filled circle). B, A spontaneous spike that precedes IC stimulation extinguishes the driven spike. Calibration bar inA applies to B. Theasterisk signifies where the driven spike would have occurred had there been no collision. C, Stimulation of the IC also elicits orthodromic VTA non-DA spikes and produces a period of inhibition of an orthodromic spike that extends to 20 msec (C) when tested with equipotent paired stimuli at a 2× threshold stimulus level. D, IC stimulation produces a period of superexcitability for an antidromic spike when tested with equipotent paired stimuli at a 0.5× threshold stimulus level. Arrows indicate IC stimulus artifacts. The time between arrows or the interstimulus interval (ISI) in C andD is indicated in each graph.