Fig. 4. NAcc responses to VTA stimulation (VTA Stim.) with trains of pulses (arrowheads).a, Overlay of responses from a neonatally lesioned rat (top) and a sham rat (bottom) recorded after P56 (PD56). In the neonatally lesioned animal, high-frequency spike firing could be detected during the membrane potential depolarization. This was not observed in the sham rat. b, Responses in a neonatally lesioned (top) and a sham (bottom) rat recorded at P28–P35. A depolarization is observed in both cases, but no spike firing could be evoked at this early age. c, Responses in an adult-lesioned rat (top) and a sham rat. The adult VH lesion abolishes the VTA-evoked membrane potential depolarization. A depolarization without spike firing is observed in rats that received a sham operation as adults. d, Bar graph comparing duration (Dur) of evoked membrane depolarization, expressed as decay to half amplitude (Amp).Numbers in parentheses indicate the number of recordings. e, Bar graph comparing peak amplitude of VTA-evoked responses among all groups. f, Bar graph comparing the number of neurons exhibiting spike firing in response to VTA stimulation, represented as a percentage. *p < 0.01 (χ2 test).g, NAcc responses to PFC stimulation (arrowhead). An overlay of responses in a neonatally lesioned (top) and a sham (bottom) rat older than P56 is shown. EPSPs were evoked in both cases.h, EPSP responses in a neonatally lesioned (top) and a sham (bottom) rat at P28–P35. i, Similar EPSPs evoked by PFC stimulation in an adult-lesioned (top) and a sham (bottom) rat. j, k, l, Comparisons of PFC-evoked EPSP amplitudes, decay time to half of peak response, and latency among all groups. Numbers inparentheses indicate the number of recordings. No difference could be observed. Dashed lines in alltraces indicate resting membrane potential.