Figure 2. Histology and neuron classification. a, Approximate locations of neural recordings in the DMS are indicated by colored boxes (sucrose, top; cocaine, bottom). b, Scatter plots of average spike waveform durations (x, peak duration at half-maximum; y, valley–peak duration) for each single unit recorded in sucrose-experienced rats (top) and cocaine-experienced rats (bottom). c, The approximate proportions and average waveforms superimposed to show interwave variability for classified cell types recorded from sucrose-experienced rats (top) and cocaine-experienced rats (bottom). Dotted line, zero voltage. Scale bar, 100 µs. d, Mean peak duration, valley duration, and session-wide firing rate for MSN and FSI populations recorded from sucrose-experienced rats (top; MSNs: 180 μs, 362 μs, 3.09 Hz; FSIs: 91 μs, 197 μs, 13.48 Hz) and cocaine-experienced rats (bottom; MSNs: 177 μs, 362 μs, 2.33 Hz; FSIs: 90 μs, 177 μs, 10.94 Hz).