Figure 4. The duration of inhibition of VTA DA neurons depends on a level of conditioned fear. A, Population peristimulus time histograms (100 ms bin) illustrating the responses of 10 DA neurons to the CS+ and CS− during the initial six trials that were characterized by stable respiratory responses to the CS+ in discriminating rats. B, The correlation between the duration of inhibitory pauses in the activity of DA neurons (n = 10) and the increase in respiratory rate during presentations of the CS+ (7–13 trials) evoking partial extinction of respiratory responses in discriminating rats. The correlation is expressed by a linear regression: y = 0.3398 + 0.0792x; F = 160.05, p < 0.0001, df = 1, 67. C, The correlation between the duration of inhibitory pauses in the activity of a DA neuron and the increase in respiratory rate in one non-discriminating rat (y = 0.92070 + 0.03207x; F = 13.02, p = 0.0112, df = 1, 8). D, The lack of correlation between the duration of inhibitory pauses in the activity of DA neurons (n = 4) and the increase in respiratory rate in four non-discriminating rats (y = 1.694 + 0.007x; F = 1.180, p = 0.2837, df = 1, 41). Each black square represents one trial without shock delivery.