Figure 5.
Mixture suppression is common in AOB neurons, particularly those that are selective for MMU. A, Histogram showing subadditivity indices (Isubadditivity, see Materials and Methods) for all 52 cells with sufficient intervals of each stimulus. Negative values indicate subadditivity, while positive values indicate superadditivity. Black indicates cells which showed on average an increase in firing rate in response to both stimuli, while gray indicates cells which showed on average a decrease in firing rate in response to at least one of the two stimuli. B, PSTH of a single AOB neuron showing a subadditive response to the mixture of 1:300 FMU and 1:300 MMU. For this AOB neuron, the response to 1:300 diluted MMU is nearly equal to that to 1:100 diluted MMU, with the response to the mixture lying between these two, suggesting that for this cell, subadditivity might be explained by a saturation of excitation or of firing rate. C, PSTH of a second AOB neuron showing a subadditive response to a mixture of FMU and MMU. For this cell, the response to the mixture is well below the response to 1:300 diluted FMU, ruling out the possibility that this subadditivity could be explained by saturation alone. D, Histogram showing mixture suppression indices (Isuppression, see Materials and Methods) for all 38 cells showing subadditive behavior. Negative values indicate mixture suppression. Colors are as in A. E, Mixture suppression indices plotted as a function of selectivity for FMU; selectivity for MMU is indicated by negative selectivity values. Each point indicates one cell; the highlighted cells indicate the examples shown in B and C, respectively. Small plot on left includes all cells included in D; blow-up on right shows region near and below zero at higher resolution. Most cases of sizable mixture suppression occurred in male-selective neurons (p < 0.05, see Materials and Methods).