Figure 4.

In the AON, the suprathreshold response to an effective mixture differed from the linear sum of the suprathreshold responses to all individual components in that mixture. For each of nine AON neurons, the evoked suprathreshold response to an effective mixture (cross) is compared with the suprathreshold responses to the odorants in that mixture (open circles), the sum of all of these individual odorant responses (filled circles), and the sum of only the individual odorant responses that involved a positive change in firing rate (diamonds). In most cells (1–6), the suprathreshold response to the mixture exceeded either of the linear sums, whereas in the other three cells (7–9), the mixture-evoked response was less than or equal to the linear sums. In all cases, the odor-evoked firing rate was calculated relative to presentation of the vehicle alone (i.e., mineral oil) to control for any flow rate and/or vehicle-dependent changes in firing rate in these AON neurons (see Materials and Methods).