Characterizing Olfactory Binary Mixture Interactions in Fischer 344 Rats Using Behavioral Reaction Times

Abstract

Response times provide essential subthreshold perceptual data that extend beyond accuracy alone. Behavioral reaction times (RTs) were used to characterize rats' ability to detect individual odorants in a series of complimentary binary odorant mixture ratios. We employed an automated, liquid-dilution olfactometer to train Fischer 344 rats (N = 8) on an odor identification task using nonreinforced probe trials. Binary mixture ratios composed of aliphatic odorants (citral and octanol) were arranged such that relative contributions of the 2 components varied systematically by a factor of 1% (v/v). Odorant concentrations for the target (S+), control (S-), and mixture (S+:S-) odorants were presented relative to threshold for each rat. Rats were initially trained to respond by licking at a spout to obtain liquid reward for either citral or octanol as the reinforced target (S+) odorant. After achieving 100% accuracy, rats were transferred to variable ratio (VR 2) reinforcement for correct responding. Nonreinforced probe trials (2 per block of 22 trials) were tested for each mixture ratio and recorded as either S+ (rats lick-responded in the presence of the mixture) or S- (rats refrained from licking), thereby indicating detection of the trained, S+ odorant. To determine the perceived salience for each ratio, RTs (latency from odorant onset to lick response) were recorded for each trial. Consistent with previous studies, RTs for both odorants were shortest (~150-200ms) when the probe trials consisted of a single, monomolecular component. Binary mixtures that contained as little as 1% of the S-, nontarget odorant, however, were sufficiently different perceptually to increase behavioral RTs (i.e., rats hesitated longer before responding); RTs changed systematically as a function of the binary ratio. Interestingly, the rate of RT change was dependent on which odorant served as the S+, suggesting an asymmetric interaction between the 2 odorants. The data demonstrate the value of behavioral RT as a sensitive measure of suprathreshold perceptual responding.

Decline of prefrontal cortical-mediated executive functions but attenuated delay discounting in aged Fischer 344 × brown Norway hybrid rats

“…Previous studies using operant procedures have shown that latency to respond on a choice trial tends to reflect the certainty of the choice, with subjects taking more time to respond on incorrect compared to correct trials (Abraham et al, 2012, 2004; Higgins et al, 2007; Yoder et al, 2015), and choice latency has been shown to increase with choice uncertainty (or decreased confidence) in humans (Rutishauser et al, 2015). In addition, given that both slower reaction times and reduced speed of processing have been reported in aged subjects (Grottick and Higgins, 2002; Muir et al, 1999), analysis of response latencies could help identify the extent to which accuracy differences in aged rats are influenced by reaction speed or other nonmnemonic factors.…”

“…Interactions among age, delay, and reward type were observed, however, such that young rats generally showed shorter latencies to choose the small, immediate reward whereas aged rats showed shorter latencies to choose the large, delayed reward. Response latencies have been suggested to reflect the incentive properties of rewards, and to represent a more sensitive measure of preference compared to evaluation of discrete choices (Abraham et al, 2012, 2004; Higgins et al, 2007; Schoenbaum et al, 2004; Yoder et al, 2015). The fact that aged rats’ large reward latencies were unchanged by delay (as opposed to young rats, for which large reward latencies were greater at long than short delays) suggests that the incentive properties of the large reward remained high even when delay intervals were long and the large reward was less frequently chosen than the small reward.…”

Awake, long-term intranasal insulin treatment does not affect object memory, odor discrimination, or reversal learning in mice

“…Animals were given a maximum of three blocks (or 60 trials) on four sequential dilutions of 5% ethyl acetate. Similar to that formulated by Yoder et al (2014, 2015) [83,84], odor threshold was recorded as the lowest concentration at which the mouse achieved ≥80% on 1 of 3 consecutive blocks. If a mouse did not reach odor threshold on the four sequential dilutions, it was assigned a threshold of 0.0005% EA.…”

Interaction between age and perceptual similarity in olfactory discrimination learning in F344 rats: relationships with spatial learning

“…The behavioral apparatus and methods employed in this study are identical to those used in our previous work (Yoder et al, 2014, 2015), and detailed descriptions of the training and testing techniques can be found in those previous publications. The olfactometer was connected to a 21-cm deep, 30.5-cm wide, and 24.1-cm tall, ventilated Plexiglas operant chamber.…”