After reaching stable performance, two more difficult mixture contrasts (4% and 2% mixture contrast) were sequentially introduced ( Figure 6A, phase IV). (V)

selleck Rats were returned to a go-signal paradigm with dgo = 1.0 s at 2% mixture contrast and then trained to stable performance on 4% mixture contrast ( Figure 6A, phase V). (VI) RT performance was measured on three easier ratio pairs ( Figure 6A, phase VI). The training sequence consisted of (1) handling and habituation to the behavior box (3 sessions); (2) water-port training (1 day); (3) odor-port training, in which a single odor (usually ethyl butyrate) was rewarded at either port and the required center poke duration was increased from 0 to 300 ms (2–4 sessions); (4) introduction of test odors in 5:95 and 95:5, rewarded at left and right choice ports with assignments counterbalanced across rats (1–3 sessions); (5) introduction of increasingly difficult mixture ratio pairs rewarded at the side corresponding to the dominant component (4–7 sessions). Go-signal task training occurred between phase III and IV. For the check details purpose of experiments involving training on a new stimulus or condition, stable or asymptotic performance was defined as <5% change in performance over ≥5 sessions. All the analysis was performed in Matlab 6.5 Release 13. Behavioral accuracy

was defined as the percentage of correct choices over the total number of correct and incorrect choices. Odor sampling duration (OSD) was calculated as the difference between odor valve actuation until odor port exit, with 100 ms subtracted to account for the delay from valve opening to odor reaching the nose (Feierstein et al., 2006; Figure 1C). Movement time (MT) was defined as the time between odor port exit and choice port entry. We excluded from calculation of performance accuracy and OSD trials in which odor port withdrawal occurred less than 100 ms after odor

onset (<10% of trials) or before the go signal in go-signal paradigms (<25% of trials) and trials in which no choice was made or choice port entry occurred after the response deadline (<1% of trials) (Figure S1E). Performance accuracy as a function of mixture difficulty was fitted with a Weibull function using a maximum likelihood method and OSDs using a linear regression, except in Figure 2Cii where a logistic Farnesyltransferase regression using binomial distribution was used. Logistic regression was also used to fit the psychometric function in Figure 2Ci. Error bars are mean ± SEM (n across rats) or mean ± SD (n across sessions). The effect of difficulty on accuracy or OSD was tested using one-way ANOVA with pairwise comparisons between different mixture contrast ratios (MULTCOMPARE function in Matlab) at a significance level of p < 0.0125 (i.e., adjusted for multiple comparisons). In order to estimate the ability of the subject to anticipate the occurrence of a go signal, we calculated the subjective anticipation function, as described in Janssen and Shadlen (2005).