Model simulations also revealed that the

cbDDM provided a significantly better fit than a stochastic model with collapsing Wnt tumor bounds, when tested against our data from 11 subjects (p = 0.0044, paired t test). With data across two experiments suggesting that humans integrate perceptual evidence over time, we next sought to characterize where this integration occurs in the brain. Although information might be expected to accumulate linearly over time, when the cbDDM is used to simulate the mean accumulated signal for trials of different lengths, it is evident that the time course of integration is nonlinear, increasing more rapidly closer to the time of decision (Figure 5A). Therefore, the behaviorally derived parameters from the cbDDM (including drift rate, diffusion coefficient, and collapse rate) were used, on a subject-by-subject basis, to model the expected temporal profile of information integration. These in turn were used to generate subject-specific fMRI regressors

of interest in an event-related finite-impulse-response ABT-888 chemical structure (FIR) model, enabling us to characterize within-trial temporal changes in the fMRI time series. Note that the absolute value of the integration profile was used to represent evidence toward either decision bound, and only trials of three, four, and five sniffs were included to ensure that sufficient numbers of trials across subjects were available for estimating the imaging data. This approach revealed significant bilateral activity in centromedial OFC (p < 0.05 small-volume corrected), near the anterior-medial portion of area 13l, (following the nomenclature of Ongür et al., Oxygenase 2003), and situated within the putative human olfactory OFC (Gottfried and Zald, 2005) (Figure 5B). To characterize the temporal profile of these activations as a function of trial length, deconvolution techniques (Glover, 1999; Zelano et al., 2009) were used to remove the low-pass effect of the fMRI hemodynamic response function on the mean time series in OFC. These plots show that activity increased at

slower rates for longer trials, peaked at the time of decision, and had lower peaks for longer trials, suggestive of collapsing bounds (Figures 5C and 5D). Statistical analyses demonstrated a main effect of time (sniff number) in OFC (right mOFC, p = 0.007; left mOFC, p = 0.021; repeated-measures ANOVA) and a significant interaction between condition and time in right mOFC (p = 0.032) and at trend level in left mOFC (p = 0.081), demonstrating faster rates of increase for shorter trials. Additionally, a leave-one-subject-out cross-validation technique (Kriegeskorte et al., 2009) was used to obtain unbiased estimates of peak voxel activity in left and right OFC, and resulted in similar time series responses (Figure S2; Supplemental Experimental Procedures). These patterns conform closely to the temporal profiles predicted from the cbDDM model (cf. Figure 5A) and are consistent with olfactory information accumulation in human OFC.