66, p = 0.01). By comparison, prestimulus ensemble patterns in APC and OFC had no demonstrable relationship to behavior (p’s > 0.07), indicating that the availability of predictive codes for guiding olfactory perceptual decisions specifically
resides in PPC. Recent theoretical models of sensory perception (Friston, 2005b and Rao and Ballard, 1999) place high importance on hierarchical processing and prediction error: predictions reflect the top-down flow in the cortical hierarchy while prediction error reflects the bottom-up flow of afferent sensory information. Interestingly, findings from univariate fMRI analyses commonly show that an expected (versus unexpected) percept elicits lower selleck chemical mean activity in sensory-related regions, a differential effect that has been attributed to prediction error signaling (Summerfield and Egner, 2009). Therefore, we conducted a complementary univariate imaging analysis to look for evidence of error signaling in our data (Figure 7). fMRI activation in MDT was significantly reduced in response to expected trials compared to unexpected trials (T11 = 2.41, p < 0.03), suggesting this region may participate in generating a prediction error signal. By comparison, there were no significant differences in APC, PPC, or OFC (p's > 0.2). The vast majority of natural, Ponatinib cost real-world odors are encountered in the presence of other competing smells. Thus, on any given inhalation, the
olfactory system faces the challenge of disambiguating salient odor objects from other odors present in the background
(Linster et al., 2007). On top of this challenge, human olfactory perception is both temporally and spatially impoverished (Sela and Sobel, 2010), implying that attentional capture may be insoluble for the olfactory system (Laing and Glemarec, 1992). By utilizing fMRI multivariate analyses in conjunction with an odor search task, we were able to show that odor-specific ensemble patterns emerge prior to odor stimulation and (in PPC) reliably predict subsequent behavioral performance. These findings provide robust evidence for object-based attentional mechanisms that directly impact on odor perception. Separation of the fMRI time series into pre- and poststimulus bins enabled us to identify ensemble patterns of activity both before and after odor arrival. no Before the sniff and in the absence of odor, olfactory ensemble codes in APC and OFC were specific for the attended odor target, rather than being a general effect of attention, indicating that subjects can generate feature-specific information about an odor prior to its receipt. After odor onset, target-related patterns in APC and OFC persisted for up to several seconds, irrespective of the actual identity of the delivered odor. These findings indicate that the ensemble activity in APC and OFC more closely resemble what is being sought-out rather that what is being delivered to the nose.