He concluded that “rabbits smell what they expect, not what they sniff.” More recent electrophysiological recordings in rodents have identified prestimulus anticipatory events not only in the bulb, but also in piriform cortex and orbitofrontal cortex (Kay and Freeman, 1998 and Schoenbaum and Eichenbaum, 1995), implying http://www.selleckchem.com/products/AG-014699.html that well before an odor arrives, much of the olfactory system generates a prediction about the upcoming stimulus. Finally, in human piriform cortex, attention to olfactory

content evokes baseline deviations in fMRI activity (Zelano et al., 2005), although it is unclear whether these changes merely reflect a general attentional see more gain or reflect feature-based predictive codes about specific odors. Olfactory studies in humans and other animals increasingly show that cortical representations of odor in piriform cortex are encoded as spatially distributed ensembles (Freeman, 1979, Haberly, 1985, Haberly, 2001, Hasselmo et al., 1990, Howard et al., 2009, Illig and Haberly, 2003, Kay and Stopfer, 2006, Martin et al., 2004, Spors and

Grinvald, 2002, Stettler and Axel, 2009 and Wilson and Stevenson, 2003) evolving over a time span of seconds (Rennaker et al., 2007). Therefore, on the basis of these observations, we combined an olfactory attentional search task with functional magnetic resonance imaging (fMRI) techniques and pattern-based multivariate analyses to test three Dipeptidyl peptidase hypotheses following from the predictive coding model: (1) odor-specific predictive codes in the human olfactory brain are established prior to stimulus onset and take the form of spatially distributed templates or “search images”; (2) ensemble activity patterns should evolve in space and time over the course of a trial, such that predictive coding gives way to stimulus coding from pre- to postodor onset; and (3)

a legitimate prestimulus predictive template should be able to predict olfactory behavioral performance in the post-stimulus period. Subjects participated in a simple olfactory fMRI task in which they decided whether a particular predetermined target smell was present on each trial. In target A runs, subjects determined whether odor A was present, and in target B runs, subjects determined whether odor B was present. Stimuli consisted of odor A alone (A), odor B alone (B), or a binary mixture of odors A and B (AB), resulting in six conditions: target A with stimulus A, B, or AB (A|A, A|B, A|AB), and target B with stimulus A, B, or AB (B|A, B|B, B|AB) (Figure 1). Importantly, the physical characteristics of the stimuli were identical across runs, ensuring that the only differing aspect between target A and target B runs was the attentional focus of the subject.