Attentional modulation in human primary olfactory cortex

Abstract

Central to the concept of attention is the fact that identical stimuli can be processed in different ways. In olfaction, attention may designate the identical flow of air through the nose as either respiration or olfactory exploration. Here we have used functional magnetic resonance imaging (fMRI) to probe this attentional mechanism in primary olfactory cortex (POC). We report a dissociation in POC that revealed attention-dependent and attention-independent subregions. Whereas a temporal subregion comprising temporal piriform cortex (PirT) responded equally across conditions, a frontal subregion comprising frontal piriform cortex (PirF) and the olfactory tubercle responded preferentially to attended sniffs as opposed to unattended sniffs. In addition, a task-specific anticipatory response occurred in the attention-dependent region only. This dissociation was consistent across two experimental designs: one focusing on sniffs of clean air, the other focusing on odor-laden sniffs. Our findings highlight the role of attention at the earliest cortical levels of olfactory processing.

Attention to Odor Modulates Thalamocortical Connectivity in the Human Brain

“…Notably, and in contrast to previous findings (Sabri et al, 2005;Zelano et al, 2005), none of the above regions was significantly activated when subjects specifically attended to odor. The main effect of odor attention (collapsed across odor and tone) failed to reveal attention-dependent neural activity anywhere in pPC, aPC, or OFC, or MD thalamus, even at a reduced threshold ( p Ͻ 0.05, uncorrected).…”

“…These physiological findings highlight the efficacy of our attentional manipulation, whereby subjects attended more to odor content when it was relevant for the task (odor attention) than when it was irrelevant (tone attention). Moreover, the data are compatible with previous work showing that human can selectively direct their attention to the olfactory modality (Spence et al, 2001;Zelano et al, 2005).…”

“…Thus, the OFC and olfactory tubercle responded to the presence of an odor only when it was task relevant (e.g., during odor attention), effectively tuning out olfactory sensory information when it had no bearing on the task (e.g., during tone attention). Although the effect in olfactory tubercle was observed at low threshold, it nevertheless converges with previous fMRI findings from other investigators showing that attention to sniff content modulates activity in this particular brain area (Zelano et al, 2005).…”

“…Our model incorporated four lefthemisphere regions [anterior PC (aPC), posterior PC (pPC), MD thalamus, and OFC] to feature the direct and indirect pathways from aPC to OFC. The separation of PC into aPC and pPC subdivisions was based on previously established anatomical and functional heterogeneity of this structure in both animals and humans (Haberly, 2001;Gottfried et al, 2002;Zelano et al, 2005). The VOIs in aPC, pPC, and MD thalamus were first delineated anatomically, with reference to a human brain atlas (Mai et al, 2004).…”

Rapidly acquired multisensory association in the olfactory cortex

“…Thus, the POC, in sync with other olfactory structures, may actively mediate the process of olfaction not only by coding odorant quality, but also by coding prior information about stimuli, thereby determining when the attentional focus shifts from merely breathing in air to smelling the world around us (Wilson 2003; Zelano et al. 2005). …”