Familiarity and concentration- based intensity shape spatial patterns of odor-evoked brain activation

Olfactory perception is shaped by both the physical properties of odorants and prior odor experience. Odor familiarity and concentration-based perceptual intensity are known to influence neural responses; however, less is known about how odor-evoked brain activation varies across conditions that differ in familiarity and perceived strength. Using functional magnetic resonance imaging, fMRI, we examined condition-specific activation patterns and brain-behavior relationships during passive odor perception. Sixty-three healthy young women participated in a 2 × 2 factorial fMRI experiment including familiar and unfamiliar odors presented at low- and high-intensity concentrations. Odors were delivered birhinally using a computer-controlled olfactometer, and participants provided in-scanner ratings of perceived odor intensity and odor-evoked memory intensity. Whole-brain analyses were used to describe condition-wise activation maps and direct between-condition contrasts, while region-of-interest analyses focused on canonical olfactory, limbic, and memory-related regions. All odor conditions elicited activation across olfactory, limbic, frontal, parietal, and cerebellar regions. Direct contrasts showed that low-intensity unfamiliar odors elicited greater activation than low-intensity familiar odors in frontal and parietal regions, suggesting increased evaluative processing when weak odor input could not be readily matched to established odor representations. Low-intensity unfamiliar odors also elicited greater activation than high-intensity unfamiliar odors in precuneus and supramarginal/angular regions. Brain-behavior analyses showed significant associations only for familiar odors presented at low intensity, where subjective memory intensity was negatively correlated with bilateral parahippocampal activation. These findings suggest that odor familiarity and concentration-based intensity contribute to condition-specific patterns of odor-evoked brain activation, with low-intensity familiar odors revealing a selective relationship between odor-evoked memory experience and medial temporal responses.