Limonene Modulates Event-Related Potentials in a 2-Back Working Memory Task

Olfactory inputs can influence visual cognition. However, it remains unclear whether such effects are driven by the chemical properties of odorants or by mood-related associations, especially under conditions of high cognitive demand. This study examined whether limonene, a key citrus odorous compound, modulates cognitive processing during a visual 2-back task under different levels of perceptual load.

We developed a 2-back working memory task using color lightness discrimination. The task included both low-load (orange) and high-load (gray) conditions. Participants wore a non-woven mask impregnated with the odor solution and performed the task under two odor conditions: limonene exposure and no odor. An electroencephalogram was recorded to evaluate P300 amplitude at central (Cz) and parietal (Pz) electrodes.

Behavioral results, analyzed using signal detection theory, showed that the correct response rate and sensitivity index (d') were higher for orange than for gray stimuli, regardless of the odor condition. Event-related potential (ERP) analysis revealed a significant interaction; under the limonene exposure condition, P300 amplitudes were reduced for gray stimuli, but remained stable for orange stimuli.

Our findings indicate that limonene modulates neural markers associated with attentional and decision-related processing, particularly under high cognitive demand, without clear effects on behavioral performance. The observed P300 suppression suggests that this component may be sensitive to decreases in attentional allocation that behavioral measures failed to detect. Moreover, these results replicate and extend previous findings of limonene-induced P300 suppression, supporting the reproducibility of limonene's modulatory effect on neural markers of cross-modal attentional processing.