Citrus Odour Produces Resilient Response to Cognitive Load and Enhances Performance in the N-Back Task

Background: Olfactory pathway and limbic system demonstrate a close nexus, which paves common ground for investigating the effects of smell on emotions, cognitive load and autonomic functions. Notably, olfactory stimulation during the administration of cognitive load may interfere with the performance. Purpose: The study is planned to investigate the effect of citrus inhalation on cognitive performance, through psychophysiological assessments. Methods: Thirty male participants were subjected to the cognitive load with the 2-back task in control and experimental sessions. Olfactory stimulation was administered with a pure citrus odour through an aroma diffuser. Electrocardiogram (ECG) for heart rate variability (HRV); photoplethysmography (PPG), and electrodermal activity (EDA) were recorded in experimental and control sessions. Results: Citrus odour significantly improved the performance in 2-back task. A paired t-test revealed that the target correct response numbers and target accuracy were significantly increased with the citrus odour inhalation. The EDA showed a rise in the skin conductance level with the 2-back task that was suppressed with the citrus odour administration. The HRV measures, pNN50, RMSSD, and HF power demonstrated a significant increase in the citrus smell. Conclusion: Importantly, citrus odour produced resilience to cognitive stress due to the cognitive task and it was reflected in the EDA. Olfactory stimulation with citrus improved the scores in the 2-back task performance. Though there was no alteration in the overall variability of cardiac oscillation but there was a conspicuous shift of autonomic balance towards the parasympathetic system with the citrus inhalation. The observed finding advocates the use of citrus odour as a cognitive stress-suppressing measure for cognitive enhancement.