“Smell is a potent wizard that transports you across thousands of miles and all the years you have lived.” — Helen Keller
There is something uniquely intimate about the sense of smell. Unlike vision or hearing, olfactory signals travel a remarkably direct neural route from receptors in the nasal epithelium through the olfactory bulb, and straight into the brain’s limbic system, the seat of emotion and memory. A single scent can transport us instantly to a childhood kitchen, sharpen our alertness, or dissolve stress within seconds. Yet for all its power, olfaction has historically been one of the most understudied human senses. That landscape is changing. A new generation of multimodal brain-body research platforms, capable of simultaneously recording signals from the brain and the body, is giving scientists insight into how smell shapes thought, emotion, and cognition.
The olfactory system is the only sensory system that bypasses the thalamus, the brain’s central relay station, and connects directly to the amygdala and hippocampus, two structures critical to emotional processing (affect) and memory. This anatomical shortcut explains why odors are so potent at triggering emotional memories, often more vividly than visual or auditory cues. Beyond memory, researchers are increasingly interested in how odor exposure alters measurable physiological and neurological states in real time, ranging from modulating cognitive performance and stress to the early detection of neurodegenerative disease, in which olfactory dysfunction often appears years before other symptoms emerge.
What makes this research technically challenging is also what makes it scientifically rich: the olfactory experience simultaneously engages the central nervous system and the autonomic nervous system, meaning that studying it well requires capturing signals from both brain and body at once. Electroencephalography (EEG) provides direct data on the brain’s electrical activity with millisecond-level temporal resolution, making it well-suited to detecting rapid shifts in cognition and arousal following odor exposure. Functional near-infrared spectroscopy (fNIRS) offers a complementary picture, using near-infrared light to detect changes in cortical oxygenation, a measure of the brain’s metabolic response to stimulation. Wearable and tolerant of movement, fNIRS is particularly well-suited to naturalistic experimental designs. Electrodermal activity (EDA), or skin conductance, captures the autonomic nervous system’s arousal response through sweat gland activity, while electrocardiography (ECG) and heart rate variability (HRV) add a cardiovascular layer that can distinguish sympathetic from parasympathetic activity in fine detail. Today’s lab setups use a range of sophisticated scent delivery systems to integrate precise, controllable olfactory stimuli into experiments. The real power of modern multimodal platforms lies in their ability to synchronize all these channels within a single setup, time-locking each physiological response to a specific odor event and revealing the full brain-body picture that no single signal could show alone.
A research team at the All India Institute of Medical Sciences in Jodhpur investigated whether citrus odor could buffer the cognitive and physiological impact of working memory load. Thirty participants completed a demanding working memory test under both control and citrus-odor conditions, with the odor delivered via an aroma diffuser. ECG, photoplethysmography (PPG), and EDA were recorded using a BIOPAC data acquisition system with AcqKnowledge software for analysis, and dual-signal BioNomadix wireless EDA and PPG module. For EDA recording, disposable silver/silver chloride disc electrodes were applied to the hypothenar and thenar eminences, and the PPG sensor was placed on the index finger. Citrus odor significantly improved task accuracy while suppressing the rise in skin conductance typically associated with cognitive load. HRV measures, including pNN50, RMSSD, and HF power, shifted toward parasympathetic dominance, indicating a calmer, more regulated physiological state. The findings, published in the Annals of Neurosciences, suggest that citrus odor acts as a cognitive stress buffer and point to practical applications in educational, occupational, and clinical settings with high sustained cognitive demands.
A counterintuitive question motivated a study at Nagaoka University of Technology in Japan: could black pepper, widely known as a stimulant, actually calm the body’s stress response? A group of university students performed a 30-minute arithmetic calculation task under three aroma conditions: black pepper, ginger, and a scentless control. Scents were delivered at precise, reproducible intervals through an olfactometer. A BIOPAC data acquisition system recorded continuous ECG and skin conductance level (SCL) at 200 Hz with 16-bit resolution, with high-frequency HRV (HF-HRV) derived as a measure of cardiac parasympathetic activity. Electrodes were placed beneath the right clavicle and on the lower left abdomen following the Lead II placement protocol for ECG measurements using multi-lead ECG cables. SCL was recorded using skin conductance sensors placed on the palmar side of the middle phalanx of the index and ring fingers of the participant’s non-dominant hand. The results, published in the Journal of Physiological Anthropology, found that black pepper aroma reduced the stress-induced rise in heart rate by 38.9% compared to the scentless control, attenuated the decline in HRV by 32.9%, and blunted the increase in SCL compared to ginger. Crucially, subjective stress ratings did not differ across conditions, demonstrating that the body can respond to olfactory stimuli at a physiological level even when conscious perception does not register a difference. These findings have meaningful implications for workplace wellness and aromatherapy research.
A French consortium of researchers from the Université Bourgogne Franche-Comté and the Université Grenoble Alpes tested whether music, lavender odor, or their combination would accelerate autonomic recovery following acute cognitive stress. Ninety-nine participants completed a battery of cognitively demanding tasks. They were then randomly assigned to one of four 30-minute recovery conditions: silence, relaxing classical music, lavender essential oil, or music and lavender together. A data acquisition system running AcqKnowledge continuously recorded ECG and EDA using Ag-AgCl finger electrodes, with HF-HRV as an index of parasympathetic activity and EDA as a measure of sympathetic arousal. Published in Psychophysiology, the study found that both music and lavender independently facilitated autonomic recovery. The surprising finding, however, was the absence of any multisensory advantage: combining the two stimuli produced no greater benefit than either alone, suggesting that when multiple sensory channels converge on the same relaxation goal, they may share rather than combine their neural resources. The study underscores both the value of multimodal physiological recording in parsing the mechanisms of stress recovery and the importance of rigorously testing assumptions about how the senses work together.
These studies illustrate how much remains to be discovered at the intersection of smell, brain, and body, and how essential it is to measure all three at once. As synchronized multimodal platforms continue to evolve, the science of olfactory cognition continues to shape our fundamental understanding of how the brain works and the development of practical tools to support cognitive health and wellbeing. To learn more about the convergence of olfaction with brain-body research, be sure to check out our webinar on how scents influence cognition.
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