Detection of Target Odorants in Odor Mixtures Among Healthy Individuals and Patients with Olfactory Dysfunction

Academic Background

In daily life, most of the odors we encounter are mixtures rather than single odorants. However, the mechanisms underlying human perception of odor mixtures are far less understood than those of single odorants. The perception of odor mixtures can be divided into two modes: analytical perception and configural perception. Analytical perception refers to the ability to discern individual components within a mixture, while configural perception refers to the perception of the mixture as a unique odor distinct from its components. Although studies have shown that certain odor mixtures are perceived configurally across various species, the mechanisms of human perception of odor mixtures remain largely unexplored.

Previous research has indicated that identifying individual odorants in mixtures becomes more challenging as the number of components increases. Humans can typically identify up to three or four components in a mixture, and this limit appears to be independent of odor type or individual training experience. However, research on the ability of humans to detect target odorants in complex mixtures remains limited. This study aims to investigate the ability of healthy individuals and patients with olfactory dysfunction to detect target odorants in odor mixtures and to compare the differences between the two groups.

Source of the Paper

This paper was co-authored by Eva Drnovsek, Kristina Weitkamp, Venkatesh N. Murthy, Edanur Gurbuz, Antje Haehner, and Thomas Hummel. The authors are affiliated with the Smell and Taste Clinic at the Department of Otorhinolaryngology at Technische Universität Dresden in Germany, the Center for Brain Science and the Department of Molecular and Cellular Biology at Harvard University in the USA, and the Faculty of Medicine at Mugla Sitki Kocman University in Turkey. The study was funded by Volkswagenstiftung and published in the European Journal of Neuroscience in 2025.

Research Process

Participants and Grouping

The study included 90 healthy individuals (control group) and 40 patients with olfactory dysfunction (patient group). All participants were at least 18 years old and excluded from having significant health conditions that might affect olfactory function, such as diabetes, Parkinson’s disease, or renal insufficiency. The control group was recruited through flyers, while the patient group was recruited from the outpatient clinic of the Smell and Taste Clinic at Technische Universität Dresden.

Olfactory Function Assessment

All participants completed questionnaires on sociodemographic data and subjective olfactory function. The patient group underwent a thorough clinical evaluation, including a structured medical history and an extended version of the Sniffin’ Sticks olfactory test. This test assessed participants’ odor threshold (T), odor discrimination (D), and odor identification (I), which were combined into a TDI score. Based on the TDI score, participants were classified as normosmic (normal olfactory function), hyposmic (reduced olfactory function), or anosmic (loss of olfactory function). The control group was assessed using only the odor threshold and odor identification tests.

Target Odorant Detection Tasks

The study designed two tasks to evaluate participants’ ability to detect target odorants in odor mixtures. The target odorants for all participants were eugenol and phenylethanol (PEA), with a third target odorant randomly assigned. Each task consisted of four steps, with the number of components in the odor mixture increasing from two to seven or eight. In each step, participants were asked to select the sample containing the target odorant from multiple options.

• Task 1: Participants selected the sample containing the target odorant from three options, two of which were background odors and one was a mixture containing the target odorant.
• Task 2: Participants selected the sample containing the target odorant from two options, both of which were odor mixtures, but only one contained the target odorant.

Odor Selection and Mixture Preparation

The study selected 10 monomolecular odorants, including eugenol, phenylethanol, eucalyptol, heptanol, and others. These odorants were diluted to comparable intensities to avoid certain odors overpowering others due to higher intensity. Odor mixtures were prepared by soaking the odorants in gauze pads and placing them in brown glass jars.

Key Findings

Target Odorant Detection in Healthy Individuals

The results showed that the success rate of detecting target odorants in healthy individuals decreased as the number of components in the mixture increased. However, even in mixtures containing seven or eight components, approximately 50% of healthy individuals could detect eugenol, and 30%-40% could detect phenylethanol. Notably, the detection success rates for certain odorants, such as citronellal and hexenol, were significantly higher than for others, such as melonal and pinene.

Comparison Between Patients and Controls

Compared to the healthy control group, patients with olfactory dysfunction had significantly lower success rates in detecting eugenol and phenylethanol. In steps with more mixture components, the detection success rates of the patient group approached chance levels. Additionally, the study found that the ability to recognize target odorants was closely related to detection success rates. Participants who could clearly identify the target odorants had significantly higher detection success rates than those who could not.

Relationship Between Olfactory Function and Detection Ability

The study further analyzed the relationship between task scores and olfactory function. The results showed that task scores were significantly positively correlated with odor threshold and odor identification abilities, indicating that target odorant detection tasks could be used to assess individual olfactory function.

Conclusions and Significance

This study confirmed that healthy individuals can detect target odorants in mixtures containing up to eight components, with detection success rates significantly higher than chance levels. The ability to detect target odorants was influenced by the target odorant itself, the number of components in the mixture, individual olfactory function, and the ability to recognize the target odorant. Furthermore, patients with olfactory dysfunction performed significantly worse than healthy controls in detecting target odorants, suggesting that target odorant detection tasks could serve as an effective tool for evaluating olfactory function.

Research Highlights

1. Novel Research Design: This study is the first to systematically evaluate the ability of healthy individuals and patients with olfactory dysfunction to detect target odorants in complex odor mixtures, filling a gap in this field of research.
2. Clinical Application: The findings suggest that target odorant detection tasks can be used to assess olfactory function, providing a new method for diagnosing olfactory dysfunction.
3. Insights into Odor Perception Mechanisms: The study highlights the importance of target odorant recognition in the perception of odor mixtures, offering valuable clues for further research into odor perception mechanisms.

Additional Valuable Information

The study also explored the impact of perceptual properties of odorants (e.g., intensity, pleasantness, familiarity) on detection success rates but found no significant differences. Future research could expand the sample size and include more types of odorants to validate the conclusions of this study.

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Through this research, we have gained a deeper understanding of the human ability to detect target odorants in complex odor mixtures, providing new insights for the diagnosis and treatment of olfactory dysfunction.