In a recent study published in PLOS ONE, researchers used a controlled olfactory paradigm to evaluate whether dogs could discriminate between human odors in breath and sweat samples before and after experiencing experimentally induced negative psychological stress.

Study: Dogs can discriminate between human baseline and psychological stress condition odours. Image Credit: smrm1977/Shutterstock

Background

A stress response is the principal physiological process related to anxiety, panic attacks, and post-traumatic stress disorder (PTSD). Given domesticated dogs’ remarkable sense of smell and their closeness with humans, it is feasible that they might detect changes in human physiology through odor, for instance, olfactory cues related to acute negative stress.

To date, studies have assessed dogs’ detection of human psychological states primarily via emotional contagion, a process that mirrors the emotional states of people.

Sundman et al., for example, reported that the long-term cortisol level of pet dogs mirrors that of their owners. Nonetheless, they might not discover the mechanisms employed by dogs to detect their owner’s stress. Perhaps, dogs picked a mix of verbal, visual, and olfactory cues. Likewise, D’Aniello et al.’s study suggested that dogs could detect human psychological states primarily from olfactory cues. One other recent study by Reeve et al. found that trained Medical Alert Dogs were most aware of stress.

Yet, a controlled olfactory study addresses whether dogs can discriminate between human odor samples taken when not under stress and when under stress.

In regards to the study

In the current study, researchers used a bio-detection paradigm to point out how trained dogs can discriminate between odors in several samples in a controlled setting. To date, these paradigms have been mostly used concomitantly with non-human odors, e.g., amyl-acetate, and isoamyl-acetate. Integrating most of these paradigms into the sphere of dogs detecting human chemosignals might be interesting.

They collected a complete of 13 participants’ data remotely. To this end, they delivered sample kits to every participant’s homes, and the experimenters conducted the stress induction protocol over Microsoft Teams or Zoom. They contacted participants via email with a gathering and a web based survey link.

Participants self-confirmed via a survey questionnaire that they were non-smokers and had not consumed food or drink, apart from water, or any mood-altering medication, for at least one hour before the meeting. Participants answered demographic questions within the survey, including their age, gender, and ethnicity.

The researchers demonstrated the right way to make their baseline sample by wiping a chunk of gauze on the back of their neck, placing it within the vial labeled D1, after which exhaling deeply into the vial thrice before securing the lid. The team asked the participants to finish a Mental Arithmetic Task (MAT), where they counted backward from 9000 in units of 17 without using paper or a pen. The duty continued for 3 minutes, whatever the variety of correct answers.

Once sample collection was complete, they instructed participants to finish the second self-report measure, which assessed their post-task level stress using a self-report measure termed a visible analog scale (VAS). An additional 40 participants accomplished the protocol on campus and in person, with the addition of physiological measures for 25 of 36 samples.  All samples that passed the standards of a two-point increase in self-report stress from the self-report VAS and a rise within the mean heart rate (HR) and mean arterial pressure (blood pressure: BP) were shown to dogs.

The team trained dogs on a two-phase, three-alternative forced-choice paradigm with increasing difficulty levels. They made them discriminate against odor between two people after which for a similar person at two times of the day. Each dog carried out 20 discrimination trials inside each session to evaluate its ability to discriminate between the samples.

Dogs with above likelihood performance of 80%  progressed to the testing stages. This sequential method allowed researchers to be sure that if a dog’s performance dropped to likelihood on the testing stage, it happened since the stress and baseline samples were indistinguishable from the dog.

The researchers imposed strict odor controls. For instance, they collected samples from each participant in the identical room at 4 minutes intervals, which reduced the potential for dogs having the ability to inform their indication decisions by utilizing background volatile organic compounds (VOCs) from the air within the room.

Study findings

The dogs’ performances were consistently above likelihood, ranging between 90% to 96.88% during discrimination tests, with an aggregate performance of 93.75% across sessions. Also, dogs were in a position to discriminate between them on first exposure. No dog showed signs of distress when encountering the human stress samples. Quite the opposite, dogs appeared excited once they got here to the stress sample in anticipation of the clicker and food reward for an accurate alert.

Each participant’s samples were distinct at baseline in comparison with after the stress induction. Dogs also recognized that the baseline sample (D1) was distinct from what they were previously rewarded for. The dogs successfully passed the primary trial of every discrimination phase session and appropriately alerted to the stress sample in 94.44% of first exposure trials. They incorrectly alerted on the baseline sample of their first exposure only twice. Dogs recognized that the brand new stress sample (T2) was the identical odor profile utilized in the educational trials (T1).

Conclusions

The present study evidenced that dogs can detect an odor related to acute stress in humans from breath and sweat alone. This finding laid a powerful foundation for future investigations into emotional contagion since it confirmed that an odor component to acute negative stress might be detected by dogs within the absence of visual or vocal cues.

Notably, it was a proof of principle study, with study samples comprising only 4 dogs; nonetheless, this didn’t compromise the study findings. It demonstrated that some highly trained dogs could successfully discriminate between samples from different humans. Furthermore, a small variety of dogs could detect odor differences in baseline and stress samples, which suggested that an odor difference existed.