The human-dog relationship started long ago. Archaeological evidence suggests that dogs were the first animals domesticated by humans more than 30,000 years ago. Now, a recent study published in PLOS states that dogs can detect the physiological processes associated with psychological stress in humans with an accuracy of 93.75 per cent.

Dogs have a remarkable sense of smell. As part of the study, researchers analysed whether dogs could sense the chemical signals associated with a person's psychological state. Samples of breath and sweat from non-smokers who had not eaten or had water recently were used for the study. The samples were collected before and after a stress-inducing arithmetic activity. The study participants were asked to report their stress levels, and physiological measures like heart rate and blood pressure were also collected. The samples from 36 participants who experienced increased stress levels and had reported an increase in heart rate and BP were then shown to trained dogs within three hours of being collected.

As part of the study, researchers trained four dogs of different breeds and breed mixes using a clicker and kibble (a training technique that tells the dog which behaviours are rewarding) to match different odours in a discrimination task. The dogs were then asked to identify the stress sample of participants from a group of samples that contained the same person’s relaxed sample, too. The dogs could detect and show alert behaviour on stress samples in 675 of 720 trials. The study gave proof that dogs can identify an odour associated with the change in volatile organic compounds produced by the human body during stressful situations.

Tumours also produce volatile organic compounds, which are seen in the patient’s urine, sweat or breath. These compounds are thought to have a distinct odour, especially in the early stages of cancer. In the last decade, there have been multiple studies suggesting that dogs could be trained to detect these compounds. Experiments conducted by institutions like the University of Pennsylvania Veterinary School’s Working Dog Center and Medical Detection Dogs in the United Kingdom have shown that dogs can detect breast and lung cancer by sniffing the breath of patients; bladder and prostate cancer by sniffing the urine; colorectal cancer by sniffing the patient’s exhaled breathing and stool samples; ovarian tumours by sniffing the patient’s tumour and blood samples; and cervical cancer by sniffing the patient’s biopsy samples.

A lot of research is happening to develop and perfect sensors and nanotechnology that mimic dogs’ superior sense of smell to detect odorant changes in the cells of cancer patients. For instance, the Israel Institute of Technology’s two types of NA-NOSEs―nano artificial noses to validate the efficacy of devices to detect specific odorants in the breath of cancer patients―are under clinical trial. Similarly, MIT’s Centre for Bits and Atoms is working with Medical Detection Dogs to develop ways to train artificial intelligence to detect odours associated with prostate cancer.

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