Training Dogs to Sniff Out Cancer

Did you know that your human nose contains about six million olfactory receptors, just enough to detect the garlic in spaghetti sauce or tell when the milk has gone bad? In contrast, your dog’s nose has about 300 million such receptors. She can smell the garlic from miles away and discern the spoiled milk before you open the fridge.

A dog’s sense of smell is a tremendous asset and major source of information about the world around them. But that highly developed talent can also be put to use to benefit us “smell-challenged” humans. One of the most intriguing forms of animal-to-human assistance is in the detection of cancer.

Identifying Organic Compounds

In the animal kingdom, odors emitted from a body convey information about their metabolic and psychological status. The human body emits a wide array of volatile organic compounds (VOCs), both odorous and non-odorous. Pathological processes, including cancer cell growth and diffusion, also influences odor signatures. The synthesis of aberrant proteins and altered cell metabolism produces VOCs that differ from these emanating from healthy cells. Thus, VOC identification can become an indicator of an individual’s health status.

Training Dogs to Identify Cancer Samples

Cancer-sniffing dogs are exposed to biological samples (including urine, sweat and breath) and trained to stop and sniff those with unusual VOCs and ignore the others. They then signal to the trainer (often by sitting in front of the positive samples). This training incorporates both stimulus-response and operant response. Stimulus-response occurs when a dog encounters an interesting odor, as when your pooch wants to stop and sniff at the liquid messages other dogs have left on trees and telephone poles. When dogs signal back to a trainer that they have found an interesting smell, they are displaying an operant response.

Speaking the Dog’s Language

Dogs are trained to perform operant responses in ways that have meaning to trainers – sitting, for example, in front of a positive biological sample and walking past a negative sample. However, that’s not how dogs behave in the wild. They may nose, chew or paw at an object that gives off an enticing aroma, but they rarely just sit down near it.

In essence, the operant behaviors they’ve been taught to execute are a foreign language to dogs, developed for the convenience of humans but not reflective of dogs’ inherent behaviors. Performing non-instinctive actions imposes a cognitive and physical load on the animals, which may cause them to delay their actions, give ambiguous signals or make mistakes. Knowing this, researchers in the U.K. decided to look for signaling approaches more consistent with how dogs naturally behave.

Introducing Dog-Friendly Technology

Courtesy: In Situ Foundation and AKC

The researchers addressed the problem by using technology that reduces or eliminates the need for dogs to display an operant response to what they smell in biological samples. They first looked closely at how dogs spontaneously react to enticing smells, observing the animals’ instinctive canine signaling language. In simple terms, they used technology to track and quantify sniffing behavior. Dogs, it turns out, spend more time sniffing interesting smells and get closer to the stinky object, often touching or pressing on it. Using a touch plate and sensor arrangement (no, the dogs didn’t need to paw a keyboard – that job is reserved for your cat), the researchers could monitor the degree and duration of contact between the dog’s nose and the sample container. They found that the pups invested more energy and interest in positive samples, spent more time nosing them and pushing harder on the touch plate. They tended to quickly dismiss the negative samples and move on to something that smelled more interesting.

Giving Dogs their Honest Voice

Whereas a dog’s operant response is a learned, foreign signal convenient for the trainer, her stimulus-response is an honest representation of what the canine is actually perceiving. The shift from trainer interpretation to technology intervention allows the dog to communicate in her own voice, reducing detection errors on the part of the animals and interpretation errors on the part of the humans.

In effect, the U.K. researchers shifted the focus from what humans are capable of reading in canine behavior to an emphasis of what pooches express in their own terms. They made the process dog-centric rather than human-centric. The more natural (and therefore, successful) canine disease detection becomes, the more human lives can be saved. It’s just one more way dogs are really humans’ best friends.