Dogs can detect an odour humans emit during epileptic seizures

The new finding gives scientists hope for training seizure alert dogs, which remain controversial and unproven.

By Douglas Main
photographs by Joël Sartore, National Geographic Photo Ark
Published 30 Mar 2019, 08:33 GMT
A Labrador cross.
A Labrador cross.
Photograph by Joël Sartore, National Geographic Photo Ark

Dogs’ miraculous sense of smell allows them to do many things that no human technology can achieve, such as sniffing out drugs, explosives, and even diseases like cancer. Dogs are trained to respond to and even sense epileptic seizures before they occur—though effectiveness varies widely, and there’s been little solid scientific evidence that such a thing is possible. Further, it hasn’t been understood how dogs might be capable of such a feat. Could it be subtle alterations in behavior, movement, or some odorous giveaway?

A new small study suggests that humans emit a specific odour during epileptic seizures that some dogs can recognise.

In a paper published Thursday in the journal Scientific Reports, researchers took sweat samples from seven patients with different types of epilepsy across a range of activities, such as resting, exercising, or having a seizure.

The scientists then placed the sweat samples in cans and showed that five dogs could be trained to recognise which one contained the samples collected during epileptic seizures.

This is the first time that it’s been shown in a published study that humans do emit some odorous chemicals during epileptic seizures, ones that dogs can pick up on. The paper opens the door to future tests or training approaches that might allow dogs to better respond or even sense seizures before they progress, says study lead author Amélie Catala, a doctoral student at France’s University of Rennes.

To be clear, this study uses samples taken during a seizure, not before, and has not identified what these chemicals are or at what point they are released.

“Studies like this are important, to provide a sound scientific foundation for the true capabilities of canines sensing seizures,” says Kenneth Furton, a chemistry professor at Florida International University not involved with the paper who has studied dogs and their olfactory detection abilities.

Furton’s own research aims to take things further. He says that in his own work he has come across a significant number of dogs that can sense a seizure, from anywhere from 15 to 45 minutes before it takes place, potentially allowing the person to take medication to prevent it or lessen its severity.

He and a Ph.D. student show in a forthcoming study that people release a specific group of volatile organic compounds before seizing, which dogs can smell.

There are, however, already a variety of organisations that provide “seizure alert” and “seizure response” dogs, but effectiveness can vary widely. (The former are supposed to pick up on seizures before they occur, while the latter are trained to provide supportive care once they do take place.) Furton is working to develop standards that could be used to train dogs to better respond to or even sense seizures. Currently no such standards exist.

Gary Mathern, the chair for epilepsy research at UCLA’s medical school, emphasizes that the Scientific Reports study was incremental and won’t have immediate impact for training dogs. This process remains difficult, expensive, and lacks uniformity, he adds. But on the positive side, it could lead to new detection mechanisms for seizures or new approaches for studying epilepsy.

Dogs and their incredible sensing abilities deserve more research, Furton says. In some cases, canines can be trained to respond or alert to seizures in as little as a few weeks, though the relationship between the dog and their human is important, and that may take longer.

The study “makes sense... and isn’t surprising,” Furton adds, who’s been working in this field for nearly 25 years. “You can train dogs to alert to almost anything.”


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