What do dogs think about their owner’s smell? Unfortunately, we can’t ask them. So instead, researchers at Emory University, USA decided to find out what happens inside a dog’s brain when it smells a familiar human.
The team studied a group of 12 dogs who underwent brain scans with a MRI device: this allows their brain activity to me measured safely and noninvasively. The dogs learned to climb inside the MRI scanner and then lie very still so that the images were not blurred, all the while wearing ear muffs so that the sound of the scanner did not disturb them.
The researchers prepared gauze pads with various smells. One was taken from a familiar human, but not the one that had walked the dog to the experiment. This meant that it had to rely on memory to recognise its human friend. Another was taken from an unfamiliar human that the dog had never met. The researchers also prepared two more pads: one with the smell of a familiar dog from their household, and another from an unfamiliar dog. The human smells were obtained from the armpits (without deodorant) and the dog smells from – where else? – their derriere.
Once inside the scanner, the dogs sniffed the gauze pads and the researchers monitored their brain activity. They paid particular attention to two areas: the ‘olfactory bulb’ and the ‘caudate nucleus’. The olfactory bulb – a part of the brain used to analyse smells - responded just as strongly to all of the smells. But the story was different in the caudate nucleus, a part of the brain that responds to positive experiences. Only one smell activated this region: the familiar human. So it looks like you don’t need to wear deodorant to keep your dog happy.