A new brain imaging study from the ELTE NAP Canine Brain Research group has revealed that age and brain shape affect how strongly olfactory brain regions are connected. The researchers used resting-state fMRI on awake dogs to map olfactory functional connectivity. Published in Scientific Reports, this study marks the first exploration of this network in dogs and how it relates to individual characteristics.
Humans have long depended on dogs' sense of smell, but we know surprisingly little about how dogs' brains support it. "Many behavioral studies have shown that individual differences influence how much good sniffers dogs are," says lead author Asami Nakaimuki, PhD student at the Department of Ethology, ELTE Eötvös Loránd University, "but we do not know if individual differences are also reflected in the brain network."
The researchers first described a functional connectivity network across olfactory brain regions, using a special technique called resting-state fMRI, in which dogs did not do anything, just lay still for 8 minutes. The network partially corresponded with the previously reported anatomical connectivity. Their results showed that younger dogs and those with more elongated brains had stronger functional connectivities in olfactory regions than older dogs and those with rounder-shaped brains. There were no differences between males and females. "This matches previous findings from behavioral research," explains senior author Attila Andics, co-PI of the ELTE NAP Canine Brain Research Group. "Just like humans, dogs' smell sensitivity fades with age. Our results also support claims that long-headed dogs perform better in smell tests."
Interestingly, the team also found particularly strong communication between the left and right sides of the same olfactory brain regions – a pattern seen in rodents and even in people born without a sense of smell. "This might be the default setting in the mammalian brain," says Nakaimuki.
"Dogs are famous for their good noses, and now we know that the length of the nose, and relatedly, the shape of the brain also matters," summarizes Enikő Kubinyi, head of the Department of Ethology at Eötvös Loránd University. "Nose length affects not only the size of the olfactory epithelium but also the shape of the brain and the communication between brain regions involved in the sense of smell. The next step is to examine what happens to these networks when the dog's nose is put to work—that is, when it encounters a scent."
