Dogs have long established themselves as a valuable component of human civilization. In addition to being our loyal companions, a human's best friend has many ‘nose talents’, making them employable in diverse settings, from drug detection at the airport to insulin retrieval at home. Breeds such as German shepherds and beagles have a reputation for excelling at such tasks, raising the question of whether some dog varieties have evolved more advanced smell systems than others. However, recent research suggests that smell genes are mostly conserved across dog breeds. To better understand how dogs’ brains are wired to efficiently process smells and how these neuronal connections may vary across individuals, Asami Nakaimuki and colleagues from Eötvös Loránd University in Budapest, Hungary, analyzed brain scans from 33 dogs (Canis familiaris) of diverse breeds and ages.
In a previous study, pet dogs had been trained to lay down and stay still to get their brains scanned (without been sedated or restricted), producing the scan images analyzed by Nakaimuki and colleagues in the current study. Using image processing software, the researchers looked at specific regions of the brain known to play a role in smell detection. Within these brain areas, they found 26 functional connections, with the strongest neuronal communication taking place between the left and right side of the smell-related parts of the brain, as opposed to within a specific area of either one. This suggests that, during scent detection, dogs rely heavily on the communication traffic between the two brain hemispheres to decide what an odor means and how to act upon sensing it.
Next, the researchers wondered whether age, sex or skull shape would explain differences in smell capabilities among dogs. While they found no differences between males and females, they realized a trend where aging decreases the strength of the brain connections associated with smell, suggesting that an older dog's sense of smell might not be as strong as it once was. The researchers also inquired about the influence of head shape in brain connectivity. Here, they found that dogs with an elongated skull had stronger, more elaborate networks connecting smell brain regions than dogs with a more rounded head, suggesting that the dogs with more pointed heads have a stronger sense of smell than rounder headed breeds. However, it is worth noting that many small-headed breeds were missing from the current study, so a more comprehensive comparison would be needed to fully understand the relationship between skull shape and smell processing in the brain.
In all animals, specialized brain regions form distinctive networks to communicate with each other, and uncovering what those specific connections look like can reveal critical cues for how the brain works. We now know that dogs have a well-defined network of brain regions dedicated to smell interpretation, which does not change significantly between good boys and good girls but may deteriorate with age. This study also suggests that certain head shapes may not provide enough room for the strong neuronal connections that a dog needs to become a top crime sniffing investigator, although given the radically diverse breed repertoire that exists, more research is warranted to fully understand the matter. And as far as Fido goes? He's just waiting for all the treats he was promised in exchange for his contributions to this work.
