By Sophie A. Barton and Erin E. Hecht

Dogs are extraordinarily diverse – they come in all shapes, sizes, and colors. This is largely the result of strong artificial selective pressures that humans have exerted on dogs in recent centuries. But is this variation only skin deep? Judge for yourself in the picture of dog brains below!

The Canine Brains Project studies how humans have shaped the structure, function, and behavioral output of the dog brain. Usually we’re focused on how artificial selection on dog behavior might alter brain organization. But given that there has also been strong selection on head shape, we wanted to know if this might influence brain anatomy as well.

In our recent paper “Covariation of skull and brain morphology in domestic dogs”, we investigated how regional gray matter volume varies with the dimensions of the neurocranium, which houses the brain. We did this with an opportunistically-acquired dataset of T2-weighted structural MRI images of 79 dogs from the University of Georgia’s Veterinary Teaching Hospital. All of the scans used for the study were screened by a neurologist and deemed not to have any gross structural abnormalities. To analyze the data, we used voxel-based morphometry, which is a data-driven method for assessing variation in regional tissue volume across the entire brain.

We found dogs with shorter and wider heads had significant reductions in the volume of gray matter of several regions, including the right olfactory bulb and cerebellum. But dogs with narrower and longer heads had more widespread reductions in temporal cortex, sensorimotor cortex, occipital cortex, amygdala, hippocampus, hypothalamus, and brainstem.

Sagittal images of dog brains with different skull shapes (left). Reduced regions of gray matter volume in extreme brachycephalic in blue and dolichocephalic head shapes in green (right).

While we were unable to examine behavioral correlates of the regional gray matter reductions observed in this study, previous research has found behavioral differences between dogs of different head shapes. For example, dogs with shorter and wider heads excel at establishing and maintaining eye contact with humans, whereas dogs with longer and narrower heads are more likely to chase small animals. Future research should explore if the brain volume reductions observed in this study have any direct behavioral consequences.

Sophie Barton is a PhD candidate in the Hecht Lab of the Department of Human Evolutionary Biology.

Erin Hecht is an assistant professor of human evolutionary biology at Harvard University.

Learn more in the original research article:
Covariation of Skull and Brain Morphology in Domestic Dogs
Barton SA, Kent M, Hecht EE.  J Comp Neurol. 2024 Sep;532(9):e25668. doi: 10.1002/cne.25668. PMID: 39268838.