What makes a dog brain different from a human brain?

March 2021

Answered by: Luiza Volpi, PhD Candidate in Neuroscience

A dog’s brain is anatomically quite different than a human’s brain. The relative sizes of different brain regions also vary when compared to the human brain. This gives us interesting clues about how the dog’s brain may work differently than ours, because different brain areas are generally associated with different functions. To explore how the world looks from your dog’s point of view, I will focus on the senses, specifically on sight—because it’s our strongest sense, the one we rely on the most, and smell—which is our furry friend’s sharpest sense.

More than half of the human cortex¹—the part of the brain involved in high-order functions, such as thought, perception and memory—is dedicated to vision. To exemplify how important vision is to us, most of us “see” the world in our mind’s eye when we read a novel, and we seem to enjoy it more when we do so². When we study other animals, our experiments are often based on how we experience the world, which may undermine how the animals we are studying might do so. A quite famous example is the ‘mirror test’ for self-awareness developed by Gordon Gallup Jr. in 1970³. In this test, we paint a spot on someone’s head and make them look at a mirror. If they are aware that the mirror image is their own reflection, they will try to clean out the smudge. Several animals, including elephants and monkeys successfully ‘pass’ the test^4,5, but others such as dogs seem to fail it. However, in an adaptation of the test, urine samples of multiple dogs were presented to one dog, including their own. The dog spent a lot more time smelling the other dogs’ urines than its own⁶, indicating that dogs do recognize who they are—just not in the same way we do. I wonder whether people would be able to recognize themselves by the smell of their own pee!

Dogs have a significantly larger area in the brain for processing smells—proportionally around 40 times larger than ours. They also have a significantly larger area of olfactory epithelium (smell- sensitive tissue inside their noses), with 30% more olfactory receptors⁷ than us. Olfactory receptors are specialized cells that detect odorant molecules, and relay this information to the brain, giving rise to the sense of smell. Dogs are sensitive to a larger variety of odorants, are more efficient in discriminating between them, and can detect them even in very low quantities⁷. So, when we train our dogs to rely on visual cues, e.g., by pointing down so they sit, we are disregarding their strong suit.

Although our vision is better than the dog’s, we also tend to underestimate theirs. A common misconception is that the dog sees the world in black-and-white. Color vision requires special light-detecting cells located in the retina called cones. Dogs have two different types of cones, one that responds preferentially to green light and the other to blue light¹. Most humans possess three types of cones—for blue, red, and green light. Thus, dogs see the world in shades of blue and green—much like a red-green colorblind person—and unlike us are unable to distinguish red from green. However, dogs seem to have better vision for flickering and dim light, but worse sharpness of vision and depth perception⁸. Even so, dogs are pretty much sensitive to the same visual objects that are most important to us—like looking at and recognizing other people. At the level of visual processing in the brain, just like us, dogs have very specialized visual areas dedicated to animate beings, such as other dogs and people^9,10. In the end, we are not so different after all.

References

1. Snowden, R., Thompson, P. & Troscianko, T. Basic Vision: An introduction to visual perception. (Oxford University Press, 2012).

2. Weibel, D., Wissmath, B. & Mast, F. W. Influence of Mental Imagery on Spatial Presence and Enjoyment Assessed in Different Types of Media. Cyberpsychology, Behav. Soc. Netw. 14, 607–612 (2011).

3. Gallup, G. G. Chimpanzees: Self-Recognition. Science (80-. ). 167, 86–87 (1970).

4. Plotnik, J. M., De Waal, F. B. M. & Reiss, D. Self-recognition in an Asian elephant. PNAS 106, 17053–17057 (2006).

5. Toda, K. & Platt, M. L. Animal cognition: Monkeys pass the mirror test. Current Biology 25, R64–R66 (2015).

6. Cazzolla Gatti, R. Self-consciousness: beyond the looking-glass and what dogs found there. Ethol. Ecol. Evol. 28, 232–240 (2016).

7. Jenkins, E. K., DeChant, M. T. & Perry, E. B. When the nose doesn’t know: Canine olfactory function associated with health, management, and potential links to microbiota. Frontiers in Veterinary Science 5, (2018).

8. Miller, P. E. & Murphy, C. J. Vision in dogs. Journal-American Vet. Med. Assoc. 207, 1623–1634 (1995).

9. Bunford, N. et al. Comparative Brain Imaging Reveals Analogous and Divergent Patterns of Species and Face Sensitivity in Humans and Dogs. J. Neurosci. 40, 8396–8408 (2020).

10. Thompkins, A. M. et al. Separate brain areas for processing human and dog faces as revealed by awake fMRI in dogs (Canis familiaris). Learn. Behav. 46, 561–573 (2018).