Prefrontal Cortex in Horses and Humans

Source: Schmidt, M.J. Knemeyer, C., & Heinsen, H. (2019). "Neuroanatomy of the equine brain as revealed by high-field (3Tesla) Magnetic Resonance Imaging

Many horse owners think the existence of the prefrontal cortex is a major controversy in equine science. It’s not. It’s just an area that’s riddled with misinformation. Curiously, most people—horsey or not—want the prefrontal cortex to be part of the horse’s brain. How does their reasoning go? “If I have one and I’m smart, he must have one because he’s smart.” That’s an oversimplified generalization, but at base, I think it’s true.

The prefrontal cortex is a small portion of brain tissue located at the front of the frontal lobe in human brains, just behind and above our eyes. It’s responsible for what we call the executive function—planning, organizing, deciding, evaluating, and strategizing. It’s also responsible for judging, worrying, and manipulating. Humans rely strongly on the prefrontal cortex. Horses do not.

Thirty-three percent of the average human cortex—the outer layers of the human brain—is prefrontal. That’s a lot! It matches our sense that we spend a lot of time carrying out the activities of executive function. By comparison, about 15 percent of the monkey cortex is prefrontal, and only 5 percent of the cat and dog cortex is prefrontal. These canine and feline predator brains are capable of limited executive function and spend very little time carrying out executive tasks. But they probably can when they need to.

Prey brains are different in many important ways from predators' brains. Horses have no prefrontal cortex. They do not even have a frontal lobe. The accuracy of these facts is verified easily by consulting recent MRI images of the equine brain. In the photograph here, the frontal lobe would be located above and to the left of the spinal cord and brainstem. You can see there is no brain tissue in this area at all.

So if horses have no prefrontal cortex, how do they solve problems? They use their excellent memories and senses. What worked in the past? What action led to positive consequences? Try that!

I once had a horse going into equine surgery, who was not allowed to eat for 12 hours prior to general anesthesia. The equine digestive system operates on frequent food intake, so 12 hours of fasting is a bunch. Cory had every right to be hangry.

When I arrived at the hospital on the morning of the surgery, he was waiting for me at his stall door. He looked at the hay across the hall, then back at me. Hay… Me… Hay… Me. He nuzzled my arm, then pushed it. He touched his empty feed bucket with a hoof, then lowered his nose to the bucket. He walked to the back of his stall, then strode purposefully to its door in the direction of the hay outside. After each try, he stared into my eyes. No luck.

I rarely give horses treats but had done so for a few unusual tricks in the distant past. Cory began his repertoire. He stretched his front legs straight and pushed his shoulders toward the ground, performing a “down dog” while seeking my attention. Nope. He tried it again with more stretch, the best “down dog” I’ve ever seen, even from a human yogi. He popped his lips, a substitute action I had rewarded nearly 10 years prior to counter-condition pawing. He remembered maneuvers that I had long since forgotten.

The moral of the story? Horses do not need a prefrontal cortex because their memories serve them better than ours serve us. Where a human uses the prefrontal cortex to solve a problem, set goals, and plan hypothetical actions, a horse uses memory.

The last thing a prey animal needs to survive is a prefrontal cortex. All that time spent pondering, deciding, and planning is time taken away from fleeing danger. Over 56 million years of evolution, the equine brain has evolved to prevent wasting time. A horse who considers the meaning of a movement in the grasses is a horse who becomes a predator’s dinner.

The lack of the prefrontal cortex in horses is a gift to them and us. It keeps them alive and helps to sharpen their memories. But it allows us to work with animals who live in the moment, who do not—indeed, can not—judge, criticize, worry, or manipulate. What a refreshing experience!