Horse Brain, Human Brain. Janet Jones
Читать онлайн книгу.
horses better able to survive and reproduce in the new conditions. The bones in equine legs became longer. The “knee” (or carpus) on a horse today is actually the equivalent of a human wrist. Everything below that carpus is the equivalent of a human hand with very long fingers. The horse’s ankle or fetlock corresponds to the large knuckles of your hand, where the fingers begin to protrude. With all this lengthening of equine bone came longer tendons. Today’s equine legs are lightning fast for running away, but length makes them fragile too. Long legs also lifted the horse’s head above the level of tall plains grasses—the better to notice predators lying in wait.
Brains Run the Show
With all of these evolutionary changes in the horse’s body, the brain’s sensory organs had to adapt. Peripheral motion vision and precise hearing tuned up so that important sights or sounds—the rustle of a predator’s movement through grass, for instance—would be noticed instantly. Smell became critical for safety from predators and navigation to water. Motor coordination and fast-twitch muscles became vital for escape. These increases in sensitivity were built partly into the eyes, ears, nose, and muscles. But they are even more apparent in the brain tissue where sensory signals arrive for interpretation and in the hard wiring that carries action commands to various destinations in the brain.
The internal operation of brain cells adapted too. Fatty tissue was produced to surround the long tail (or axon) of each neuron, so it could transmit information faster. (Neurons are a type of brain cell that transmit functional information.) In today’s horse, some axons are 10 feet long, stretching from the brain and looping around through the body. The fastest can transmit messages up to 394 feet per second. That’s nearly 250 miles an hour! Glial (“GLEE-ull”) cells—the brain’s janitors—multiplied to keep neurons healthy. The neural ability to form connections became faster and more efficient (fig. 2.1). So did the brain’s ability to kill off unused connections that would only interfere with the learning process.
2.1 Neurons transmit electrical impulses through equine and human brains. The dendrites of one neuron send electricity through its axon. Axon terminals then transmit that information to the dendrites of the next cell.
The brain adapted to collect glucose from food more efficiently, because brains hog glucose for fuel. The human brain represents 2% of your total body weight but uses 20% of your body’s glucose. Equine brains are downright gluttonous—they comprise only two-tenths of a percent of the horse’s total body weight but use 25% of the glucose. Too much glucose can harm our bodies—both equine and human—but too little harms our brains. That’s why we get confused when our blood sugar is too low.
Hard-Wiring for Safety
When dangerous sensory signals were detected on the prairie, a horse couldn’t twiddle his hooves deciding what to do. He had to run first and be alive to ask questions later. To manage that requirement, the equine brain evolved to connect perception directly to action. A nerve signal comes from the eye to the visual processing area of the brain, for example, and the equine brain instantly sends that signal to the motor control area with the command to RUN (fig. 2.2 A). These processing areas are in the surface, or cortex, of the brain. It all happens unconsciously.
2.2 A The horse’s brain detects sights at the visual cortex, then sends the new information to the motor cortex for immediate action.
2.2 B The human brain also detects sights at the visual cortex. But it sends that information to the prefrontal cortex for analysis and evaluation before the motor cortex springs into action.
The wiring between perception and action in the human brain is quite different. A nerve signal comes from our eyes to the visual cortex at the back of our brain, and is usually diverted to a slow path that meanders over to the prefrontal cortex just behind our forehead. There, an unconscious analysis is undertaken: “What have I seen? Have I seen that before? What does it mean? What should I do? Which option is best? Why? Did I have lunch yet? Oh…whoops, let’s pay attention… Hmm, option 17c has worked in the past. Let’s try that one again.” Finally, action kicks in—long after a lion would have punctured an equine throat and gobbled half a leg (fig. 2.2 B).
Innate Instincts
The process of natural selection over millions of years forms the hard wiring of a brain—its major pathways and structures. Evolution always lags behind the present day. So the human brain still functions according to its ability to hunt meat and gather berries, keep its body warm and dry, find mates in the savannah, and try to prevent the children from being eaten by lions. It doesn’t matter that today we drive to the grocery store instead of spearing a wildebeest for dinner, meet potential mates online, and try to prevent the children from being shot in their schools.
Some pathways make stops here and there along the route to their brain destinations—and often, these stops occur at places where the path ended a few million years ago. When scientists see an abandoned way station like that, we have evidence that the brain used to work differently than it does now. For instance, in 2018 researchers found links in the human brain between areas for navigation and smell. People no longer need to smell their way to water, but at one time that ability was so critical for survival that our brain structures changed physically to account for it.
Most psychologists agree that the initial stages of romantic attraction are hard-wired. You don’t turn the process on, and you can’t just flip a switch to turn it off. The feelings are involuntary. But that doesn’t mean we have no recourse. We can work around attraction by learning to notice and identify it, pausing to think carefully about its implications, listening to Mr. or Ms. Perfect’s point of view, and removing ourselves from awkward situations. The feelings are still there, but we don’t have to act on them.
Shying is a good example of hard-wired behavior in horses. Equine brains evolved to whirl and bolt when potential danger occurs. Horses are captive to the naturally selected aspects of their brains, just as we are to ours. In addition, horses have far less ability to manage their hard-wired behavior than humans do. They’re super-smart but do not have the prefrontal cortex to control their instincts fully. We cannot expect a horse to smell a bear a few feet away and simply walk on.
This, by the way, is not a hypothetical example. Aspen, a furry dun pony belonging to a friend, tended to shy out in the back forty. One area near a thicket of willows was especially difficult for her to negotiate. She was convinced of danger there, tightening her muscles, doing the quickstep as if on Dancing with the Stars, and opening her eyes wider every time she approached. In frustration, her owner hired a trainer to get Aspen past this foolishness.
The trainer hopped on one fall day and rode Aspen to the thicket, where she pulled her usual shenanigans. He insisted she move closer to the bushes and, trembling, she eventually agreed. Just about then, a black bear bounded out of his cover, moving on all fours straight toward Aspen—who took off hell bent for election. Everyone learned some lessons: Sometimes it really is best to listen to the horse. And don’t poke the bear!
So do we have to allow every horse to spin out from under us whenever a leaf wiggles? Of course not. We can teach the horse to get to know a frightening area over time, to shy with smaller movements, to slow down and investigate after shying, to trust our leadership. We can teach ourselves to distinguish between equine nerves and true fear. We can overcome our frustration—after all, the horse is behaving in a perfectly natural way. Horses shy just like car passengers slam their useless brake feet into the floorboards and gasp for air when expecting a crash. It’s the brain’s involuntary method of staying alive.
Social Dynamics
Because of their distant past, horses are strongly social animals with herd instincts. They respond to their buddies at all times. We humans fail to notice much of this subtle interaction, and it weakens when we are around. But left on their own, horses rely on group perception, learn by imitation, seek leadership