The human brain doesn’t have an instruction manual but if it did, it would say that many ways to control the feedback loop is a feature not a bug. Brains have to process sense input, body state and muscle output anyway, so evolving all three was better for survival than one (Figure 6.32). If the brain had only one control center, it would be the hindbrain that evolved first not the cortex that came last, so we wouldn’t be here. The ideal for brains like ours is to use the best brain control center for the job.
Figure 6.32 oversimplifies as the forebrain part that receives muscle input is next to the motor nerves for those muscles, like a single gate for input and output. In fish, the cerebellum evolved to run the brain-world feedback loop using information from the still evolving forebrain and midbrain. In birds and mammals, the limbic system became an alternate control center that could override the cerebellum, which still managed fine motor control. Much later, in mammals like us, the neocortex evolved to independence but its control of the emotions is often quite limited.
The result is a brain with not one center of control but three, where each center monitors body and sense input with the neural connections it has and does what it decides is best. Evolution has given us a brain with super-fast movements, powerful bodily emotions and complex thoughts because different situations need all three. This isn’t always easy as the centers can’t “talk” to each other as people do because millions of years of evolution separate them so they all speak different “languages”.
For example, falling on a hard surface is a common cause of injury as it happens so quickly and what the brain does in that fraction of second decides whether we end up in hospital or just get back up. The intellect is too slow to act in time and an emotional center panic isn’t much use, as a violent muscle spasm to avoid falling can injure bones or joints more than the fall itself. In most cases, it is best if the movement center takes over to roll in the fall, as parachutists do.
A person scared of spiders can discuss their fear intellectually and accept that a little non-poisonous spider isn’t a threat. They have all the data needed for a non-fear response, but putting that same little spider on the table still makes them jump up in fear! The emotional center ignored the talk but an actual spider made it press its red danger button. And if during the conversation an object fell from a shelf above, the moving center might make a hand catch it before the intellect even recognizes it. Different brain centers are too busy processing external events to talk internally.
The three-in-one answer that evolved from the early forebrain-midbrain-hindbrain division gives us fast responses, powerful emotions and complex thoughts. The traditional idea of human nature as intellect, emotions and will derives from this early neural division of labor. The three-center approach to brain evolution can be illustrated by a story:
Once upon a time there were three brothers who flew a tiny plane. Elder brother handled the flight controls, middle brother monitored the cockpit knobs and baby brother looked out the window to see what was out there. By delivering goods in the city to earn money, they were eventually able to afford a jet plane for intercity travel that had knobs to automate landing, takeoff and flight among other things. As a result, middle brother was now mainly in charge but elder brother still monitored the controls to make fine adjustments and took over in emergencies. Middle brother had a thrust button for more power but he had to use it at the right time. As little brother grew older, he used what he called ‘symbols’ to record events on bits of paper but the others just used his spotting ability.
Intercity travel made more money, until they could afford an intercontinental jet with state-of-the-art computer control. Elder brother preferred the manual flight controls and middle brother his dials and knobs but younger brother found the computer screen better than paper. It took longer but he could control most of the plane with it and even code messages to other planes. The brothers were too busy to talk in flight, so he would demo a new flight technique by computer control and they picked it up if useful. He even learned how to fly into space but they mostly flew between continents.
Their plane was constantly being upgraded. At first, elder brother used a simple dot radar to avoid colliding with other planes. When a radar with pictures instead of dots was installed, he found it too complex for manual flying but middle brother found it useful to identify friend from foe. When computer radar arrived, the first two found it too complex and slow but little brother used it to analyze trends and causes. Over time, the brother’s plane dominated the airways because three pilots are better than one if each does what they are good at.
The brain has three centers just as cars have different gears for different situations but why do we experience one driver? All that neuroscience knows about the brain, from blindsight to the split-brain, suggests many “I” not one. Our sense of a single “I” suggests that nerve input goes to a center that is also the origin of all motor nerves, but science assures us it isn’t so:
“In contrast to this first-person experience of a unified self, modern neuroscience reveals that each brain has hundreds of parts, each of which has evolved to do specific jobs – some recognize faces, others tell muscles to execute actions, some formulate goals and plans, and yet others store memories for later integration with sensory input and subsequent action.” (Nunez, 2016) p55.
Neuroscience calls the issue of how different brain areas work together the binding problem.