In humans, the forebrain expanded to form cortical hemispheres whose language and thought abilities set us apart from other species. The hindbrain cerebellum packs about 80% of the brain’s nerves into 10% of its volume, but forebrain nerves occupy about 75% of its volume because they are larger and need more support cells. The cortex is a 2-5mm thick folded sheet with six layers while the midbrain hippocampus only has three layers. It was the last part of the brain to evolve and is the last to mature in children but if other parts ran the feedback loop before it, how can it direct behavior? The answer, it seems, is with difficulty.
By studying children Piaget concluded that thought and language develop in four stages:
1. Sensorimotor (0 to 2): Babies and toddlers think in sensorimotor terms.
2. Preoperational (2 to 7): Children begin to think symbolically and learn language.
3. Concrete operations (7 to 11): Children think logically about concrete events.
4. Formal operations (12+): Abstract thought emerges.
These stages suggest that the human ability to think matures as the brain does, which by its evolution was first the hindbrain, then the midbrain, and finally the forebrain cortex.
In the sensorimotor stage (0-2), the hindbrain directs activities like reaching and standing, so it also tries to speak as those around it do. The result is infant babbling, which can sound like speech but is actually just the copying of sounds with no attached meaning. Even so, it lets an infant learn all the phonemes of its language, including intonations, before it learns its first word at about one. At this point, the midbrain can’t lay down memories, so before two years or later we have childhood amnesia, a period we can’t remember because there are no long-term memories, and animals are the same (Feigley & Spear, 1970).
In the preoperational stage (2-7), the midbrain matures enough to associate sounds with sensations, to give them meaning. At the same time, the child learns syntax, the rules of word order in sentences, possibly using the hindbrain. Yet it still thinks emotionally, that everyone sees the world as it does. For example, a five-year-old shown a chocolate box will say it contains chocolates, but if it is shown to contain pencils, and is asked what another child will think is in the box, they say pencils not chocolates, so they can’t project how others see the world yet.
The first speech is then egocentric, as the child keeps up a running commentary on what they do, even when alone. At first, they comment after an action, so a four-year-old may stroke a teddy bear then say “Good boy”, but at five the same child says “Good boy” as they stroke it, and at six they say “Good boy” then stroke it. It is as if part of the brain first observes what happens after-the-fact, then makes current comments, and finally predicts what will happen, so:
“One area of the brain and mind may initiate a behavior, which is witnessed or experienced by other (disconnected) brain areas, only as it occurs outside the brain and body.” (Joseph, 2017a), p442.
Cortical language is then initially an observer rather than a player, so it comments on what the body does but can’t change it.
In the concrete operations stage (7-11), the midbrain still dominates, so behaviors change by reward and punishment not logic, but the cortex learns to apply concepts like number to concrete things. For example, given two equal length lines of checkers, spacing one line more makes it look bigger, so a child under 7 may say it has more checkers, but by 9 they know that number doesn’t depend on size (Figure 6.30). They can apply concepts like number to concrete images but can’t connect one abstraction to another.
Only in the formal operations stage at about twelve can the child connect abstract concepts, to see speed for example as distance divided by time. In effect, the forebrain intellect matures enough to allow genuine thought. Prior to this, children can rote learn history dates by repetition, or associate concrete sensations like similar faces, and even recall entire textbook pages, but still struggle with abstract mathematics. For example, consider the following problem:
Bob rides his bicycle to pick up his motorbike from the repair shop at 10 mph. How fast must he ride his motorbike back to average 20 mph for the whole trip?
Emotional thinking based on associations suggests 30mph as 30 plus 10 averages 20, but this isn’t right. To see this, if the shop is 10 miles away, at 10mph it takes an hour to get there, so he must instantly return to average 20mph! The answer then is that it’s impossible because doubling a distance only doubles the speed if time doesn’t change for the return journey, which is impossible. Problems like this are hard because speed as distance over time is an abstract ratio that only the forebrain intellect can handle. A child can’t understand the dx/dt ratios of calculus until their intellect matures, so training a six-year-old in calculus has little effect because midbrain learning isn’t forebrain learning.
If the above example was a struggle don’t worry about it, as real thought always is. The brain must change its locus of control from hind/midbrain rote or associative thinking to intellectual thought, to work in a new way. Even after twelve the cortex still needs another decade to learn to think formally and it continues to mature into the mid-twenties. The forebrain then changes its role, from backward thinking to justify existing knowledge, to forward thinking to discover new knowledge. Cherry-picking the Internet to find facts that confirm preconceptions is then backward thinking, while impartially using facts to form conclusions is forward thinking, which underlies the scientific method. Western science traces back to Socrates, who essentially invented forward thinking, but two thousand years later we still struggle to follow his example because thought hurts.
Does the forebrain control the feedback loop as it matures? It has the links to do so as the frontal-lobe motor cortex (Figure 6.31) projects nerves to body muscles based on their importance (Figure 6.32). A voluntary act like raising a hand is accompanied by motor cortex activity, and supplementary and pre-motor areas light up before that to prepare the action. They activate even at the thought of moving so experiments can predict an action long before the muscles move (Nachev et al., 2008). Are the frontal lobes then the long-sought senior executive of the brain? If so:
“… the “will” to move begins in the SMA and medial frontal lobes and exerts executive control over the secondary, primary and subcortical motor areas which then perform these “willed” actions.” (Joseph, 2017b), p151.
Motor cortex damage should then produce paralysis but rats with no motor cortex still move normally but struggle with unexpected events, so it is required to learn a motor skill but not to execute it (Kawai & et al., 2015). Even with no cortex at all, rats, cats, and dogs can run a treadmill and monkeys can peel a banana, so what does the motor cortex do? The current view is that it evolved to handle unexpected events like a slip or fall, which requires a rich analysis of sense input that only the cortex can provide (Lopes & et al., 2023). The motor cortex role is then to increase flexibility, also called robust dexterity (Petryński, 2005), as system performance depends on surviving external as well as internal changes.
The picture that emerges from neuroscience is that multiple systems drive bodily actions:
“Figuratively speaking, the skeletomotor output system is akin to a single steering wheel that is controlled by multiple drivers …” (Morsella et al., 2016), p6.
The body is then like a car with three drivers, except that each has their own dedicated steering wheel and controls, map of the outside world, and memory of past events. But if a car with three drivers meets an obstacle, what stops one driver turning left as another turns right, so they cancel and crash into it? How can three brain control centers effectively share control of the same body?