Our computer networks were centrally controlled until we discovered that decentralized networks like Ethernet are ten times faster, and degrade gracefully under load instead of crashing suddenly. Yet when the Internet was first proposed, pundits still expected it to collapse in chaos without central control but it didn’t, because decentralization allowed it to survive.
Likewise, early brain theories still expected central control, like Schacter’s model (Figure 6.3) where a central executive inputs conscious awareness of sense data, memory, and thought to respond (Schacter, 1989). It was then assumed that the cerebral cortex, the folded outer layer of the brain (Figure 6.4) that handles thought and language, contained the executive unit.
Yet the cortex, the most advanced part of the brain, is divided into hemispheres that share the work between them. The left hemisphere controls the right side of the body and the right directs the left, but which then is the executive?
One hemisphere was assumed to dominate the other via the corpus callosum, the 800 million nerve bridge that connects them (Figure 6.5). But then surgeons treating epilepsy, an electrical malfunction that spreads from one hemisphere to the other, tried cutting the corpus callosum as doing this in animals didn’t seem to harm them. The treatment worked, but while serious side-effects were expected, the patients seemed to speak and act normally, so some even wondered if the corpus callosum was just a structural support!
To investigate further, researchers devised the split-brain experiment. They knew that the left hemisphere controls the right side of the body and the right controls the left, and for vision, the left hemisphere receives nerves from the right side of both eyes while the right receives from the left side (Figure 6.6). Hence, the left hemisphere processes the right visual field and controls the right hand, while the right hemisphere processes the left visual field and controls the left hand.
The split-brain experiment shown in Figure 6.7 then worked as follows.
Subjects were asked to point to the picture that matched what they saw on the screen, which unknown to them was split into two pictures. The result was that if the left of the screen showed snow and the right showed a claw, the left hand chose a shovel to match the snow, and the right chose a chicken to match the claw! Subjects asked what they saw just said a claw, because the left hemisphere that controls speech only saw that. With the corpus callosum cut, each hemisphere acted like a brain in itself, and neither seemed aware of the other’s choice, so there was no conflict. Rather than one hemisphere dominating the other, both just analyzed their visual data and responded, so no central executive was needed.
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If a subject was specifically asked why his left hand chose a shovel, the reply might be “you need a shovel to clean up after chickens”. Yet researchers knew that the verbal left hemisphere didn’t know why the shovel was chosen because it didn’t see the snow, so it invented a reason! They concluded that it was just trying to explain events as best it could:
“These findings all suggest that the interpretive mechanism of the left hemisphere is always hard at work, seeking the meaning of events. It is constantly looking for order and reason, even when there is none – which leads it continually to make mistakes. It tends to overgeneralize, frequently constructing a potential past as opposed to a true one.” (Gazzaniga, 2002), p30.
In interpreter theory, the left hemisphere’s language and thought are more servant than master, so if the brain is a federation of agents (Minsky, 1986), it is like a diplomat whose job is to explain the decisions of others, not the CEO as some suggest (Kaku, 2014). Given that the animal most likely to harm a human is another human, perhaps our intellect grew as our societies did because those who can justify their actions survive. Science then, probably isn’t what our intellect originally evolved to do.
But is the right hemisphere really conscious if it can’t speak? It doesn’t specialize in language but that doesn’t make it illiterate. In one study, a split-brain boy was asked “Who is your favorite?” but the left of the screen showed “Who is your favorite girlfriend?” (Wolman, 2012). There was no verbal reply, as the left hemisphere didn’t see the word girlfriend, but a nervous giggle revealed that his right hemisphere understood fully what it saw. The boy was then able to use his left hand to select scrabble tiles to spell out L-I-Z, a cute girl in his class. It followed that the right hemisphere could read and spell, so it was conscious in any way you care to define it:
“Everything we have seen indicates that that the surgery has left these people with two separate minds, that is, two separate spheres of consciousness. What is experienced in the right hemisphere seems to lie entirely outside the realm of awareness of the left hemisphere. This mental division has been demonstrated in regard to perception, volition, learning and memory.” (Sperry, 1966), p299.
This discovery, that dividing our brains at the highest level produces in effect two people, was surprising. Yet in evolutionary terms, it favors survival, because if one hemisphere is damaged, the other can carry on. For example, take the case where an iron rod pierced the middle and left cortical lobes (Figure 6.8) of a railway worker called Phineas Gage, who soon after walked off, conscious and speaking. He showed disturbed behavior but lived for 13 more years and died of unknown causes. If you bang a nail through a mother-board, it stops working, but brains aren’t that fragile, as Von Neumann observed:
“How could a mechanism composed of some ten billion unreliable components function reliably while computers with ten thousand components regularly fail?” (von Neumann, 1948).
The answer is that the brain duplicated functions and decentralized control to survive, so if the body is a ship, the brain crew that runs it has no captain, even at the highest level:
“Studies of the structural and functional organization of the brain have shown that this organ is, to a large extent, decentralized, and processes information in parallel in countless sensory and motor subsystems. In short, there is no single homunculus in our brains that controls and manages all these distributed processes.” (Singer, 2007).
We experience the world as observed sense input that we respond to, so why not peel away the brain layers to find the observer? Unfortunately, doing this is like searching the Internet for a center that it doesn’t have. Neuroscience is clear, that the brain is a decentralized collective with no center:
“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.
There are then two facts, that we experience one observer, and that our brain is a decentralized collective with no central processing unit (CPU). Some conclude that a brain with no center can’t experience one, so conscious states must be delusions (Dennett, 1991), but delusions vary while our experience of being one observer runs across all cultures. Given two contradictory facts, science doesn’t cherry-pick one and explain away the other but tries to reconcile them. The question of how decentralized brains produce a unified consciousness is addressed later (6.3) but for now, the conclusion is that brains are decentralized because evolution required it, so what else did it require?