We like to control things, so our computer networks were centrally controlled until it was discovered that decentralized networks like Ethernet are ten times faster, and degrade gracefully under load instead of crashing suddenly. When the Internet began, pundits expected it to collapse in chaos without central control, but it didn’t because decentralization allowed it to survive.
Early brain theories also expected central control, like Schacter’s model (Figure 6.3), where an executive system directs responses after a conscious awareness system receives sense data, memory, and thought (Schacter, 1989). The cerebral cortex, the outer layer of the brain (Figure 6.4) that handles thought and language, was then expected to contain the executive unit.
However the cortex, the most advanced part of the brain, consists of two hemispheres that split the work between them. The left hemisphere controls the right side of the body and the right directs the left, so which is the executive?
One hemisphere was expected to dominate the other by the 800 million nerve bridge that connects them, called the corpus callosum (Figure 6.5). But then surgeons treating epilepsy, an electrical disturbance that spreads between the hemispheres, cut the corpus callosum to stop that, as cutting it in animals didn’t seem to harm them. The treatment worked, but while serious side-effects were expected, the patients spoke and acted normally, so the corpus callosum wasn’t letting one hemisphere dominate the other.
To investigate further, researchers devised what became known as a split-brain experiment. Brain nerves showed that the hemispheres divide not only body control but also vision, as the left hemisphere receives nerves from the right side of both eyes while the right receives nerves from the left side (Figure 6.6). Each hemisphere then controls not only the opposite side of the body but also of the visual field. That the left hemisphere handles the right visual field and the right hand, and the right hemisphere handles the left visual field and left hand, allowed the split-brain experiment shown in Figure 6.7 as follows.
Subjects were shown a set of pictures and asked to point to the one that matched what they saw on a 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 but 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 both seemed unaware 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.
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 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.
The results suggested that the hemisphere that controls language is 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). It follows that neither the left hemisphere nor the right hemisphere is the brain’s executive, but how then do we consciously experience one visual field when the corpus callosum is connected?
We assume the left hemisphere is conscious thanks to language, but is the right hemisphere the same? It doesn’t control speech 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. 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, in one case 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. Banging a nail through a mother-board stops it working but brains aren’t that fragile, so the inventor of our computers wondered:
“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 decentralized control to survive so if one hemisphere fails, the other carries on as best it can. If the body is a ship, the brain crew that runs it then 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 sense input we respond to, so why not peel away the brain layers to find the observer? Searching the Internet for its center reveals none and neuro-science is clear that the brain is the same, so it can’t explain why we experience a single self:
“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 given two contradictory facts, science doesn’t cherry-pick one to explain away the other but tries to reconcile them. How a decentralized brain can produce a unified consciousness is addressed later (6.3) but for now, the conclusion is that our brains are decentralized because evolution required it.