The Master Betrayed

Two Ways of Being

Split-brain studies expose the difference between the map and the terrain.

Misconceptions

As explored in previous episodes, the two hemispheres of our brain have distinct roles to play, each contributing to the whole of human behaviour. The study of these two realms, however, has resulted in a simplification and misconception of the findings, namely that the right hemisphere is just “touchy feely” and not very reliable - creative but incapable of hard thinking - whereas the left hemisphere is rational and utilises language, and is responsible for the serious work of the brain.

Split brain patients

McGilchrist explains how these misconceptions came about following the popularisation of some fascinating studies on “split-brain” patients. These patients had undergone an operation that cuts the fibres connecting the two hemispheres, in order to minimise the impact of intractable epilepsy. Disconnecting the hemispheres meant that when an electrical excitation (causing an epileptic seizure) started in one hemisphere, it could no longer spread to the other, allowing the patient to retain consciousness and use of that hemisphere.

As an interesting aside, these patients did not see a huge change in themselves post-operation. There was some initial disorientation or conflicting desires, for example, a patient might reach for a book to read or their partner to kiss with one hand, and push them away with the other, but after a few months this had settled down.

Experiments have also been carried out on patients who have had one brain hemisphere temporarily shocked, either by Electroconvulsive Therapy (ECT - a treatment for depression) applied to one hemisphere or another, or by transcranial magnetic stimulation, in which a magnetic field can temporarily repress activity in one hemisphere.

To draw a flower

Once one hemisphere has been repressed, it is possible to carry out experiments on patients that explore how each hemisphere interprets the world. McGilchrist shares the example of drawing based experiments carried out by Russian scientist Nikolaenko, in which patients were asked to draw a flower. When the left hemisphere is disabled and only the right is active, the patient will draw a recognisable flower in its entirety, “the whole living, flowing shape of the flower”. In contrast, when the left hemisphere is active and the right is not, the patient will draw the flower as something that looks like a button, “entirely geometrical, symmetrical, stereotyped`”. Similarly, when asked to draw a person, the left hemisphere will create simplified images of rhomboids and stick people. In other words, the left hemisphere is incapable of seeing spatial depth, and as such the drawings created are all flattened, without a sense of perspective, and a much reduced representation of the thing is depicted. As McGilchrist states, “the left hemisphere offers a map where the right hemisphere offers us a view of the terrain, because the terrain is where we live”.

Map vs Terrain

A further experiment into the two hemispheres that illuminates this distinction that can be drawn between the hemispheres is one carried out into syllogisms by Degelin and Kinsbourne. A syllogism is a couple of propositions that if true lead to a conclusion. The classic example is: all men are mortal, Socrates is a man, therefore Socrates is mortal. Patients were presented with a syllogism and had to decide whether it was true or false, the catch being that one of the premises given was intentionally false. So for example, all monkeys climb trees (true), the porcupine is a monkey (false), therefore the porcupine climbs trees (false).

Patients were asked to determine, given these premises, whether the conclusion is true. With both hemispheres functioning, the individual will answer ‘no’ and state that porcupines do not climb trees, since a porcupine is not a monkey, and so the conclusion does not follow (some porcupines do in fact climb trees, but the researchers and patients did not know this at the time). Similarly, with just the right hemisphere active the same conclusion is reached. However, when just the left hemisphere is at play, the patient will answer ‘yes’ and claim that the conclusion is correct and porcupines do climb trees. When pressed by the examiner, the patient will admit that they know a porcupine is not a monkey, however they will simultaneously insist that a porcupine must be a monkey, due to the logic of the syllogism, and therefore must climb trees. Those with just the left hemisphere active are more interested in the internal consistency of an entirely theoretical construct than the reality of their lived experience. The left hemisphere decides that if it follows the logic, it is true, whereas the right hemisphere and a fully intact person will balance the information given to them with judgements based on their experience. They move beyond the map to the terrain.

Computer says no

McGilchrist sees the dominance of a left hemisphere way of thinking in contemporary life, encapsulated by the Little Britain sketch of “computer says no”.

“My take on it is that we are we are taking this attitude more and more towards reality, that if the box is ticked, then it happened. And if the box is not ticked, it didn't. If it fits into the category, it's real. If it doesn't fit into the category, it's just not real because the computer can't compute.”

He shares an unbelievable story of a woman who is called to the hospital with the news that her brother died in an accident. When she goes to see him in the morgue she is shocked to find that his body is still warm, and she believes she can feel a very faint pulse. The nurse reassures her he must be dead as that is what the form she is holding tells her: “Now don't you worry about that, dear. It says quite clearly on this piece of paper that he's dead.” The woman disregards the nurse and rushes out into the corridor, where she finds a passing medic who administers intracardiac adrenaline, saving the brother’s life.