Fall 2022 Cognitive Science-Biology End-Semester Exam Solution: Carnegie Mellon University

The cerebrum makes up a large part of the brain and has two hemispheres. Discuss the role and function of the cerebrum and cerebellum.

Whereas so much of the brain's volume is functionally vague, being allied to intelligence but with no precision, there are portions of the cerebrum which are quite the reverse. Below the cortex, or grey matter, the bulk of the tissue is a white matter the pathways of fibers. Nevertheless, at the base of it all, completely overshadowed in bulk by the great mass of the cerebral hemispheres, there exists some more grey matter.

Part of this tissue is the hypothalamus, a minute portion of the total brain - about, three-hundredth of it - which seems to have a disproportionate share of duties. 'Is there any pie in the vertebrate organization into which the hypothalamus does not dip its finger?" asked a Lancet leader once. This fraction of brain tissue is involved in the body's water metabolism, temperature regulation (and therefore in perspiration and shivering), appetite, thirst, the levels of sugar in the blood, growth, sleeping and waking, in emotions such as anger and pleasure, in the cycles of the reproductive system, and it is also the main center of the autonomic nervous system. Probably it will be found to be invested with yet more bodily authority when research- workers have probed further into its vital lump of grey matter but, considering that it is smaller than a finger joint, the list is already impressive. Naturally, with such a small but all-important organ, minor damage - even the overcrowding presence of a tumor nearby causes drastic alteration to the body's self-regulatory abilities. Similarly, with such a complex list of duties, there is no need to presuppose a tumor to consider the occasional hypothalamus at fault in itself. Compulsive eating, the tendency to eat too often or too long, may merely be the fault of a hypothalamus whose appetite control center is either inadequately strict or faulty in its assessment of need.

Left-sided dominance The fact that the cerebrum is completely divided by the superior longitudinal fissure to form the two separate cerebral hemispheres is highly relevant to bodily control. In effect, this division causes two regions, each capable of administration. Having two such regions of the cerebral cortex incurs the possibility of a disunited command. Messages from one half of the brain can reach the other half, but the human brain obviates the need for such constant cross-reference by having one cerebral hemisphere dominant to the other. The damage to Pasteur's brain, already mentioned, was to his non-dominant half. He could not have suffered such damage to the left-hand and the dominant side of his brain. Should a child receive damage to its left hemisphere before it is too late, some say before six months, the right hemisphere can take its place. Later on, the chain of command is too firmly embedded, and the dominant hemisphere cannot have its higher and more authoritative role taken over by the other inferior half.

Almost always the left hemisphere is the dominant one. It possesses the speech center as well as wielding unspoken p over the right hemisphere. Why the left should be so dictatorial in this fashion is quite unknown. Allied to this ignorance, often unhelpfully so, is the problem of right- and left-handedness. With the left hemisphere controlling the right half of the body, and with the left hemisphere nearly always dominant, these facts might seem to explain the overwhelming majority of right-handers, but alas for the presumption, left-handed people frequently have a dominant left hemisphere. Roughly 5% of the world's population (all areas, rich or poor, black or white, are equal) are left-handed to a greater or lesser degree, and yet the proportion of people whose brains have been discovered after disease or surgery to be right-sided is much smaller. Similarly, it is a great rarity for speech to be controlled from the right-hand side, but again this is information which is only encountered by chance, and there is plenty of disagreement in the literature over the occurrence of left-handers with right speech, right-handers with right speech, and so forth.

The Economist once had a buoyant article on the Declaration of Human Lefts. Why it asked, are those of the left camp gauche and sinister, whereas the right-handers are not only right but dexterous and righteous? Whence this prejudice, which also stamps radical politics as leftward of conservatism? The sinistral, as left-handers call themselves, have reason also to resent the designs of things which favor right-handers, as well as the traditional association of left with wrong. One ardent sinistral even totted up biblical references to rightness: he discovered 1,600, most of which were hostile to the left. Although animals, such as the higher apes, tend to favors either one hand or the other and are not markedly ambidextrous (another loaded word, meaning right on both sides), they do not show a particular preference for their right side.

Man has been prejudiced ever since he has been able to record the fact. Most hand imprints on cave walls are of the left hand, indicating an Aurignacian preference for working with the right. Military burials after the early battles consist of bones more grievously injured on their left side, indicating right-handed attackers. Castle bastions and keeps possess staircases which spiral upwards in a clockwise fashion; right-handed swordsmen find them easier to defend. Scripts used to make use of the ox-turn system, ranging back and forth alternately, but most now favour right-handers as they run from left to right. Hebrew and Arabic are exceptions, and for thousands of years, China was impartial by being vertical. Chinese custom has now been overturned, and the new cultural rule is to go from left to right. Most countries drive on the right, and most people walk on the right pavement irrespective of the driving laws in their country. Presumably, both are linked with the preference for keeping the right arm in the clear.

The pressure to conform, a strong and insidious force on its own, used to be abetted in the classroom by a reluctance to entertain left-handed writing. There is some evidence that such compulsion often went hand in hand with stammering, but there is also more recent evidence that it does not. Perhaps there are changes in the definition of left-handedness which have influenced the evidence and made it contradictory. Left-handers make use of their right hands more frequently than right-handers make use of their left, and plainly some people are only a little left-handed. Jack the Ripper, whoever he was, worked with his left hand, so did George VI, who also stammered: so did Horatio Nelson, although unwillingly for his lost right arm had been his major arm, and so do an estimated 200 million in the world today, a huge minority group that suffers from the effects, as Thomas Carlyle put it after he lost the use of his right hand, of 'probably the very oldest institution that exists'.

Clockwise, the way the sun goes in the northern hemisphere may have had its influence in the preference for the right. anti-clockwise, and sitting on the left have always been inferior, often devilish, and generally sinister.

Intelligence Man's cunning is lodged in his cerebrum, but there is no center for intelligence. This depends upon the cortex as a whole. Previous theories that the frontal cortex, being the most forward bulge of the central nervous system, was the foremost spot for intelligence have not been supported by the frequent surgical excision of large portions of its substance. Besides, even though the measurement of intelligence quotients, and whether someone is above or below the average of 100, gives an aura of unity to intelligence, it is by no means one thing. Therefore, it is unfair to expect it to have one location on the cortex as if it were control of the little toe.

Dr George Stoddard, in The Meaning of Intelligence, listed its multiplicity. He said it is 'the ability to undertake activities that are characterized by 1. difficulty, 2. complexity, 3. abstractness, 4. 5. adaptiveness to a goal, 6. social value and 7. The emergency of originals, and to maintain such activities under conditions that demand a concentration of energy and resistance to emotional forces. Similarly, Theodosis Dobzhansky said, 'What is measured by the 1.Q. is not necessarily the same as what is referred to in everyday language as intelligence, cleverness, aptitude or wit. Still, less does the 1.0. give an estimate of the value or worth of the person. It has also been said that a chimpanzee will only start scoring well on intelligence tests when another chimpanzee has set them.

On learning, Alfred North Whitehead wrote: "It is a profoundly erroneous truism, repeated by all copy books, and by eminent people when they are making speeches, that we should cultivate the habit of thinking what we are doing. The precise opposite is the case. Civilization advances by extending the number of important operations which we can perform without thinking about them.' Sir Peter Medawar, in The Uniqueness of the Individual, took Whitehead's statement a stage further to produce its converse truth. 'Learning is two-fold: we learn to make the processes of deliberate thought instinctive and automatic, and we learn to make automatic and instinctive processes the subject of discriminating thought."

The intellectual abilities of others are equally hard to comprehend at both ends of the scale. In one issue Penguin Science Survey had articles exemplifying both these two ends, the abnormally incapable and the abnormally skillful. One was dedicated to the several thousand spastic children born each year whose brain damage makes it difficult for them to draw a diamond. Normally a child can copy a circle by three, a square by five, and a diamond by seven. Two years of development, therefore, separate each achievement, all three of them seem equally elementary to the adult and yet major milestones to the struggling child, with one of them being an unattainable milestone to the average spastic.

At the other end of the scale, when normal problems shrink to nothing, was Professor A. C. Aitken of Edinburgh University. He was asked to turn it into a decimal. After four seconds he answered, giving one digit every three-quarter of a second: "point 08510638297872340425531914'. He stopped there after twenty-four seconds, discussed the matter for one minute, and then started up again. 'Yes, 191489, I can get that'. Five-second pause. '361702127659574468, now that's the repeating point. It starts again at 085. So, if that's forty-six places, I'm right.'

EEG Appreciation of the mechanics of intelligence might take a step forward when current obscurity is diminished about the origin of electroencephalogram waves. It is already sixty years since these waves were first discovered. Towards the end of the nineteenth century, various men had shown that the brains, notably of dogs, possessed changing electric potentials, but it was up to Dr Hans Berger of Jena University to open up the subject.

For five years he applied electrodes to the human skull and he studied the fluctuating patterns of the potentials which his delicate galvanometers succeeded in recording. This psychiatrist then recorded his results: Über das Elektrenkephalogram des Menschen. For the next five years, while the world disregarded his claims, he continued to work, to record his results, and to use the same title in writing them up in the German journals. He was particularly suspected for his repeated contention that he could distinguish between different wave patterns. Recording the waves at all was improbable; differentiating the wave patterns yet more so.

Suddenly he was vindicated. Professor Adrian (later Lord Adrian) also recorded waves; the Physiological Society saw them; the 'Berger rhythm' was applauded, and electroencephalography -electric brain writing- has not looked back.

Sometimes after a child's eighth birthday the dominant rhythm, called by Berger the alpha rhythm, changes from its childish speed of 4-7 cycles a second and starts increasing to its adult frequency of ten cycles a second. Basically, it is an idling rhythm, for it is most manifest when eyes are closed and minds are empty. Its casual tremor is abolished the moment anything happens, whether the eyes actually open to see something interesting or visual images are merely imagined so that the brain records greater excitement.