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PSYB65H3 (479)
Chapter 1

Chapter 1

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University of Toronto Scarborough
Zachariah Campbell

PSYB65-Chapter One Notes • Neuropsychology is the study of the relation between behaviour and brain function. • Neuropsychology is strongly influenced by two traditional foci of experimental and theoretical investigations into brain function: the brain hypothesis, the idea that the brain is the source of behaviour; and the neuron hypothesis, the idea that the unit of brain structure and function is the neuron, or nerve cell. The Brain Hypothesis • Brain is an Old English word for the tissue found within the skull. • The brain has two almost symmetrical halves called hemispheres, one on the left side of the body and the other on the right. • Taken as a whole, the basic plan of the brain is that of a tube filled with salty fluid called cerebrospinal fluid ( CSF) that cushions the brain and may play a role in removing metabolic waste. Parts of the covering of the tube have bulged outward and folded, forming the more complicated looking surface structures that initially catch the eye. The most conspicuous outer feature of the brain is the crinkled tissue that has expanded from the front of the tube to such an ex- tent that it folds over and covers much of the rest of the brain. This outer layer is the cerebral cortex ( usually referred to as just the cortex). The word cortex, which means “ bark” in Latin, is aptly chosen both because the cortex’s folded appearance resembles the bark of a tree and because its tissue covers most of the rest of the brain. • The folds of the cortex are called gyri, and the creases between them are called sulci ( gyrus is Greek for “ circle” and sulcus is Greek for “ trench”). Some large sulci are called fissures, such as the longitudinal fissure that divides the two hemispheres and the lateral fissure that divides each hemisphere into halves ( in our fist analogy, the lateral fissure is the crease separating the thumb from the other fingers). • The cortex of each hemisphere is divided into four lobes, named after the skull bones beneath which they lie. The temporal lobe is located at approximately the same place as the thumb on your upraised fist. Lying immediately above the temporal lobe is the frontal lobe, so called because it is located at the front of the brain. The parietal lobe is located behind the frontal lobe, and the occipital lobe constitutes the area at the back of each hemisphere. The brain’s hemispheres are connected by pathways called commissures, the largest of which is the corpus callosum. • The cerebral cortex constitutes most of the forebrain, so named because it develops from the front part of the tube that makes up an embryo’s primitive brain. The remaining “ tube” underlying the cortex is referred to as the brainstem. The brainstem is in turn connected to the spinal cord, which descends down the back in the vertebral column. To visualize the relations among these parts of the brain, again imagine your upraised fist: the folded fingers represent the cortex, the heel of the hand represents the brainstem, and the arm rep-resents the spinal cord. • Functionally, the forebrain mediates cognitive functions; the brainstem mediates regulatory functions such as eating, drinking, and moving; and the spinal cord is responsible for sending commands to the muscles. • the brain and spinal cord together are called the central nervous system or CNS. The central nervous system is connected to the rest of the body through nerve fibers. • Some nerve fibers carry information away from the CNS, and others bring information to it. These fibers constitute the peripheral nervous system, or PNS. One of the many distinguishing features of the CNS is that, after damage, it does not regenerate lost tissue whereas PNS tissue will regrow after damage. • Organized into sensory pathways, collections of fibers carry messages for specific sensory systems, such as hearing, vision, and touch. Sensory pathways carry information collected on one side of the body mainly to the cortex in the opposite hemisphere by means of a subdivision of the PNS called the somatic nervous system ( SNS). The brain uses this information to construct its current images of the world, its memories of past events, and its expectations about the future. • Motor pathways are the groups of nerve fibers that connect the brain and spinal cord to the body’s muscles through the SNS. The movements produced by motor pathways include the eye movements that you are using to read this book, the hand movements that you make while turning the pages, and the posture of your body as you read. • Sensory and motor pathways also influence the muscles of your internal organs, such as the beating of your heart, the contractions of your stomach, and the raising and lowering of your diaphragm, which inflates and deflates your lungs. The pathways that control these organs are a subdivision of the PNS called the autonomic nervous system (ANS). • Among the oldest surviving recorded hypotheses are those of two Greeks, Alcmaeon of Croton (ca. 500 B. C.) and Empedocles of Acragas (ca. 490– 430 B. C.). Alcmaeon located mental processes in the brain and so subscribed to the brain hypothesis; Empedocles located them in the heart and so subscribed to what could be called the cardiac hypothesis. Aristotle: The Mind • The Greek philosopher Aristotle (348– 322 B. C.) was the first person to develop a formal theory of behaviour. He proposed that a nonmaterial psyche was responsible for human thoughts, perceptions, and emotions and for such processes as imagination, opinion, desire, pleasure, pain, memory, and reason. • The philosophical position that a person’s mind is responsible for behavior is called mentalism, meaning “ of the mind.” Descartes: The Mind-Body Problem • Modern thinking about this idea began with René Descartes (1596– 1650), a French anatomist and philosopher who described a relation between the mind and the brain. • Described as nonmaterial and without spatial extent, the mind, as Descartes saw it, was different from the body. The body operated on principles similar to those of a machine, but the mind decided what movements the machine should make. Descartes located the site of action of the mind in the pineal body, a small structure high in the brainstem. His choice of this structure was based on the logic that the pineal body is the only structure in the nervous system not composed of two bilaterally symmetrical halves and moreover that it is located close to the ventricles. His idea was that the mind, working through the pineal body, controlled valves that allowed CSF to flow from the ventricles through nerves to muscles, filling them and making them move. • The position that mind and body are separate but can interact is called dualism, to indicate that behaviour is caused by two things. Descartes’s dualism originated what came to be known as the mind– body problem: for Descartes, a person is capable of being conscious and rational only because of having a mind, but how can a nonmaterial mind produce movements in a material body? To understand the problem, consider that, in order for the mind to affect the body, it would have to expend energy, adding new energy to the material world. The spontaneous creation of new energy violates a fundamental law of physics, the law of conservation of matter and energy. Thus, dualists who argue that mind and body interact causally cannot explain how. • Philosophers called monists avoid the mind– body problem by postulating that the mind and body are simply a unitary whole. • By the middle of the nineteenth century, another theory of the brain and behaviour was taking shape: the modern perspective of materialism, the idea that rational behaviour can be fully explained by the working of the nervous system without any need to refer to a nonmaterial mind. This perspective had its roots in the evolutionary theories of two English naturalists, Alfred Russell Wallace (1823– 1913) and Charles Darwin (1809– 1892). • In Darwin’s terms, all living things are said to have common descent. As the descendants of that original organism spread into various habitats through millions of years, they developed structural and behavioural adaptations that suited them for new ways of life. At the same time, they retained many similar characteristics that reveal their relatedness to one another. Localization of Function • The first general theory to present the idea that different parts of the brain have different functions was developed by German anatomist Franz Josef Gall (1758– (1758– 1828) and his partner Johann Casper Spurzheim (1776– 1832). Gall and Spurzheim proposed that the cortex and its gyri were functioning parts of the brain and not just coverings for the pineal body. They supported their position by showing through dissection that the brain’s most distinctive motor pathway, the corticospinal (cortex to spinal cord) tract, leads from the cortex of each hemisphere to the spinal cord on the opposite side of the body. Thus, they suggested, the cortex sends instructions to the spinal cord to command movement of the muscles. • Gall developed a general theory of how the brain might produce differences in individual abilities into a theory called localization of function. For example, Gall proposed that a well- developed memory area of the cortex located behind the eyes would cause the eyes to protrude. You might note that aliens featured in science fiction movies are often portrayed as having bulging foreheads, reminiscent of Gall’s idea that the frontal lobes are the seat of intelligence. • Spurzheim called the study of the relation between the skull’s surface features and a person’s faculties phrenology (phren is a Greek word for “ mind”). The map of the relation between brain functions and the skull surface is called a phrenological map. • Phrenology was seized on by some people as a means of making personality assessments. They developed a method called cranioscopy, in which a device was placed around the skull to measure the bumps and depressions there. These measures were then correlated with the phrenological map to determine the person’s likely behavioural traits. • Bouillaud argued from clinical studies that certain functions are local-ized in the cortex and, specifically, that speech is localized in the frontal lobes, in accordance with Gall’s theory. • He demonstrated that language was localized; thus different regions of the cortex could have specialized functions. He also discovered something new: functions could be localized to a side of the brain, a property that is referred to as lateralization. • Because speech is thought to be central to human consciousness, the left hemisphere is frequently referred to as the dominant hemisphere, to recognize its special role in language. In recognition of Broca’s contribution, the anterior speech region of the brain is called Broca’s area, and the syndrome that results from its damage is called Broca’s aphasia. • Wernicke was aware that the part of the cortex that receives the sensory pathway, or projection, from the ear— and is thus called the auditory cortex— is located in the temporal lobe, behind Broca’s area. He therefore suspected a relation between the functioning of hearing and that of speech, and he described cases in which aphasic patients had lesions in this auditory projection area that differed from those described by Broca in four ways: 1. Damage was evident in the first temporal gyrus. 2. No opposite- side paralysis was observed (Broca’s aphasia is frequently associated with paralysis of the right arm and leg, as described for Tan). 3. Patients could speak fluently, but what they said was confused and made little sense (Broca’s patients could not articulate, but they seemed to understand the meaning of words). 4. Although the patients were able to hear, they could neither understand nor repeat what was said to them. Wernicke’s finding that the temporal lobe also is implicated in language dis-proved the strict localizationists’ view. Wernicke’s syndrome is sometimes called temporal- lobe temporal-lobe aphasia or fluent aphasia, to emphasize that the person can say words, but is more frequently called Wernicke’s aphasia. The region of th
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