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Chapter 1

NeuroPsych Chapter 1.doc

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Ayesha Khan

Chapter 1: The Development of Neuropsychology Traumatic Brain Injury (TBI) a wound to the brain that results from a blow to the head. Of these patients, 235, 000 are hospitalized and 50, 000 die. Memory and attention are abilities that are required for effectively dealing with everyday problem solving, a mental skill referred to as executive function. Thus L.D. (from case study) was able to play golf because it require that he deal with only one act at a time but he cannot prepare a meal because doing so requires that he keep track of a number of things at the same time. Neuropsychology: the study of the relation between behaviour and brain function. It draws information from many disciplines: anatomy, biology, biophysics, ethology, pharmacology, physiology, physiological psychology, and philosophy among them. Its central focus is to develop a science of human behaviour based on the function of the human brain. 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: What is the Brain? 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 surfaces structures. The most conspicuous outer feature of the brain is the crinkled tissue that has expanded from the front of the tube to such an extent that if folds over and covers much of the rest of the brain. This outer layer is the cerebral cortex: layer of gray matter on the surface of the cerebral hemispheres and composed of neurons and their synaptic connections, which form from four to six sublayers. The folds of the cortex are called gyri, and the creases between them are called sulci. 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 The cortex of each hemisphere is divided into four lobes, named after the skull bones beneath which they lie. The temporal lobe is found laterally on the head, below the lateral sulci adjacent to the temporal bones. Lying immediately above the temporal lobe is the frontal lobe: all the neocortex forward of the central sulcus. It is located at the front of the brain. The parietal lobe is the general region of the brain lying beneath the parietal lobe. The occipital lobe is the general area of the cortex lying in the back part of the head. The brains hemispheres are connected by pathways called commissures, the largest of which is the corpus callosum: the fiber system connecting the homotopic areas of the two hemispheres. A split-brain patient is one whose corpus callosum has been severed. The cerebral cortex constitutes most of the forebrain, so named because it developsfrom the front part of the tube that makes up an embryos primitive brain. The remaining tube underlying the cortex is reffered to as the brain stem. The brainstem is in turn connected to the spinal cord, which descends down the back in the vertebral column. The forebrain mediates cognitive functions; the brainstem mediates regulatory functions such as eating, drinking, and moving; and the spinal cord is responsible or sending commands to the muscles. Neuropsychologists commonly refer to functions performed in the forebrain as higher functions because they include thinking, perception and planning. How is the Brain Related to the Rest of the Nervous System? The brain and spinal cord together encased in bones are called the central nervous system (CNS). CNS 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 (PNS). CNS does not regenerate tissue, but PNS does. Nerve fibers that brings information to the CNS are extensively connected to sensory receptors on the bodys surface, to internal body organs, and to muscles, enabling the brain to sense what goes on in the world around us and within our bodies. Organized into sensory pathways, collections of fibers carry messages for specific sensory systems for specific sensory systems, such as hearing, vision, and touch. These 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 construct somatic nervous system (SNS). Motor pathways are the groups of nerve fibers that connect the brain and spinal cord to the bodys muscles through the SNS. The parts of the cortex that produce movement mainly use motor pathways to muscles on the opposite side of the body. The pathways that control these organs are a subdivision of the PNS called the autonomic nervous system (ANS). Figure 1.2: The Brain Versus the Heart: Alcmaeon of Croton (500B.C.) located mental processes in the brain and so subscribed to the brain hypothesis. Emedocles of Acragas (490-430 B.C) located them in the heart and so subscribed to what could be called the cardiac hypothesis. Hippocrates (460-377 B.C.) and Galen (A.D. 129-199), influenced by their clinical experience, described aspects of the brains anatomy and argued strongly for the brain hypothesis. o Galen worked for 5 years to point out that brain damage impairs function, but also that the nerves from the sense organs go to the brain and not to the heart. He also noted that pressure on the brain causes cessation of movement and death, whereas pressureon the heart causes pain but does not arrest voluntary behaviour. Aristotle: The Mind Aristotle (38-322 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. It worked through heart. o Adopted by Christianity in its concept of the soul. o Mind = memory and psyche = mind The philosophical position that a persons mind is responsible for behaviour is called mentalism, meaning of the mind. o Influenced sensation, perception, attention, imagination, emotion, memory and volition Descartes: the Mind-Body Problem Rene 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. o Descartes located the site of action of the mind in the pineal body, small structure high in the brainstem. This 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. o Descartes Concept of Reflex Action: in this mechanistic depiction of how Descartes thought physical reflexes might work, heat from the flame causes a thread in the nerve to be pulled, released ventricular fluid through an opened pore. The fluid flows through the nerve, causing not only the foot to withdraw but the eyes and head to turn to look at it, the hands to advance, and the whole body to bend to protect it. Descartes applied the reflex concept to behaviours that today are too complex to be reflexive, whereas he did not conceive of behaviour described as reflexive today. Today, the pineal body, known as the pineal gland is thought to take part in controlling biorhythms. Furthermore the cortex became much more central to understanding behaviour. The position that mind and body are separate but can interact is called dualism, to indicate that behaviour is caused by two things. Descartes 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? o Body can affect the mind but the mind cannot affect the body avoid problem; body function is parallel Other philosophers called monists avoid the mind-body problem by postul
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