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Chapter 1

PSYB65 Chapter 1.doc

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Zachariah Campbell

PSYB65 – Chapter 1 The Brain Hypothesis: What is the Brain? - Brain – tissue found within the skull - Hemispheres – 2 almost symmetrical halves that the brain has o One on the left side of the body and one on the right - Cerebrospinal fluid (CSF) – a tube filled with salty fluid o Cushions the brain and removes metabolic waste - Cerebral cortex – The outer layer of the brain which is crinkled tissue that has expanded from the front of the tube to an extent that it folds over and covers much of the rest of the brain o Gyri – the folds of the cortex o Sulci – the creases between the folds  Fissures – large sulci, examples: • Longitudinal fissure divides the two hemispheres • Lateral fissure divides each hemisphere into halves o The cortex of each hemisphere is divided into 4 lobes:  Temporal lobe – located at the same place as the thumb on your upraised fist  Frontal lobe – lies immediately above the temporal lobe, located at the front of the brain  Parietal lobe – located behind the frontal lobe  Occipital lobe – the area at the back of each hemisphere o Commissures – pathways that connect the brain’s hemispheres  Corpus callosum – the largest commissure - Forebrain – the cerebral cortex constitutes most of the forebrain, because it develops from the front part of the tube that makes up an embryo’s primitive brain o Mediates cognitive functions o Functions performed in forebrain are known as higher functions because they include thinking, perception and planning - Brain stem – the remaining tube underlying the cortex o Mediates regulatory functions such as eating, drinking and moving - Spinal cord – connected to the brainstem, which descends down the back in the vertebral column o Responsible for sending commands to the muscles How is the Brain Related to the Rest of the Nervous System? - The brain and spinal cord in mammals are protected by bones: o The skull protects the brain o The vertebrae protect the spinal cord - Central nervous system (CNS) – consists of the brain and spinal cord because both are enclosed within the protective covering o The CNS is connected to the rest of the body through nerve fibers  Some nerve fibers carry information away from the CNS, others bring information to it. o After damage, it does not regenerate lost tissue - Peripheral nervous system (PNS) – constitutes of the nerve fibers o PNS tissue will re-grow after damage o Nerve fibers are connected to sensory receptors on the body’s surface, internal body organs and muscles, enabling the brain to sense environmental changes  Sensory pathways – collections of fibers carrying messages for specific sensory systems. o Somatic nervous system (SNS) – a subdivision of the PNS where sensory pathways carry information collected on one side of the body to the cortex in the opposite hemisphere  Motor pathways – groups of nerve fibers that connect the brain and spinal cord to the body’s muscles through the SNS. o Autonomic nervous system (ANS) – a subdivision of the PNS, where sensory and motor pathways influence the muscles of internal organs.  Such as, beating of the heart, contractions of the stomach and lungs The Brain Vs the Heart: - Alcmaeon of Croton – located mental processes in the brain and so subscribed to the brain hypothesis - Empedocles of Acragas – located them in the heart and so subscribed to the cardiac hypothesis - Early physicians, influenced by their clinical experience, described aspects of the brain’s anatomy and argued strongly for the brain hypothesis o Hippocrates o Galen – proved that the cardiac hypothesis was wrong,  Pointed out not only that brain damage impairs function but also that the nerves from the sense organs go to the brain and not to the heart.  Noted that pressure on the brain causes the cessation of movement and even death, but pressure on the heart causes pain and not voluntary behaviour Aristotle: The Mind: - Aristotle – was the first person to develop a formal theory of behaviour. o Proposed that a nonmaterial psyche was responsible for human thoughts, perceptions and emotions  Processes as imagination, opinion, desire, pleasure, pain, memory and reason o The psyche was independent of the body but in Aristotle’s view, worked through the heart to produce action. - Mentalism – the philosophical position that a person’s mind is responsible for behaviour o Influenced people’s ideas about how the brain might work because, the brain was thought to work as a whole. Descartes: The Mind-Body Problem: - Rene Descartes – described a relation between the mind and the brain o Believed that the mind, described as nonmaterial and without spatial extent, was different from the body o He located the site of action of the mind in the pineal body, the structure in the brainstem  This was the only structure in the nervous system not composed of 2 bilaterally symmetrical halves and is located close to the ventricles. o 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 o The pineal body is also known as the pineal gland  Thought to take part in controlling biorhythms - Dualism – the position that mind and body are separate but can interact o For him, the person is capable of being conscious and rational only because of having a mind o But how can a nonmaterial mind produce movements in a material body?  Monists – philosophers who avoid the mind-body problem by postulating that the mind and body are simply a unitary whole - Descartes also proposed that animals do not have minds and so are only machinelike o Animals did not have a mind o A child developed a mind when about at 7 years old when they were able to talk and reason o The mentally ill had lost their minds - He proposed that the key indications of the presence of a mind are the use of language and reason Darwin and Materialism: - 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 o Alfred Russell Wallace o Charles Darwin - They both looked at structures of plants and animals and at animal behaviour  Observations lead to the idea that the similarities could be explained if all animals evolved from a common ancestor - Darwin said that all living things had common descent o As the descendants of that original organism spread into various habitats throughout millions of years:  They developed structural and behavioural adaptations suited for new ways of life; also retaining similar characteristics at the same time Experimental Approaches to Brain Function: - Quantitative methods used to test ideas about brain function Localization of Function: - Franz Josef Gall & Johann Casper Spurzheim – first general theory to present the idea that different parts of the brain have different functions o Supported through dissection that the brain’s most distinctive motor pathway, the corticospinal tract leads from the cortex of each hemisphere to the spinal cord on the opposite side of the body  Suggested that the cortex sends instructions to the spinal cord to command movement of the muscles o Also proposed that it produces behaviour through the control of other parts of the brain and spinal cord through the corticospinal tract  Recognized that the 2 hemispheres of the brain are connected by the corpus callosum and can interact - Localization of function – theory that Gall developed of how the brain might produce differences in individual abilities o Proposed that a bump on the skull indicated a well-developed underlying cortical gyrus and therefore a greater capacity for a particular behaviour, examples:  High degree of muscle ability and artistic talent would cause large bumps in particular areas of the skull  Depression in the same area indicated an underdeveloped gyrus and alongside reduced faculty - Phrenology – the study of the relation between the skull’s surface features and a person’s faculties that Spurzheim called: o Phrenological map – the map of the relation between brain functions and the skull surface o Cranioscopy – a method in which a device was placed around the skull to measure the bumps and depressions there  These measures correlated with the phrenological map to determine the person’s likely behavioural traits • However, phrenologists failed to recognize that the superficial features of the skull reveal little about the underlying brain Localization and Lateralization of Language: - Jean Baptiste Bouilaud – argued from clinical studies that certain functions are localized in the cortex o Specifically, speech is localized in the frontal lobes. o Also suggested that the part of the brain that controls right hand movements might be the left hemisphere - Ernest Auburtin – reported the case of a patient who lost the ability to speak when pressure was applied to his exposed frontal lobe - Paul Broca – worked with Auburtin to confirm that the left frontal lobe was the focus of a patient understanding but unable to produce speech o Discovered that functions could be localized to a side of the brain, referred to as lateralization o Speech is thought to be central to human consciousness, so the left hemisphere is frequently referred to as the dominant hemisphere  The anterior speech region of the brain is now called Broca’s area  The syndrome that results from its damage is called Broca’s aphasia - Pierre Marie – reexamined the preserved brains of Broca’s first two patients o Found that Tan (one of the patients) had additional extensive damage in his posterior cortex that could have accounted for his aphasia Sequential Programming and Disconnection: - Strict localizationists – people who interpreted Broca’s findings as evidence that language resides totally in one part of the brain - Carl Wernicke – first scientist to dissent from Broca’s findings o He was aware that part of the cortex that receives the sensory pathway from the ear (called the auditory cortex) is located in the temporal lobe, behind Broca’s area o He suspected a relation between the functioning of hearing and that of speech - He described cases in which aphasic patients had lesions in the auditory projection area that differed from those described by Broca in 4 ways: o Damage was evident in the first temporal gyrus o No opposite-side paralysis was observed (Broca’s aphasia frequently associated with paralysis of the right arm and leg) o Patients could speak fluently, but their speech was confused and made little sense o Although the patients were able to hear, they could neither understand nor repeat what was said to them - Wernicke’s syndrome is frequently called Wernicke’s aphasia o Other names also used:  Temporal-lobe aphasia  Fluent aphasia o Wernicke’s area - the region of the temporal lobe associated with this form of aphasia - He proposed that auditory information travels to the temporal lobes from the ears o In Wernicke’s area, sounds are processed into auditory images or ideas of objects and stored o Auditory ideas can be sent through a pathway called arcuate fasciulus  Pathway leads to Broca’s area, where the representations of speech movements are stored  From Broca’s area, neural instructions are sent to muscles that control movements of the mouth to produce the appropriate sounds. o If the temporal lobe were damaged, speech movements could still be mediated by Broca’s area but the speech would make no sense, because the person would be unable to monitor words. o Since damage to Broca’s area produces a loss of speech movements without the loss of sound images, Broca’s aphasia is not accompanied by the loss of understanding. - He also predicted a new language disorder o Suggested that if the arcuate fibers connecting the two speech areas were cut, disconnecting the areas but without inflicting damage on either one, a speech deficit described as conduction aphasia would result.  Speech sounds and movements are retained, but speech is still impaired because the person cannot judge the sense of the words that he or she heard  This was confirmed and is now sometimes called the Wernicke- Geschwind model - Joeseph Dejerine – described a case in which the loss of the ability to read (alexia) resulted from a disconnection between the visual area of the brain and Wernicke’s area - Hugo Leipmann – able to show that an inability to make sequences of movement (apraxia) resulted from the disconnection of motor areas from sensory areas Loss and Recovery of Function: - Pierre Flourens – his experimental method consisted of removing parts of the brains of animals to study any changes in behaviour produced by these surgeries o He removed a small piece of cortex and then observed how the animal behaved and how it recovered from the loss of brain tissue o Found that parts of the brainstem have specialized functions  The brainstem is important for breathing, because animals suffocated if the brainstem had been damaged  Also found that the cerebellum, part of the brainstem, coordinates locomotion - Friedrich L. Goltz – confirmed Flouren’s findings o Argued that if a part of the cortex had a function, then its removal should lead to a loss of that function o Experimented by removing cortex on 3 dogs  Result showed that the removal of cortex did not appear to eliminate any function completely, but reduced all functions to some extent Hierarchical Organization and Distributed Systems in the Brain: - John Hughlings-Jackson – resolved the fundamental disagreement between experiments that appeared to support localization of function and those that did not by the hierarchical organization concept of brain function o Proposed that the nervous system was organized as a functional hierarchy  Each successively higher level controlled more complex aspects of behaviour and did so by means of the lower levels o He described the nervous system as having 3 levels:  Spinal cord  Brain stem  Forebrain o He suggested that diseases or damage that affect the highest levels of the brain hierarchy would produce dissolution, the reverse of evolution  Animals would still have a repertoire of behaviours, but the behaviours would be simpler The Binding Problem: - William B. Scoville (neurosurgeon) – bilaterally removed the medial parts of the temporal lobes from patient, H.M. for the treatment of epilepsy
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