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Chapter 3

Chapter 3 Part II PS101.docx

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Carolyn Ensley

PS101 Chapter 3 – The Biological Bases of Behaviour Week 5 The Brain and Behaviour -The brain can be divided into three major regions: the hindbrain, the midbrain, and the forebrain The Hindbrain -The hindbrain includes the cerebellum and two structures found in the lower part of the brainstem: the medulla and the pons -The medulla, which attaches to the spinal cord, is in charge of largely unconscious but vital functions, including circulating blood, breathing, maintaining muscle tone, and regulating reflexes such as sneezing, coughing, and salivating -The pons include a bridge of fibres that connects the brainstem with the cerebellum. They also contain several clusters of cell bodies involved with sleep and arousal -The cerebellum is a large and deeply folded structure locate adjacent to the back surface of the brainstem. It is critical to the coordination of movement and to the sense of equilibrium, or physical balance -The cerebellum plays a key role in organizing the sensory information that guides these movements – it allows you to hold your hand out to the side and then smoothly bring your finger to a stop on your nose -Damage to the cerebellum disrupts fine motor skills, such as writing, typing or playing a musical instrument The Midbrain -The midbrain is the segment of the brainstem that lies between the hindbrain and the forebrain -Contains an aea that is concerned with integrating sensory processes, such as vision and hearing -The dopamine system within the midbrain is involved in the performance o voluntary movements -The decline in dopamine synthesis causes Parkinson’s -Running through both the hindbrain and the midbrain is the reticular formation which contributes to the modulation of muscle reflexes, breathing, and pain perception -It is best known for its role in the regulation of sleep and arousal The Forebrain -The forebrain is the largest and most complex region of the brain, encompassing a variety of structures, including the thalamus, hypothalamus, limbic system, and cerebrum The Thalamus: A Way Station -The thalamus is a structure in the forebrain through which all sensory information (except smell) must ass to get to the cerebral cortex -Each cluster in this system is concerned with relaying sensory information to a particular part of the cortex -Also appears to play an active role in integrating information from various senses The Hypothalamus: A Regulator Of Biological Needs -The hypothalamus is a structure found near the base of the forebrain that is involved in the regulation of basic biological needs -Lies beneath the thalamus -Contains various clusters of cells that have many key functions – one such function is to control the autonomic nervous system -Serves as a vital link between the brain and the endocrine system PS101 Chapter 3 – The Biological Bases of Behaviour Week 5 -Plays a major role in the regulation of basic biological drives related to survival: fighting, fleeing, feeding, and mating -The hypothalamus contributes to the control of hunger and other basic biological processes, including thirst and temperature regulation The Limbic System: The Seat of Emotion -The limbic system is a loosely connected network of structures located roughly along the border between the cerebral cortex an deeper subcortical areas -The limbic system is not a well-defined anatomical system with clear boundaries -Broadly defined, the limbic system includes parts of the thalamus and hypothalamus, the hippocampus, the amygdala, and other structures -Involved in the regulation of emotion, memory and motivation and recently been linked to people’s optimistic approach to life -The hippocampus and adjacent structures play a role in memory -Consolidation involves the conversion of information into a durable de -Hippocampus also plays a role in prediction and imagination -There is ample evidence linking the limbic system to the experience of emotion, but the exact mechanisms are not yet well understood -Recent evidence suggests that the amygdala plays a central role in the learning of fear responses and the processing of other basic emotional responses -The limbic system is also one of the areas in the brain that appears to be rich in emotion-ringed “pleasure centres” -There are self-stimulation centres located in the brain and many of them have been found in the limbic system -Recent evidence suggests that the so-called “pleasure centres” in the brain may not be anatomical centres so much as neural circuits releasing dopamine The Cerebrum: The Seat of Complex Thought -Includes the brain areas that are responsible r the most complex mental activities including learning, remembering, thinking and consciousness itself -The cerebral cortex is the convoluted outer layer of the cerebrum -The cerebral hemispheres are the right and left halves of the cerebrum -The corpus callosum is the structure that connects the two cerebral hemispheres -Each cerebral hemisphere is divided into four parts called lobes -The occipital lobe includes the cortical area where most visual signals are sent -The parietal lobe is forward of the occipital lobe – includes the area that registers the sense of touch -The temporal lobe contains an area devoted to auditory processing -The frontal lobe contains the principal areas that control the movement of muscles The Plasticity of the Brain -The anatomical structure and functional organization of the brain are more “plastic” or malleable than widely assumed -Brain plasticity refers to the brains ability to change structure and function -Experience effects dendritic length, synapse formation, and altered metabolic activity -Neural reorganization of the brain has been seen in response to brain damage -Studies indicate that the adult brain can generate new neurons PS101 Chapter 3 – The Biological Bases of Behaviour Week 5 -Neurogenesis – the formation of new neurons -These new neurons migrate to areas in the cortex where they sprout axons and form new synapses with existing neurons, becoming fully integrated into the brain’s communication networks -Neurogenesis might contribute to the natural repair processes that occur after brain damage -Neurogenesis might contribute to learning -Stem cells are unspecialized cells that renew themselves through cell division and that can under special circumstances be induced to become cells suitable for other specialized purposes such as the beating cells of the heart -The brain is not hard wired – it appears that the neural wiring of the brain is flexible and constantly evolving – this plasticity however, is not unlimited Right Brain/Left Brain: Cerebral Laterality -The left hemisphere was implicated in the control of language -Evidence that the left hemisphere processes language led scientists to characterize it as the dominant hemisphere -The left hemisphere was given the lion’s share of credit or handling the “higher” mental processes such as reasoning, remembering, planning, and problem solving Bisecting the Brain: Split-Brain Research -In split-brain surgery, the bundle of fibres that connects the cerebral hemispheres (the corpus callosum) is cut to reduce the severity of epileptic seizures -Each hemisphere’s primary connections are to the opposite side of the body -Both eyes deliver information to both hemispheres -Auditory inputs to each ear also go to both hemispheres -Information received by one hemisphere is readily shared with the other via the corpus callosum -When the two hemispheres are surgically disconnected, the functional specialization of the brain becomes apparent -Some research suggests that the corpus callosum plays an excitatory role in which it enables activation of both hemispheres by acting as a bridge between them -Other findings suggest that it acts as an inhibitory role, preventing information from being transferred between the hemispheres Hemispheric Specialization to the Intact Brain -Split-brain procedure is unlikely and only 10 cases have been extensively studied so it is hard to generalize about it -Many other research has been done – if asked see page 115 in text -Another method involves looking at perceptual asymmetries – left-right imbalances between the cerebral hemispheres in the speed of visual or auditory processing -In normal individuals, the input sent to one hemisphere is quickly shared with the other -When verbal stimuli are presented to the right visual field, they are identified more quickly and more accurately than when they are presented to the left visual field -The faster reactions in the let hemisphere presumably occur because it can recognize presumably occur because it can recognize verbal stimuli on its own, while the right hemisphere has to take extra time to “consult” the left hemisphere -Overall, the findings suggest that the two hemispheres are specialized, with each handling certain types of cognitive tasks better than others PS101 Chapter 3 – The Biological Bases of Behaviour Week 5 -The left hemisphere usually is better on tasks involving verbal processing, such as language, speech, reading, and writing. The right hemisphere exhibits superiority on many tasks involving nonverbal processing, such as most spatial, musical, and visual recognition tasks and tasks involving the perception of others’ emotions -Hemispheric specialization is not unique to humans, as it has been observed in a variety of other species The Endocrine System: Another Way to Communicate -The endocrine system consists of glands that release hormones into the bloodstream; hormones help to
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