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Chapter 4

Chapter 4 - Psychobiology, Neuroscience.docx

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PSYC 200
Michael Boyes

CHAPTER 4 Psychobiology: Neuroscience – Brain and Behaviour Green Canadian Flag • After image: red/purple, indistinct shape • Theory: some neurons more likely to be fired in the presence of green than other colours o Taking away that color should have no effect • The fact that afterimage is seen suggests that more complicated explanation is needed • Not a graded function o Either on or off o Enhance experience by having neuron turn on and off more often • Resting/baseline rate of firing • Theory: neuron susceptive to both green and red o Fires faster when green o Red – fires slower • Refractory/resting phase – drops firing rate below baseline o Interprets lower firing rate as red • Opponent process cells o Green – fast o Red – slow • Red-green colourblind o Process under-functions Nervous System Hierarchy Central Peripheral nervous system – relay messages, CNS nervous system Brai Spinal Somatic Autonomic nervous system n cord nervous system Controls involuntary body functions Connects Controls • E.g. maintain body temperature – tight brain and voluntary parameters (fever; hypothermia – triage, body periphera muscles and gives up on extremities, focuses on central l nervous transmits core) system sensory • Homeostasis – process where number of information to the features come together to maintain some CNS aspect (temperature, hydration, appetite, etc.) • Done through opposing systems Sympathetic Parasympathetic nervous system nervous system Arouses body to Calms body to conserve 1 expend energy and maintain energy Central Nervous System (CNS) • Brain o 2% of body weight, uses ~20% of resources (glucose, oxygen) o Composed of bunches of neurons, which form nerves • Spinal cord o Complex tangle of nerves that stretch from brain to tailbone o Collects & transmits info between brain and peripheral nervous system  Processing sensory information – e.g. balance o Initiates reflexes: automatic response to an event  Kick reaction (hammer)  Checked extensively in newborns and infants – how well their nervous system is functioning Peripheral Nervous System (PNS) • PNS links the CNS to the organs, muscles, and glands of the body • Two parts: o Somatic (SNS): nerves controlling voluntary muscle movements  Walking, moving around  Muscles get stiff from exertion o Autonomic (ANS): controls glands, organs, blood vessels  Drives the regular functioning as well as flight-or fight response  Sympathetic – arouses body to prepare for action (fight or flight; third option – freeze; e.g. mouse) • Pupils dilate • Salivation decreases – fluid needed to hydrate cells • Skin sweats • Bronchi dilate: breathe more rapidly, shallowly – more efficient at processing oxygen • Heartbeat speeds up • Digestion is inhibited – need blood to carry oxygen to large muscle groups and brain  Parasympathetic – slows down body to reserve energy • Pupils contract • Salivation increases • Skin (palm) is dry • Bronchi constrict: breathe more slowly, deeply o Post-exertion asthma – push in sympathetic system opened things up; rebound effect • Heartbeat slows down 2 • Digestion is stimulated • Tear ducts turned on • Sympathetic and parasympathetic evolved for short-term stressful events o Modern-day stress – long-term basis  Physiological impact: top 8 prescriptions in GP’s offices are due to moderate, long-term effects of stress (high blood pressure, anxiety, depression, stomach issues) o Manage sympathetic nervous system – calm down, lower general levels of functioning  Exercise, relaxation/meditation Neuron Structure • Neurons – nerve cells • Mechanism by which communication occurs: o Bring sensory information to the brain o Store memories (formation/retrieval), reach decisions o Control activity of the muscles • Variety of sizes and shapes – driven by other neurons that they’re connected to • Basic cell – has nucleus o Nucleus – metabolism of cell, nutrients drawn in • Four principle parts: o Soma – cell body  Controls metabolism and cell maintenance  Receives messages from other neurons o Dendrites – tree-like growth that are attached to the soma  Function – to receive information from other neurons and carry them to the soma (input)  Means by which (in close proximity to) neuron is connected to other neurons o Axon – carries messages away from the soma to the other cells with which the neuron communicates (output) when an axon is stimulated at one end it sends a message called the action potential 3  Main feature of a neuron – fires/electrical impulse triggered in nucleus area travels down to axon • Axon terminals – release of neurochemical substances  travel across gap  influence neighbouring neurons  Many insulated with myelin – speeds nerve conduction • Multiple sclerosis – degradation of myelin  All or none response of action potential • Adjust nature of firing by changing frequency – more excited = higher rate of firing o Terminal buttons – located at the ends of the “twigs” that branch off the axon  Secrete a chemical called a neurotransmitter or transmitter substances whenever an action potential is sent to them from the axon  This transmitter substance affects the activity of the other cells Action Potential • Axons of resting neurons are negatively c+arged (inside) • When stimulated to “fire”, sodium (Na ) gates open and positively charged ions rush in changing the cell polarity in that area • Shortly (3ms), those gates close and potassium (K ) gates open and potassium ions leave the axon area, returning it to a negative charge (resting potential) • Cell either fires or doesn’t o Myelin speeds up rate at which action potential moves along Synaptic Transmission • Neurons communicate by means of synapses • Synapse – conjunction of a terminal button of one neuron with the somatic or dendritic membrane of another neuron • Two types of synapses: 4 o Excitatory synapses – upon activation by an action potential, releases a transmitter substance that excites the neurons on which they synapse  More likely that these neurons will “fire” (send an action potential down their axon) o Inhibitory synapses – upon activation, lower the probability that the axon of the post synaptic neuron will fire • Excitatory and inhibitory chemicals are stored within the synaptic vesicles within the terminal buttons • Baseline firing rate o Fires more often than usual – excitatory phase o Fires at a lower rate than usual – inhibitory phase • Neurotransmitters released into fluid-filled space  binds like a key to a specific receptor • Recording microelectrodes can measure firing rate • Excitation or inhibition is brief o Chemical are deactivated – transmitter substance is destroyed by an enzyme or (more commonly) there is reuptake o Chemical is released at the terminal button and then quickly reabsorbed (taken up again) o Specific enzymes Influencing Neuronal Activity • Medicinally and recreationally • Synthesize neurotransmitters and pump them in 5 o Hallucinogens (LSD), L-DOPA o Inject, ingest, implant into brain o Timothy Leary – accomplished personality theorist at Princeton, promoted use of LSD in 1960s o L-DOPA – synthetic version of dopamine  Treat Parkinson’s disease – underproduction of dopamine in motor control areas (tremors  little to no motor control)  Catastrophic side effects • Schizophrenia – hallucinations; consequence of overproduction of dopamine  Physical system adapts to higher levels – increase dosage o Oliver Sachs – famous neuroscientist o Sleeping sickness – comatose patients  Childhood exposure to polio  Physician used L-DOPA – some patients woke up  Dosage wore off  patients went back to sleep o Difficulty with control  Dosage, targeted areas, messing up other systems  Solution: targeted delivery • Target their delivery o Transplants o Genetically-modified mice with Parkinson’s ▯ transplant healthy mouse brain tissue into diseased brain • Block their delivery o Curare – natural neurotoxin  Used occasionally in human surgery (plastic surgery)  Curare doesn’t block pain receptor systems, doesn’t put person to sleep • Need to manage heart o Blocks up receptor sites in motor control system  paralysis • Block their destruction o Beta blockers – blocks breakdown of serotonin (enzyme inhibited) o Transmitter stays in cleft longer  more chance of binding with receptor  Depression, anxiety • Block their reabsorption o SSRI’s (selective serotonin reuptake inhibitors) – block reabsorption process o More transmitters made available o Issue: depression – patients should show improvement in 24-48 hours of taking SSRIs  Actually takes a week or more o E.g. polar bear depression  Obsessive compulsive pacing  Prozac remarkably effective 6 • Ecstasy - all of serotonin in vesicles gets dumped out o Euphoric manic high o Consequence:  Second hits don’t work – no serotonin left  Used over long time  clinical depression (not enough serotonin in system, not fully replaced) The Brain • Broca and Wernicke – specific areas of brain involved in specific functions o Post-mortem analyses o Broca’s area – lost ability to speak o Wernicke’s area – lost ability to understand spoken language • Be open to possibility that an area is involved in different functions o Homeostatic balance o Root/passage/conduit for information going to another place • Concussions in sports o Lou Geric’s disease • Ways to study the brain: o Studied in real time o Electrical recordings – electrodes  Fire less/more frequently in resence of certain behaviours/stimulation o EEG – measures electrical activity of thousands of neurons  General level of electrical activity in brain monitored – general geographic regions more/less active under different circumstances • Listening, looking, processing, verbally responding  Placed on surface of head  ADHD – which areas of brain over/under-functioning • Frontal area – less functioning (Phineas Gage) • Can study effects of brain damage o Lesioning – cutting/damaging specific fibers/cells in a particular area of the brain  Sometimes used to reduce impact of OCD  Used in rats to observe functions of brain o Ablation – removal of a portion of the brain  Wilder Penfield – circuits of memory in brain • Sections of rat brains removed – rats still capable of showing that they had the memory o Stimulation – implant electrode through which microelectric shock is delivered  Shock causes neurons to fire  Look at impact of stimulation in particular area of brain 7 • Reward/pleasure center of brain – rat given ability to hit button to stimulate this area  becomes addicted, foregoes all other needs (food, sleep, etc.) • Punishment center – rat pushes button once to stimulate area and never pushes it again (negative reinforcement)  Ethical issues on use on humans  John Varley – author, “socket head” • Government regulations – control mechanism to be used for a few minutes a day • Phineas Gage o Early data for understanding of how brain works o Country doctor who treated him o Foreman of railway building crew  Prepare roadbed for tracks to be installed  Blast out large rocks, lower hillsides o Ideal employee as a supervisor/foreman – calm, cool, level-headed, good with his own resources, managing day-to-day work (hit quotas, made plans), thoughtful, not particularly emotional o Moved into area with more flint content in rocks  Phineas was preparing the charge – getting hole drilled, tamping down the charge  Set off the charge prematurely due to flint  rod went through cheek and up through head  Trouble hearing, blind in left eye  Seemed relatively unaffected o Behaviour changed  Impulsive – spending money  Offence at minor things  Quick to anger – fights  Couldn’t focus o Role of frontal lobe  Prefrontal lobotomy  Planning skills, focus, impulse control, delay gratification o Preschoolers – frontal lobe not fully developed (until late teens, early 20s)  No impulse control  Marshmallow test – 5 minutes Brain Imaging • Last decade – become less expensive/more common o Applied in neuroscience o Which areas of brain more/less active • CAT scan: computerized axial tomography 8 o Series of X-rays taken from different angles o Provides virtual sliced view of the brain – look a different layers/levels o Particularly useful for observing stroke damage  Over a certain size – larger than a pea o Limited: physical structure of brain over a certain size • MRI: magnetic resonance imaging (fMRI) o Higher degree of detail than CAT scan o Magnetic field used to view structural nature of brain o Useful when stroke suspected  Much smaller area of damage/more spread around • Functional magnetic resonance imaging (fMRI) o Similar picture to PET scan o Advantage: cheaper than PET, no need to ingest radioactive isotopes o Looks at subtle changes in blood flow in the brain that would directly correspond to a o More neurons firing  draw more blood • PET scan: positron emission tomography o Allows us to look at the electrical functioning in the brain – most active o IV introduced that contains simple sugar dissolved in liquid; glucose molecules tagged with low level of radioactive isotope  person in scanner  PET scan can pick up radioactive isotope as brain uses glucose 9 • Watching Superbowl commercials o Doritos – more involved in visual processing area; more engaged How Many Neurons in a Brain? • Relationship between number of neurons and intelligence o Elephant: 200,000,000,000  Most of neurons relate to motor control  Sensitive auditory processing – hear elephants miles away (vibrations) • Number of neurons relative to body size o Human beings have highest brain:body size ratio o Dolphin ratio similar to chimpanzees • Rouge test – test of self-awareness o 18 month-2 year old human children put in front of mirror  At what point do they recognize that the child in the mirror is them? o Child taken away from mirror  red lipstick put on their nose  Realize the image is theirs o Chimpanzees take the same time to become  Dolphins similar • Dolphin trained to come to particular point in pool  settle down for a few seconds  rewarded o Reinforcing behaviour o If dolphin not following instructions, given time out  Researcher walks away 15 feet, stares at dolphin for 30 seconds, then returns to training o Every once in a while, dolphin would spit out some food  Tough fins on food  Dolphin gives researcher time out if given particular section of food with tough fins Brain Structure and Function 10 Cat’s brain • Lobster – no brain; cluster of neurons o Need complex, interconnected neurons for abstract thought o Neuroscience debate: do lobsters feel pain when thrown in boiling water? • Correlation of behaviour and complexity of brain • Areas of brain: o Cerebellum o Optic nerve – primary visual processing center o Cerebrum – higher processing o Olfactory bulb – smells • Cerebellum – involved in smooth motor movements o Walking from one place to another o “Little brain” o Large in humans  Sobriety test – walk along line with eyes up o Large in cats – agile (vertical leaps) o Large in birds – airborne o Small for frogs – direction of jumps random  Compound eyes – don’t see details o A bit bigger for fish – navigation • Cerebrum – higher levels of thinking, problem-solving o Humans – deep creases  Much material – 1m across of information 11 o Not much in birds – “bird brain” o Small in frogs and fish o Cats – fair degree of complexity; folds  Basic behaviour: reactive and reflective hunters – figure out good hunting grounds, dangers  Strategic hunters • Optical nerve o Well-developed in all species • Olfactory bulb o Well-developed in humans o Particularly important to fish o Directly channeled to higher centers of brain  Strong relationship between smells and memories  Other senses processed before being taken to higher centers • Brain stem – lower stem; hind brain o Hind – older evolutionarily; most basic functions (heart rate, blood pressure, sleep/wake) o Fore brain (higher centers) – homeostatic mechanisms, more complex • Spinal cord b
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