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Chapter 4

Chapter 4 Part II

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PSYC 100
Meredith Chivers

Week 7: Chapter 4: Biology of Behaviour PART II Study of the Brain - science has advanced, we have many research methods to study the brain, identify neurons and their particular neurotransmitters Experimental Ablation - experimental ablation: surgical removal of body tissue for research - study brain and its biological processes in order to understand behaviour - current methods study how brain performs many processes including: change in response to diseases/accidents shows electrical and chemical responses responds to instructions encoded in genes - Flourens and Broca using experimental ablation: found correlation between behavioral deficit and physical disruption of a specific part of the nervous system - to study experimental effect of brain disruption in animal, investigator produces a brain lesion (aka experimental ablation) and studies its effects on the animals behaviour if a particular behavior is disrupted, damaged area must be involved in those behaviours - to make a brain lesion: anaesthetizes animal, prepared for surgery, drills hole in skull stereotaxic apparatus: device used for deep regions of brain to insert an electrode into a particular part of the brain; records electrical activity, electrically stimulates brain, or produces localized damage electrolytic lesions: produced once correct region is found, by passing electric current through electrode to heat/destroy a part of the brain - excitotoxic lesions: produced by injecting a chemical that causes lethal overstimulation of neurons - reversible lesions: produced using anaesthetics that temporarily suppress action of a region - physiological psychologists can manipulate genetic mechanisms that control the nervous system (the neurochemical version of experimental ablation) ie. theory that a specific neurotransmitter performs a certain function targeted mutation: mutated gene (knockout gene) synthesized to produce non- functional version of this neurotransmitter, which is implanted into animals; if function is eliminated, provides evidence of neurotransmitter‟s role Visualizing the Structure of the Brain - much of the brain's ability to process information is all due to physical connections of neurons to one another - different techniques are used to trace/map these connections - the brain is always changing growing in volume as an individual develops from an embryo to an adult- modified by experience even after the physical maturation is done synapses form and disappear, dendrites grow and shrink, axons become myelinated neural plasticity: the production of changes in the structure and functions of the nervous system, induced by environmental events, exhibited by the brain - techniques to trace the effects of neural plasticity done by marking or „staining‟ neurons chemically some chemical stains are good at marking a certain % of neurons and making their especially prominent (good for examining the growth of dendrites and possible changes in number of synapses) other staining techniques could highlight axonal growth, showing the way axons grow/connect with specific area of brain - to examine larger parts of brain, staining techniques used, for ex. autopsy to see location of a fatal brain injury - new techniques of radiography and nuclear medicine allow methods to look at brain of living individuals - computerized tomography (CT) scanner: uses a special X-ray machine and computer to produce images of the brain that appear as slices taken parallel to the top of the skull x-ray beams are passed through person‟s head computer calculates the amount of radiation that passes through part of the brain shows approximate location of a brain injury in a live patient (damaged area shows up as white in colour) positron emission tomography (PET): recent technique uses radioactive processes to give tomographical information person has a dose of radioactive substance metabolically, the substance is incorporated into the brain tissue where it emits a particle (the positron) particle travels for about 2 cm, hits matter, and emits a photon that is measured to construct brain image magnetic resonance imaging (MRI): person places in strong magnetic field molecules align with the lines of the magnetic force radio signal is sent around the person, tilting the aligned atoms scanner measures time taken to recover image constructed using relative amounts of different materials within the scanner, since different molecules take different amount of time to realign ie. myelinated and unmyelinated neurons recover at a different time, showing contrast b/w white matter and grey matter Measuring the Brain‟s Activity - recording techniques detect effects of APs and synaptic changes; effects can deliberately triggered using stimulation methods - brain works electrically and chemically, so methods developed for each Measuring the Brain’s Electrical Activity - microelectrode: thin electrode made of wire or glass that can measure the electrical activity of a individual neurons contains an electrically conductive fluid to measure even small electrical changes of a single AP, using amplification - techniques involving large electrodes are placed outside the skull; measure electric activity of large groups of neurons - magnetoencephalography: measures the changes in magnetic fields that accompany APs in the cerebral cortex provide substantial evidence of changes in cerebreal cortex Measuring the Brain’s Chemical Activity - microdialysis: collects solutions surrounding the brain‟s neurons for subsequent chemical analysis; detects amounts of specific neurotransmitters that escape from synaptic cleft a set of concentric tubes are used to circulate a carrier fluid into and out of the brain neurotransmitters and similar secretions are carries through this current, collected, and analyzed - neurochemical methods also detect chemical processes in the brain some of these methods detect chemicals by mimicking things in our body ie. when foreign protein enters body, immune system produces antibodies, that chemically attach to the protein synthetic antibodies can be produced, using chemical dye, the presence of neurotransmitters and enzymes that create them can be detected Measuring the Brain’s Neural Activity - methods developed to measure neural activity as the brain performs a function - methods combine knowledge of brain‟s physiology and visualization technology - functional MRI: (version of MRI) measures recovery times of blood hemoglobin - PET scans: measure biochemical processes in the brain to trace neurotransmitter substances - (fMRI-> oxygen levels; PET-> trace neurotransmitters) Stimulating the Brain‟s Activity - useful to look at the effects of activating regions of the brain through stimulation - moderate currents sent through an electrode, mimic an AP and activate neurons to observe how the artificial stimulation affects behavior - ex. rat presses on a lever that turns on a stimulator, sending brief pulse of electricity through an electrode in rat‟s brain Olds and Milner found if tip of the electrode is located in certain parts of the brain, animal will keep wanting to press the lever showis these parts of the brain have something to do with reward mechanisms fMRI study of male student found the same part of the brain as the rat study to be activated when images of beautiful women presented to men - transcranial magnetic stimulation: direct stimulation of the cerebral cortex induced by magnetic fields placed on scalp technique is valueable as it can be used on conscious humans who can then describe their experience method is an example of non-invasive methods of stimulation Understanding the Limitation of Brain Methods - ex. fMRI results depend on assumption that deoxygenated hemoglobin reflects neural activity; we should keep in mind other qualifications when we hear reports about such methods: 1) are all the factors controlled? this is important because we are comparing the scan of a person performing a task to that of a person performing a controlled task 2) are there any confounds? there may be another confounding factor the brain is so complex that there may be many confounding factors; modules within the brain are highly interconnected, with many feedback loops 3) can we really generalize this finding? what we find is specific for certain tasks, and we may not be able to apply to the world ex. the Mozart effect was too quickly generalized Control of Behavior - brain has 3 roles: controlling movements of muscles processing/retaining information about environment regulating physiological functions of the body- - first 2 roles have to do with outward things, the 3rd with inward things - psychology focus mostly on the outward roles-> has to do with behaviour Organization of the Cerebral Cortex - cerebral cortex contains a large groove called the central fissure, gives dividing line for the anterior (front) and posterior (back) regions - cerebral cortex is divided into 4 lobes: frontal lobe: front portion (including Broca‟s speech area and the motor cortex) damage in the frontal lobe impairs movement, planning, flexibility parietal lobe: located behind the frontal lobe and above the temporal lobe, contains the somatosensory cortex involved with spatial perception and memory temporal lobe: below the frontal and parietal lobes, contains the auditory cortex occipital lobe: the rearmost portion, contains the primary visual cortex Regions of Primary Sensory and Motor Cortex - 5 senses: vision, audition, olfaction, gestation, somatosenses - 3 parts of the cerebral cortex that receive information from the sensory organs: primary visual cortex (sight): receives visual information, located in the occipital lobes primary auditory cortex (hearing): receives auditory information, located in the temporal lobes (on the inner surface of a deep fissure) primary somatosensory cortex (touch): receives information from the body senses (touch,pressure, vibration, pain, temperature), located in the front part of the parietal lobes it‟s a vertical strip the base of the somatosensory cortex receives info about taste - for these primary sensory cortexes: left side gets information from right side of the body, and vice versa - connection between the sensory organs and the cerebral cortex are contralateral - contralateral: residing in the side of the body opposite the reference point - the part of the cerebral cortex that is most involved with movement is the primary motor cortex primary motor cortex: directly controls the movements of the body; located posterior to the frontal lobes note that motor refers to movement neurons go from parts of the primary motor cortex to muscles all over the body here, the connections are also contralateral ex. stimulate “hand region” in left primary motor cortex and right hand will move Association Cortex - cerebral cortex contains primary sensory cortex and primary motor cortex, rest of the cerebral cortex has to do with what happens between sensation and action: perceiving, learning, remembering, planning, acting anterior region: movement-related activities like planning and executing behaviors posterior region: perceiving and learning - primary sensory areas of the cerebral cortex sends info to the sensory association cortex where the info is analyzed (perception takes place here and memories are stored here) - regions close to a primary sensory area receives info only from there ex. the region of the sensory association cortex closest to the primary visual cortex gets information only from that one sensory system regions that are far away from primary sensory areas can receive info from more than onesensory system, they can integrate info from many sensory systems- - anterior part of the fr
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