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Chapter 5

PSYC 211 - Chapter 5.docx

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PSYC 211
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Chapter 5 Methods and Strategies of ResearchStory young people showing up to neurology clinics because of drug1Patients unable to speak intelligibly constantly drooled eyes open with fixed stare2All were taking a new IV drug new heroin an opiate related to meperidine Demerol3The drug was contaminated and messed with dopaminergic neurons 4All given LDopa because looked like Parkinsons and worked at first but then stopped5Used aborted human fetuses for their dopaminesecreting neurons and introduced them 6MrB was given an injection of radioactive LDOPA and then given PET scan Radioactive particles broke down7Prepare the dopaminergic neurons for implantation8Mr B was anesthetized cuts made in scapl to expose parts of the skull put stereotaxic apparatus on his skull drilled holes and made measurements guided injections into the caudate nucleus and putamen removed stereotaxic apparatus sutured incisions 9Recovered much of his motor controlthe cells survived and secreted dopamine Experimental Ablation 10Destroying part of the brain and evaluating the resulting behaviourusually the functions that can no longer be performed are the ones the region previously controlled11In most cases the researcher destroys some of the brain tissue and leaves it in place instead of removing it12Oldest method Evaluating the Behavioural Effects of Brain Damage 13Lesionwoundinjury14Lesion studyexperimental ablation15Our goal is to determine what functions are performed by different brain structures and to understand how these functions are combined to accomplish particular behaviours16Brain function is different from behaviour17A bunch of functions contribute to a behaviour18Ex reading is a behaviour which requires the functions of controlling eye movements focusing the lens and recognizing words and letters The same functions can be used in different behaviours19Researcher wants to know what functions are involved in a behaviour and what brain mechanisms control these functions20Lesion studies complicated all regions of the brain are interconnected lets say we find damage in brain structure X Damage to X impairs a certain behaviour We cant conclude that a function essential to this behaviour is attributed to structure X The functions were interested in may be performed by neural circuits located elsewhere but damage to structure X interfered maybe with the Y circuits Producing Brain Lesions 21For structures immediately beneath skull anesthetize the animal cut scalp remove skull aspirate the brain tissue suction by glass pipette on the surface of the brain and suck it with a vacuum pump attached to the pipette22Subcortical regions beneath cortex pass electrical current through stainless steel wire thats insulated with a varnish except for the tip Guide wire stereotaxically so that the end reaches the place for the lesion turn on lesionmaking device that produces radio frequency RF current of alternating high frequency passing current produces heat that kills cells in the region surrounding the tip of the electrode23Lesions produced by the wire destroy everything in vicinity of the electrode tip includes cell bodies axons of neurons that pass through24More selective lesion method excitatory amino acid like kainic acid kills neurons by stimulating them to deathexcitotoxic lesions Inject through a cannulaThis spares axons that pass by good to detect if a behaviour is due to the neurons located there or axons that pass by that region25Even more specific targeting and killing certain neurons by attaching toxic chemicals to antibodies that act on a certain protein only found in certain neurons in the brain the toxic antibodies will kill the neurons the proteins are attached to 26Sham lesionsare used as controls because when we pass an electrode or cannula through the brain want to make sure its not the small amount of damage produced by this that causes a difference in behaviour To do them you anesthetize the animal put it in stereotaxic apparatus cut open scalp drill the holes insert the electrode or cannula and lower it to the same depth We do everything but turn on the lesion marker or start the infusion27Sham lesion kind of like placebo28To temporarily disrupt the activity of a regioninject anestheticdrug called muscimol into appropriate part of the brain Blocks action potentials in axons entering or leaving the region Reversible brain lesion Inhibits GABA receptors Stereotaxic Surgery 29Used to get the tip of an electrode or cannula to a precise location deep in the animals brain30Stereotaxicsolid arrangement Locate objects in space31Stereotaxic apparatus has a holder that fixes the animals head in place carrier that moves the electrode or cannula through the measured distances in all 3 axes of spaceThe Stereotaxic Atlas 32No 2 brains of animals of a given species are completely identical but there is enough similarity among individuals to predict the location of particular brain structures relative to external features of the head33Its best to use reference points like once you find the junction of a bunch of bones like the bregmastructures are relatively in constant position relative to the bregma
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