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Chapter 5

Chapter 5: Research

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McGill University
PSYC 211
Yogita Chudasama

Experimental Ablation/lesion study: removal/destruction of portion of brain to evaluate subsequent behavior  Evaluating behavioral effects of damage: lesion studies used to infer function of brain parts based on behavior animal can’t perform. Circuits in brain does functions, not behavior; each region does function, contributes to behavior. Interpretation complicated b/c regions interconnected; can’t conclude that function performed by neurons in X; may interfere w/ operation of circuits in Y (septum links hippocampus, disrupts maternal behavior)  Making lesions: electric current passed through wire w/ un-insulated tip. Guide wire stereotaxically, turn on RF current, heat kills everything near tip, inc. neural cell bodies, axons nearby. Excitotoxic lesions use amino acid (kainic), stim. neurons to death, selectivedet. if behavioral effects caused by death of neurons or nearby axons. 6-HD: more specific, selectively taken up by axons/buttons of noradrenergic/ dopaminergic neurons, poison from inside. Sham lesions: placebo, duplicate all steps except actual damage. For temporary/reversible lesion: local anesthetic (blocks potentials in axons), muscimol (stim. GABA receptors, inactivates by inhibiting neurons).  Stereotaxic surgery: ability to locate objects in space. stereotaxic apparatus positions electrode/cannula o Stereotaxic atlas: photos correspond to frontal sections at distances rostral/caudal to bregma. Grid shows distances of structures ventral to top of skull, lateral to midline. No brains alike; similar enough to predict location of structure relative to external features. Skull made of bones that grow together, form sutures. Once fontanelle closes gap between coronal/sagittal sutures, creates a junction called bregma, good reference point. o Stereotaxic apparatus: positions electrode/cannula into specific part of brain. Head holder, electrode holder, calibrated mechanism can move in measured distances along 3 axes: anterior/posterior, dorsal/ventral, lateral/medial. Used for lesions, stimulate/destroy neurons, inject drugs, monitoring.  Histological methods: fix/slice/stain/examine brain to verify precise location of damage after behavior testing o Fixation/sectioning: fixative (e.g. formalin) halts autoloysis (enzymes self-dissolve), hardens, kills extra. Perfusion: replace blood w/ saline. Microtome: 10-80 μm for light microscope, <1 μm for e- microscope, inc. knife, platform, mechanism to advance for next cut. Slices put on slides, stain, mounting medium, coverslip. o Staining: see fine details. Simplest: cell-body stain: methylene blue (cresyl violet) taken up by Nissl substance (RNA, DNA, proteins). Stain not selective for neural cell bodies; stains all cells. o E- microscopy: transmission e-: passes focused beam of e- through thin slices of tissuereveal small details. Scanning e-: less magnified, but 3D, scans tissue w/ moving beam of e-. o Confocal laser scanning microscopy: details inside thick slice stained w/ fluorescent dye by scanning tissue w/ light from laser beam.  Tracing neural connections: rats w/ VMH lesions did not mate - link between VMH and rest of brain. o Tracing efferent axons: indirect pathway VMHmuscles, anterograde labeling: use chems taken by dendrites/soma, transported axonsbuttons. Lectin protein, esp. PHA-L, used to ID efferent axons. PHA-L seen on microscope w/ immunocytochemical methods: use radioactive antibodies to indicate presence of particular proteins/peptides (antigens). antigens on invading microorganism contact antibodies that recognize themtrigger attack. Antibodies made for any antigen, attached to dyes, fluorescent/brown. Rat injected w/ PHA-L into VMH, brain treated w/ PHA-L antibody attached to brown dye. o Tracing afferent axons: retrograde labeling finds inputs to VMH, labels cell bodies that give rise to buttons that form synapses w/ cells. Fluorogold taken up by buttons, carried back through axons to soma, fluoresce, show medial amygdala input to VMH. Labeling only shows 1 link in chain; transneuronal tracing shows more neurons that form synaptic connections. Pseudorabies virus: labels series of neurons that are interconnected synaptically – taken up by neurons, spreads. Labeling methods provide us w/ “wiring diagram” of brain.  Study of living human brain: computerized tomography (CT): head placed in ring w/ X-ray tube, X-ray detector opposite. X-ray beam passes through head, detector measures radioactivity, scans anglespicture. Lim. to horizontal. MRI: magnetic field (not X-rays), realigns nuclei spin. RF through bodynuclei emit own radio waves. MRI detects radiation from H, dif. concentrations in dif. tissues. Can be sagittal/frontal/horizontal plane. Recording, stimulating neural activity: brain functions involve activity of
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