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Chapter 5

PSYC 211 Chapter Notes - Chapter 5: Transcranial Magnetic Stimulation, Electromagnet, Heredity

Course Code
PSYC 211
Yogita Chudasama

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PSYC211 Chapter 5 Notes
Experimental Ablation: The removal or destruction of a portion of the brain of a laboratory animal;
presumably, the functions that can no longer be performed are the ones the region previously
Lesion Study: A synonym for experimental ablation
Excitotoxic Lesion: A brain lesion produced by intracerebral injection of an excitatory animo acid,
such as kainic acid
Sham Lesion: A placebo procedure that duplicates all the steps of producing a brain lesion except the
one that actually causes the brain damage
Stereotaxic Surgery: Brain surgery using a stereotaxic apparatus to position an electrode or cannula
in a specified position of the brain
Bregma: The junction of the sagittal and coronal sutures of the skull; often used as a reference point
for stereotaxic brain surgery
Stereotaxic Atlas: A collection of drawings of sections of the brain of a particular animal with
measurements that provide coordinates for stereotaxic surgery
Stereotaxic Apparatus: A device that permits a surgeon to position an electrode or cannula into a
specific part of the brain
Fixative: A chemical such as formalin; used to prepare and preserve body tissue
Formalin: The aqueous solution of formaldehyde gas; the most commonly used tissue fixative
Perfusion: The process by which an animal’s blood is replaced by a fluid such as a saline solution or a
fixative in preparing the brain for histological examination
Microtome: An instrument that produces very thin slices of body tissues
Transmission Electron Microscope: A microscope that passes a focused beam of electrons through
thin slices of tissue to reveal extremely small details
Scanning Electron Microscope: A microscope that provides three-dimensional information about the
shape of the surface of a small object by scanning the object with a thin beam of electrons
Confocal Laser Scanning Microscope: A microscope that provides high-resolution images of various
depths of thick tissue that contains fluorescent molecules by scanning the tissue with light from a laser
Anterograde Labeling Method: A histological method that labels the axons and terminal buttons of
neurons whose cell bodies are located in a particular region
PHA-L: Phaseolus vulgaris leukoagglutinin; a protein derived from kidney beans and used as an
anterograde tracer; taken up by dendrites and cell bodies and carried to the ends of the axons
Immunocytochemical Method: A histological method that uses radioactive antibodies or antibodies
bound with a dye molecule to indicate the presence of particular proteins of peptides
Retrograde Labeling Method: A histological method that labels cell bodies that give rise to a terminal
buttons that forms synapses with cells in a particular region
Fluorogold: A dye that serves as a retrograde label; taken up by terminal buttons and carried back to
the cell bodies
Pseudorabies Virus: A weakened form of a pig herpes virus used for retrograde transneuronal
tracing, which labels a series of neurons that are interconnected synaptically

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Herpes Simplex Virus: A form of herpes virus used for anterograde transneuronal tracing, which
labels a series of neurons that are interconnected synaptically
Computerized Tomography (CT): The use of a device that employs a computer to analyze data
obtained by a scanning beam of X-rays to produce a two-dimensional picture of a “slice” through the
Magnetic Resonance Imaging (MRI): A technique whereby the interior of the body can be accurately
imaged; involves the interaction between radio waves and a strong magnetic field
Diffusion Tensor Imaging (DTI): An imaging method that uses a modified MRI scanner to reveal
bundles of myelinated axons in the living human brain
Microelectrode: A very fine electrode, generally used to record activity of individual neurons
Single-Unit Recording: Recording of the electrical activity of a single neuron
Macroelectrode: An electrode used to record the electrical activity of large numbers of neurons in a
particular region of the brain; much larger than a microelectrode
Electroencephalogram (EEG): An electrical brain potential recorded by placing electrodes on in the
Magnetoencephalography: A procedure that detects group of synchronously activated neurons by
means of the magnetic field induced by their electrical activity; uses an array of superconducting
quantum interference devices or SQUIDs
2-deoxyglucose (2-DG): A sugar that enters cells along with glucose but is not metabolized
Autoradiography: A procedure that locates radioactive substances in a slice of tissue; the radiation
exposes a photographic emulsion or a piece of film that covers the tissue
Fos: A protein produced in the nucleus of a neuron in response to synaptic stimulation
Functional Imaging: A computerized method of detecting metabolic or chemical changes in particular
regions of the brain
Positron Emission Tomography (PET): A functional imaging method that reveals the localization of a
radioactive tracer in a living brain
Functional MRI (fMRI): A functional imaging method; a modification of the MRI procedure that permits
the measurement of regional metabolism in the brian, usually detecting changes in blood oxygen level
Transcranial Magnetic Stimulation: Stimulation of the cerebral cortex by means of magnetic fields
produced by passing pulses of electricity through a coil of wire placed next to the skull; interferes with
the functions of brain region that is stimulated
In Situ Hybridization: The production of RNA that is complementary to a particular messenger RNA in
order to detect the presence of the messenger RNA
Microdialysis: A procedure for analyzing chemicals present in the interstitial fluid through a small
piece of tubing made of a semipermeable membrane that is implanted in the brain
Targeted Mutation: A mutated gene (also called a “knockout gene”) produced in the laboratory and
inserted into the chromosomes of mice; fails to produce a functional protein
Antisense Oligonucleotide: Modified strand of RNA or DNA that binds with a specific molecule of
mRNA and prevents it from producing its protein
Methods and Strategies of Research:
The best conclusions about the physiology of behaviour are made not by any single experiment, but
by a program of research that enables us to compare the results of studies that approach the
problem with different methods

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Experimental Ablation:
Experimental ablation is one of the most important research methods used to investigate brain
functions by destroying part of the brain and evaluating the animal’s subsequent behaviour
In most cases, it does not involve the removal brain tissue but rather to destroy some tissue and
leave it in its place
Evaluating the Behavioural Effects of Brain Damage:
A lesion is a wound or injury
A researcher who destroys a part of the brain calls this a brain lesion
Lesion studies are where a part of an animal’s brain is destroyed to observe its subsequent
functions. The rationale for lesion studies is that the function of an area of the brain can be inferred
from the behaviours that the animal can no longer perform after the lesion
The distinction between brain function and behaviour is important. Circuits within the brain perform
functions, not behaviours
Each part of the brain performs a function (or a set of functions) that contributes to performance of
the behaviour
The interpretation of lesion studies is complicated by the fact that all regions of the brain are
interconnected; thus, the functions we are interested in may actually be performed by neural circuits
located elsewhere in the brain. Damage to structure X may simply interfere with the normal
operation of the neural circuits in structure Y
Producing Brain Lesions:
We typically accomplish tissue removal by sucking away brain tissue with a vacuum pump attached
to the pipette
Brain lesions of subcortical regions (regions located beneath the cortex) are usually produced by
passing electrical current through a stainless steel wire that is coated with an insulating varnish
except for the very tip. We guide the wire stereotaxically so that its end reaches the appropriate
location. Then we turn on a lesion-making device, which produces radio frequency which heats up
and destroys that brain region
Lesions produced by RF currents destroy everything in the vicinity of the electrode tip, including
neural cell bodies and the axons of neurons that pass through the region
A more selective method of producing brain lesions employs an excitatory amino acid such as
kainic acid, which kills neurons by stimulating them to death. These are referred to as excitotoxic
lesions. These lesions destroy neural cell bodies in the vicinity but spares axons that belong to
different neurons that happen to pass nearby
The selectivity of excitotoxic lesions permits investigators to determine whether the behavioural
effects of destroying a particular brain structure are caused by the death of neurons located there or
by the destruction of axons that pass nearby
When we produce subcortical lesions by passing RF currents through an electrode or infusing a
chemical through a cannula, we always cause additional damage to the brain because to get to our
target, we inevitably cause a small amount of damage even before turning on the lesion maker or
starting the infusion
Sham lesions are used as control method to see whether just the initial damage to the brain,
without applying the actually lesion method will affect the functions
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