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Chapter 5

Chapter 5 Summary - The Research Methods of Biopsychology .docx

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University of Guelph
PSYC 2410
Boyer Winters

PSYC*2410 – Behavioural Neuroscience Chapter 5 Summary The Research Methods of Biopsychology - Two major parts of this chapter: one deals with methods of studying the nervous systems and the other deals with methods of studying behaviour - Keep in mind that most of the methods that area used to study the human brain are used for clinical purpose, for either diagnoses or treatment The Ironic Case of Professor P. - Behavioural neuroscientist who went into the hospital for tests before his brain surgery - Had a brain tumor on his right auditory-vestibular cranial nerve that had to be excised (cut off) - Auditory abilities assessed by measuring ability to detect sounds then by measuring magnitude of the EEG signals evoked in his auditory cortex by clicks in his right ear - Vestibular function (balance) tested by injecting cold water into ear - He did not feel any different until the water was so cold that most people would have been on their knees, puking - Meant hearing in right ear was poor and right vestibular nerve was barely functioning - One last test to establish baseline for surgery because if something wrong was cut the right side of his face would sag - Nurse gives needle - Professor did not regain consciousness for several days and when he did he was incapable of talking, eating or even breathing  This case demonstrates that many of the research methods of biopsychology are also used in clinical settings PART ONE: METHODS OF STUDYING THE NERVOUS SYSTEM Methods of Visualizing and Simulation the Living Human Brain - Prior to the early 1970’s biopsychology was impeded by the inability to obtain images of the organ of primary interest: the living human brain - Conventional X-ray photography is useless for this purpose because it is only able to distinguish between structure that differ substantially from their surrounds (ex. a gun in a suitcase filled with clothes or a bone in flesh) - The many overlapping structures of the brain only differ slightly in their ability to absorb the radiation and therefore the X-ray would carry very little information about the shape of the individual structure it has passed through Contrast X-Rays - Useful for visualizing the brain - Contrast x-ray techniques  involve injecting into one compartment of the body a substance that absorbs x-rays either less than or more than the surrounding tissue; the injected substance then heightens the contrast between the compartment and the surrounding tissue during x-ray photography - Cerebral angiography  a contrast x-ray technique for visualizing the cerebral circulatory system by infusing a radio-translucent dye into a cerebral artery o Most useful for localizing vascular damage, but the displacement of blood vessels from their normal position can also indicate the location of a tumor X-Ray Computed Technology - Computed tomography (CT)  a computer assisted x-ray procedure that can be used to visualize the brain and other internal structures of the living body o Revolutionized the study of the human brain in the early 1970’s - During cerebral computer tomography o The patient lies with their head in the center of a large cylinder o X-ray tube on one side that projects an x-ray beam through the head to the x-ray detector on the other side o Both automatically rotate around the head, taking several x-ray photographs that are combined by a computer to generate a horizontal section of the brain o Then they are moved down to another level of the patient’s brain and the process is repeated 8 or 9 times o All 8-9 scanned horizontal brain sections are combined to provide a 3D representation of the brain - Success of CT lead to the development of other techniques (ex. MRI) Magnetic Resonance Imaging - Magnet Resonance Imagining (MRI)  a procedure in which high-resolution images are constructed from the measurement of waves that hydrogen atoms emit when they are active by radio-frequency waves in a magnetic field o Clearer brain images than CT o High spatial resolution  the ability to detect difference in spatial location o Produces 2D and 3D images Positron Emission Tomography - Positron Emission Tomography (PET)  a brain-imaging technique that has been widely used in biopsychology research because it provides images of brain activity rather than brain structure; usually by measuring the accumulation of radioactive 2-deoxyglucose (2-DG) or radioactive water in the various areas of the brain - One common version of PET: o 2-DG injected into patient’s carotid artery (artery in the neck that feeds the ipsilateral cerebral hemisphere)  2-DG is similar to glucose so will be rapidly taken up by active cells, but does not metabolize so will accumulate in active cells until it is slowly broken down o PET scan is an image of radioactivity (indicated by colour coding) in various parts of one horizontal level of the brain  If PET scan taken of patient who engages in reading for 30 seconds after 2-DG injection than the areas of the brain that were most active will be shown on the scan - Usually different levels of the brain are scanned so that the extent of brain activity can be better assessed Functional MRI - Functional MRI (fMRI)  produce images of the increase in oxygen flow in the blood to active areas of the brain - Possible because of two attributes of oxygenated blood: o 1. Active areas of the brain take up more oxygenated blood than need for their energy requirements and therefore oxygenated blood accumulates in active areas o 2. Oxygenated blood has magnetic properties (because oxygen influences the effect of magnetic fields on iron in the blood)  BOLD signal  a blood-oxygen-level-dependent (BOLD) signal, which is recorded by fMRI and is related to the level of neural firing - Four advantages over PET: o Nothing has to be injected into subject o Provides both functional and structure information in the same image o Higher spatial resolution o Used to produce 3D images of activity of the entire brain Magnetoencephalography - Magnetoencephalography (MEG)  a technique for recording changes produced in magnetic fields on the surface of the scalp by changes in underlying patterns of neural activity o Used to monitor brain activity o Major advantage: high temporal resolution  ability of a recording technique to detect differences in time (ie. to pinpoint when an event occurred)  It can record fast changes in neural activity Brain-Image Archives - Brain-Image Archive  contains the raw data collected in a particular study o Other research use archives in access the raw data and compare those data to, or combine them with, their own o Published studies only contain a few summary images in each research paper which makes it virtually impossible for researchers to compare the results to their own findings which is why brain-image archives are beneficial Transcranial Magnetic Stimulation - PET, fMRI and MEG can all create images of brain activity but they can only show correlation, not causation - Transcranial Magnetic Stimulation provides casual relations between cortical activity and psychological phenomena - Transcranial Magnetic Stimulation (TMS)  technique for disrupting the activity in an area of the cortex by creating a magnetic field under a coil positioned next to the skull; the effect of the disruption on cognition is assessed to clarify the function of the affected area of cortex o Magnetic stimulation temporarily turns off part of the brain while effects assessed o Employed to circumvent (get around) the difficultly that brain-imaging studies have in determine causation Recording Human Psychological Activity - This section deals with psychological recording methods  methods of recording physiological activity from the surface of the human body - Five Described: o 1 measure of brain activity  scalp EEG o 2 measures of somatic nervous system activity  muscle tension and eye movement o 2 measures of autonomic nervous system  skin conductance and cardiovascular activity Scalp Electroencephalography (EEG) - Measure of gross electrical brain activity - Recorded through large electrodes by a device called an electroencephalograph (EEG machine) and the technique is called electroencephalography  a technique for recording the gross electrical activity of the brain through disk-shaped electrodes (about half the size of a dime), which in humans are usually taped to the surface of the scalp - Scalp EEG reflects the sum of electrical events through the head including action potentials, postsynaptic potentials and electrical signals from the skin, muscles, blood and eyes - Some EEG waves are associated with particular states of consciousness (ex. aroused, relaxed, asleep, deep sleep – see Fig. 5.8 on pg. 107) o For example: Alpha waves  regular 8-12-per-second, high amplitude waves that are associated with relaxed wakefulness or just before falling asleep - EEG signals decrease in amplitude as they spread from their source so a comparison of signals can indicate the origin of particular waves o This is why EEG activity is often recorded from many sites simultaneously - Psychologist more interested in event related potentials (ERPs) than the background EEG signal o ERPs  the EEG waves that regularly accompany certain psychological events  One commonly studied type of event related potential is the sensory evoked potential  the change in the cortical EEG signal that is elicited by the momentary presentation of a sensory stimulus  Can be difficult to detect because noise often masks the sensory potential (ex. like detecting a whisper at a rock concert) o Signal – part of any recording that is of interest o Noise – part that’s not o Signal averaging  a method used to reduce the noise of the background  Take persons response to a stimulus (ex. a click) at the exact time the stimulus starts - say 1000 times - then averages the millivolt value of the responses  Then takes the response to a stimulus 1 millisecond (msec) from its start, 1000 times and averages these values  Repeats for 2msec, 3msec, 4msec, etc. and averages the responses for each  When these averages are plotted, the average response evoked by the click is more apparent because random background EEG is canceled out by the averaging o The analysis of average evoked potentials (AEPs) focuses on the various waves in the averaged signal  Each wave characterized by its direction, positive or negative and its latency o May also see small waves in the first few seconds after the stimulus that are not influenced by the meaning of the stimulus for the subject; these are called far-field potentials  EEG signals recorded in attenuated form at the scalp because they originate far away – for example, in the brain stem - Initially EEG scored high on temporal resolution but failed at spatial resolution - Newer techniques can accurately locate the source of signals which allows them to be colour- coded and plotted on the surface of a 3D MRI scan Muscle Tension - Muscles fibres contract in an all-or-none fashion - When you are relaxed, a few fibres in each resting muscle are contracting to keep the muscle tension - “Tense” or anxious people – high resting levels of muscle tension - Interested in this measure because it is an indication of psychological arousal - Electromyography  the usual procedure for measuring muscles tension by recording the gross electrical discharges of muscles o Two electrodes taped to the surface of skin over the muscle of interest - Electromyogram (EMG)  resulting record of raw data o Usually raw data from this converted into a more workable form and the integrated signed (ex. the total EMG activity per unit of time) is plotted which results in a smooth curve on a graph (see. Pg. 109 for a diagram) Eye Movement - Electrooculography  technique for recording eye movement - Electrooculogram (EOG)  resulting record - Horizontal movements – measured with two electrodes placed on either side of eye - Vertical – one electrode above and one below the eye - The is a steady potential different between the front (positive) and back (negative) of the eyeball which allows the change in potentials to be recorded in this technique Skin Conductance - Emotional thoughts and experiences associated with increase in the skin’s ability to conduct electricity - Skin conductance level (SCL)  the steady level of skin conductance associated with a particular situation - Skin conductance response (SCR)  the transient change in skin conductance associated with a brief experience - Thought that sweat glands are a big part of this as they tend to become active in emotional situation – especially those in the hands, feet, armpits and forehead Cardiovascular Activity - Two parts: blood vessel and heart - Relationship between cardiovascular activity and emotions o Ex. white with fear, blushing bride Heart Rate - Electrocardiogram (ECG)  recording of electrical signal that is associated with each heart beat through electrodes places the chest - Average resting heart rate of healthy adult – 70 beats/minute Blood Pressure - Two measures: o Systoles – peak pressure during heart contractions o Diastoles – minimum pressure during periods of relaxation  Expressed as systoles/diastoles in millimetres of mercury (mmHg) - Average resting blood pressure of an adult – 130/70 mmHg - Hypertension – 140/90 mmHg  serious health hazard - Sphygmomanometer – cuff that measures blood pressure Blood Pressure - Plethysmography  various techniques for measuring changes in the volume of blood in a particular part of the body o Ex. genitals during sex - Two possible methods: o Wrap gauge around target organ  Works for fingers or similarly shaped organs o Shine light through target tissue  More blood there is = more light absorbed Invasive Physiological Research Methods - More direct techniques - Often used on laboratory animals - 3 categories: lesion methods, electrical stimulation, invasive recording methods - But first: Stereotaxic Surgery - Means by which experimental devices are precisely positioned in the depths of the brain - Two things required: o Stereotaxic atlas a series of maps representing the 3D structure of the brain that is used to determine coordinates for stereotaxic surgery  Bregma – the point on the top of the skull where two of the major sutures (seams of the skull) intersect – often used as a reference point in rat atlases o Stereotaxic instrument  a device for performing stereotaxic surgery, composed of two parts: a head holder and an electrode holder (holds device to be inserted)  Electrode holder can be moved for precision in 3 dimensions:  Posterior-anterior  Dorsal-ventral  Lateral-medial Lesion Methods - A part of the brain is removed, damaged or destroyed - Behaviour assessed to determine function of lesioned structure - Four types: o Aspiration Lesions  tissue is drawn off by suction through the fine tip of a glass pipette  Used when lesions needs to be made in area of the cortical tissue that is accessible to the eyes and instrument of the surgeon o Radio-Frequency Lesions  lesions made by from the heat of a radio(high)-frequency current through the target tissue from the top of a stereotaxically positioned electrode  Lesion’s size and shape determined by current’s intensity and duration o Knife Cuts  sectioning (cutting) is used to eliminate conduction in a nerve or tract o Cryogenic Blockade (aka. reversible lesions)  the temporary elimination of neural activity in an area of the brain by cooling the area with a cryoprobe until neurons stop firing  No structural damage  Can also be produced with microinjections into the brain of local anesthetics such as lidocaine - Interpreting Lesion Effects o Cannot completely destroy a structure without producing significant damage to adjacent structures o Therefore, be cautious when interpreting lesions or you may incorrectly:  Attribute all the behaviours to the lesioned structure  Assume the lesioned structure is only responsible for the behaviours observed (even if you didn’t destroy it all) - Bilateral and unilateral Lesions o General principle, with exceptions:  The behavioural effects of unilateral lesions (restricted to one have of the brain) are much milder than bilateral lesions (involving both sides of the brain) o Most experimental studies of lesion effects  bilateral Electrical Stimulation - Delivered across the two tips of a bipolar electrode – two insulated wires wound tightly together and cut at the end - Weak pulses of current produced an immediate increase in the firing of neurons near the tip of the electrode - Particular behaviour response depends on: electrode location, parameters of the current and the test environment in which the stimulation is administered Invasive Electrophysiological Recording Methods - Four methods: o Intracellular Unit Recording  provides a moment-to-moment record of the graded fluctuations in one neuron’s membrane potential  Performed on chemically immobilized animals o Extracellular Unit Recording  provides a record of the firing of a neuron from the extracellular fluid next to it but no information about the neuron’s membrane potential  Originally done on one neuron, but now up to 100 simultaneously in the same general area o Multiple Unit Recording  graph of the total number of recorded action potentials per unit of time  Larger tip that picks up signal from many neurons and slight change in position due to movement of the subject has little overall effect o Invasive EEG Recording  EEG signals recorded though large implanted electrodes rather than through scalp electrodes  Cortical EEG – recorded through stainless steel skull screws  Subcortical EEG – recorded through stereotaxically implanted wire electrodes Pharmacological Research Methods - Manipulate and record the brain using chemical methods - Drugs that increase or decrease the effects of a particular neurotransmitter and observe the behavioural consequences Routes of Drug Administration - Orally  fed - Intragastrically  injected though tube into the stomach - Intraperitoneally (IP)  injected hypodermically into the peritoneal cavity of the abdomen - Intramuscularly (IM)  into a large muscle - Subcutaneously (SC)  into the fatty tissue beneath the skin - Intravenously (IV)  into a large surface vein ** Problem with all these peripheral routes: many drugs do not readily pass through the Blood Brain Barrier (BBB) **Solution: - Cannula drugs administered through a fine, hollow tube that has been stereotaxically implanted into the brain Selective Chemical Lesions - More selective lesions created by inserting neurotoxins (neural poisons) that have an affinity for certain component of the nervous system o Ex. kainic acid or ibotenic acid  taken up by cell bodies at the tip of the cannula o Ex. 6-hydroxy-dopamine (6-OHDA)  taken up by neurons that release neurotransmitter norepinephrine or dopamine Measuring Chemical Activity of the Brain - The 2-Deoxyglucose (2-DG) Technique o Animal given radioactive 2DG (similar to glucose – see PET section above) o Engages in behaviour of interest o Killed – brain removed and sliced o Slices subjected to autoradiography  the technique of photographically developing brain slices that have been exposed to radioactively labelled substance such as 2DG so that regions of high uptake are visible (show up as black spots) - Cerebral Dialysis o Cerebral Dialysis  a method of
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