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Chapter 5

Chapter 5.pdf

6 Pages

Course Code
Psychology 2220A/B
Scott Mac Dougall- Shackleton

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TheResearch Methodsof Biopsychology January-12-12 12:00PM  PARTONE:METHODSOFSTUDYINGTHENERVOUSSYSTEM METHODS OFVISUALIZING AND STIMULATING THE LIVING BRAIN - X-raysare useless in obtaining images of the human brain ○ Xray photography isonly effective in characterizing internal structures that differ substantially from their surroundings in the degree to which they absorb X rays ○ Butby the time an x ray beam has passed through the numerous overlapping structures of the brain (which differ only slightly), it carries littleinformation about the structures through which it has passed - CONTRAST X-RAYS - ContrastX-raytechniques - involve injecting into one compartment of the body a substance that absorbs X-rays either less than or more than thesurrounding tissue ○ The injected substance then heightens the contrast between the compartment and the surrounding tissue during X-ray photography - Cerebralangiography - a type of contrast x-ray technique that uses the infusion of a radio-opaque dye into a cerebral artery to visualize the cerebral circulatory system during x-ray photography ○ Mostuseful fore localizing vascular damage - X-RAY COMPUTED TOMOGRAPHY - Computedtomography (CT) - a computer assisted x-ray procedure that can be used to visualize the brain and other internal structures of the livingbody - AkaCAT scan - Usuallyobtains scans of 8 or 9 horizontal brain sections - Provide a 3D representation - MAGNETIC RESONANCE IMAGING (MRI) - Magneticresonance imaging (MRI) - a procedure in which high-res images are constructed from the measurement of waves that hydrogen atomsemit when they are activated by radio-frequency waves in a magnetic field - Providesclearer images o the brain than a CT - Spatialresolution - the ability to detect and represent differences in spatial location - Produces 3D images - The stronger the magnetic field, the higher the resolution 1.5 tesla - 3 tesla - used for human research - 60000Xearth's mag field - POSITRONEMISSION TOMOGRAPHY (PET) - Positronemissiontomography (PET) - the first brain imaging technique to provide images of brain activity (functional brain images) rather thanimages of brain structure (structural brain images) - Commonversion of PET - radioactive 2-deoxyglucose (2-DG) isinjected into the patient's carotid artery (an artery of the neck that feeds the ipsilateral cerebral hemisphere) ○ Due to its similarityto glucose, 2-DG is rapidly taken up by active, energy-consuming cells ○ 2-DG cannot be metabolized - so it accumulates in active neurons until gradually broken down - Each PET scan is an image of the levels of radioactivity in various partsof one horizontal level of the brain - will indicate the active areas of the brainafter the 2-DG injection - Notreally an image of the brain, but rather a coloured map of the amount of radioactivity in each of the tiny cubic voxels that compose the scan - Veryindirect - Shittyresolution - FUNCTIONAL MRI - Mostinfluential tool of cognitive neuroscience - FunctionalMRI (fMRI) - produce images representing the increase in oxygen flow in the blood to active areas of the brain - Possiblefor two reasons: 1. Activeareas of the brain take up more oxygenated blood than they need for their energy requirements, and thus oxygenated blood accumulates in active areas of the brain 2. Oxygenated blood has magnetic properties (oxygen influences the effect of magnetic fields on iron in the blood) - BOLD signal- the signal recorded by fMRI ○ BOLD = blood-oxygen-level-dependent ○ Increase in neural activity = increase in blood oxygen = increase in fMRI signal - Fouradvantages of fMRI over PET: 1. Nothinghas to be injected into the subject 2. Itprovides both structural and functional information in the same image 3. Itsspatial resolution isbetter 4. Itcan be used to produce 3D images of activityover the entire brain - fMRI pictures aren't pictures of human neural activity - justof the BOLD signal - Too slow to capture many neural responses ○ Takes 2 or 3seconds to create an image - and many (AP) occur in milliseconds - fMRI vsMRI... - fMRI ○ Poorer resolution ○ Manyimages - MRI ○ Goodresolution ○ One image - MAGNETOENCEPHALOGRAPHY - Magnetoencephalography (MEG) - measures changes in magnetic fields on the surface of the scalp that are produces by changes in underlying patterns of neural activity - Itsmajor advantage over fMRI is its temporal resolution - it can record fast changes is neural activity - TRANSCRANIAL MAGNETIC STIMULATION - Weakness in PET, fMRI, and magnetoencephalography - they can be used to show a correlation between brain activity and cognitive activity, butthey can't prove that the brain activity caused the cognitive activity - Transcranialmagnetic stimulation (TMS) - a technique for affecting the activity in an area of the cortex by creating a magnetic field under a coilpositioned next to the skull ○ The magnetic stimulation temporarily turnsoff part of the brain while the effects of the disruption on cognition and behaviour are assessed - TMSis often used to circumvent the difficulty that brain imaging studies have in determining causation - Impairments = temporary "virtual lesions" ○ Effects can last from msec tomin ○ Brief effects are useful for studying timing of processes in diff brain areas ○ Thought to be safe for most subjects  Someexclusions - e.g. People with epilepsy RECORDINGHUMAN PSYCHOPHYSIOLOGICAL ACTIVITY - Psychophysiologicalrecordingmethods - methods of recording physiological activityfrom the surface of the human body - SCALP ELECTROENCEPHALOGRAPHY - Electroencephalogram (EEG) - a measure of the gross electrical activity of the brain - measured with an electroencephalograph - InEEG studies of human subjects, each channel of EEG activity isusually recorded from disk shaped electrodes, about half the size of a dime, which are taped to the scalp - Alphawaves - regular, 8- to 12-per-second, high-amplitude waves that are associated with relaxed wakefulness - Can detect the origin of particular waves b/c EEG signals decrease in amplitude as they spread from their original source - why we use many sites - Event-relatedpotentials (ERPs) - EEG waves thataccompany certain psychological events ○ Sensoryevokedpotential - the change in the cortical EEG signal that is elicited by the momentary presentation of a sensory stimulus - Cortical EEG that follows a sensory stimulushas two components: ○ Signal: the response tothe stimulus  Of interest to us ○ Noise: the ongoing background EEG activity  Sometimesmasks the signal - Signalaveraging - a method used to reduce the noise of the background EEG - P300wave- the positive wave that occurs after a momentary stimulusthat has meaning for the subject - Far-fieldpotentials - smallwaves of an evoked potential in the firstfew msec's after a stimulusthat are not influences by the meaning of the stimulusfor the subject - Goodfor temporal resolution - Bad for spatial resolution - MUSCLE TENSION - Movement results when a large number of muscle fibers contract at the same time in our skeletal muscles - Electromyography - the usual procedure for measuring muscle tension ○ The resulting record iscalled an electromyogram (EMG) - recorded b/w two electrodes taped to the surface of the skin over the muscle ofinterest  Increase in muscle contraction = increase in the amplitude of the raw EMG signal - Psychologistsdon'tuse the raw signal, but rather an integrated signal - EYE MOVEMENT - Electrooculography - the electrophysiological technique for recording eye movements - the resulting record is an electrooculogram (EOG) ○ Based on the fact that there is a steady potential difference b/w the front (positive) and back (negative) of the eyeball - so when the eye moves,a change in the electrical potential b/w electrodes placed around the eye can be recorded - SKIN CONDUCTANCE - Two mostcommon indexes of electrodermal activity: ○ Skinconductance level (SCL) - a measure of the background level of skinconductance that'sassociated with a particular situation ○ Skinconductance response(SCR) - a measure of the transient changes in skinconductance that are associated with discrete experiences - Sweat glands - cool the body; active in emotional situations - CARDIOVASCULAR ACTIVITY - Two parts: blood vessels and heart - Three diff measurements of cardiovascular activityare... - Heartrate - Electrocardiogram (ECG or EKG) - records the electrical signal associated with each heartbeat through electrodes placed on the chest - Avgfor healthy heart = 70 beats per minute - Blood pressure - Measuring arterial blood pressure involves two measurements: ○ Measuring the peak pressure during the periods of heart contraction - the systoles ○ Measuring the minimum pressure during the periods of relaxation - the diastoles - BP= sys/dias(s d) in mmHg ○ Normal= 130/70for adult ○ Hypertension= anything over 140/90mmHg - Measured with a sphygmomanometer - Blood volume - Changes in blood volume in particular areas of the body are associated with psychological events - Plethysmography -measures changes of blood volume ○ More blood = more light absorption INVASIVE PHYSIOLOGICAL RESEARCH METHODS - STEREOTAXIC SURGERY - Stereotaxicsurgery - the means by which experimental devices are precisely positioned in the depths of the brain - Two things are required: ○ Stereotaxicatlas - used to locate brain structures - Brain has 3D - Reference point = bregma - the point on the top of the skull where two of the major sutures intersect ○ Stereotaxicinstrument has two parts: - Headholder - firmly holds each subject's brain in the prescribed position and orientation - Electrode holder- holds the device to be inserted □ Movesanterior-posterior, dorsal-ventral, and lateral-medial - LESION METHODS - Apart of the brain is removed, damaged, or destroyed and then the subject's behaviour is assessed to determine the functions of the lesioned structure - Foranimals and humans - Aspiration lesions - Used when a lesion is to be made in an area of cortical tissue that is accessible to the eyes and instruments of the surgeon - The cortical tissue isdrawn off by suction through a fine-tipped handheld glass pipette - Radio-frequency lesions - Make smallsubcortical lesions by passing radio frequency current (high freq) through the target tissue from the tip of a stereotaxically positioned electrode ○ Heatfrom current destroys tissue - Knife cuts - Used toeliminate conduction in a nerve or tract - Doesn't produce extensive damage to surrounding tissue - Cryogenic blockade - When coolant ispumped through an implanted cryoprobe, neurons near the tip are cooled until they stop firing - activity returns when tissue warmsup - Iteliminates the contribution of a particular area of the brain to the ongoing behaviour of the subject - Reversible lesions - so are local anaesthetics - Interpreting lesion effects - "amygdala lesions" - its effect could be due tothe damaged neighbouring structures ○ Alsonote that it doesn't mean all of the amygdala is removed - Bilateral and unilateral lesions - Unilateral lesions - lesions restricted to one half of the brain ○ Effects are much more milder than those of symmetrical bilateral lesions - lesions involving both sides of the brain - Innonhumans - Mostlesion studies are bilateral lesions - ELECTRICAL STIMULATION - Usuallydelivered across the two tipsof a bipolar electrode - two insulated wires wound tightly together and cut at the end - Hasbehavioural effects opposite to those of lesion studies ○ Eating, drinking, copulating, sleeping, etc ○ Lesioning can be used to remove, damage, or inactivate a structure ○ Electrical stimulationmay be used to"activate" a structure ○ Stimulationof a structure may have an effect opposite tothat seen when the structure islesioned - INVASIVE ELECTROPHYSIOLOGICAL RECORDING METHODS - Intracellular unit recording - measures membrane potential of a
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