Chapter 5 - Research Methods of Biopsychology

Contrast X-Ray Technique

Injects a substance that absorbs x-rays either less than or more than the surrounding tissue into one compartment of the body

-Heights the contrast between the compartment and surrounding tissue during the X-ray

Cerebral Angiography - Infusion of radio-opaque dye into a cerebral artery to visualize cerebral circulatory system

-Help locate vascular damage, displacement of blood vessels indicating tumors

Computed Tomography (CT)

Visualizes the brain and other internal structures of the body by producing 3d images

-X-ray tube projects an X-ray beam and rotates around the head of the patient, images are them combined by a computer to generate a scan of one horizontal section

-Tube and detector are moved along the axis of the patient’s body to scan the next level, etc

Positron Emission Tomography (PET)

Provides images of brain activity rather than brain structure

-Radioactive fluorodeoxyglucose (FDG) is injected into the carotid artery, rapidly up taken by cells and accumulates in active neurons and astrocytes as its gradually broken down

-Resulting scan indicates areas of the target brain level most active

-Can also identify distribution of molecules by injecting radioactively labeled ligands (ions, molecules) and documenting distribution

Magnetic Resonance Imaging (MRI)

Structure 3D brain-imaging procedure

-Different brain structures have different amounts of water, therefore radio-frequency waves emitted by a particular brain structure are different from its neighboring brain structure

-Provides high spatial resolution - ability to detect and represent differences in spatial location

Diffusion Tensor MRI

New MRI technique, identifies pathways along which water molecules rapidly diffuse (identifies the major tracts in the brain)

-Helps understand connections of structures (the connectome)

Functional MRI (fMRI)

Produces images representing increase in oxygenated blood flow to active areas of the brain

-Active areas of the brain take up more oxygenated blood and oxygenated blood has different magnetic properties, this allows active areas of the brain to be identified

-fMRI records the BOLD signal (blood-oxygen-level-dependent signal)

BOLD Signal - indicates parts of the brain that are active/inactive during a cognitive/behavioural test

Advantages of fMRI over PET

1. No injections required

2. Provides structure/functional information in the same image

3. Spatial resolution is better

Functional Ultrasound Imaging (fUS)

Uses ultrasounds (sound waves of a higher frequency than we can hear) to measure changes in blood volume in certain brain regions

-More activity = blood levels increase = alters passage of the ultrasound

Advantages of fUS over fMRI and PET

1. Cheaper

2. Portable

3. Can be used for imaging individuals unable to undergo PET or fMRI (infants)

Transcranial Magnetic Stimulation (TMS)

Used to turn off an area of human cortex by creating a magnetic field

-Magnetic stimulation turns off part of the brain while effects of disruption on cognition and behaviour are assessed

-Used to circumvent difficulty of brain-imaging

Transcranial Electrical Stimulation (TES)

Technique used to stimulate an area of the cortex by applying an electrical current through electrodes placed directly on the scalp

-Electric stimulation temporary increases activity in the brain region

-Controversial (may have detrimental effects)

Transcranial Ultrasound Stimulation (tUS)

Used to activate particular brain structures, able to active subcortical structures unlike TMS and TES (can only activate cortex)

-Used to make small permanent lesions to a brain structure, can treat several conditions without requiring surgery

Scalp Electroencephalography (EEG)

Measure of gross electrical activity of the brain, using large electrodes attached to the scalp

-Reflects the sum of electrical events in the head (APs, PSPs, signals from skin, muscles, blood, eyes, etc)

-Does not provide unclouded view of neural activity, but certain EEG wave forms are associated with particular stats of consciousness/cerebral pathology

Alpha Wave - Regular, 8-12 second high amplitude waves associate with relaxed wakefulness

Event Related Potentials (ERPs)

EEG waves that accompany certain psychological events

-Sensory Evoked Potential - change in cortical EEG signal elicited by momentary presentation of a sensory stimulus

-Has two components; response to the stimulus (the signal) and background EEG activity (the noise)

-Signal is part of any recording of interest, noise is not of interest

-Signal Averaging - reduces background noise by increasing signal-to-noise ratio

Average Evoked Potentials Analysis

Focuses on various waves in the averaged signal

-P300 wave - positive wave that occurs 300 milliseconds after a momentary stimulus that has meaning for the participant

-Far-Field Potentials - EEG signals recorded in attenuated form at the scalp because they originate far away from the region

Magnetoencephalography (MEG)

Measures changes in magnetic fields on the surface of the scalp that are produced by canges in underlying patterns of neural activity

Advantages of MEG over EEG

1. Better spatial resolution than EEG (can localize changes in electrical activity int he cortex with more precision)

2. Can localize subcortical activity with greater reliability than EEG

Electromyography

Measures muscle tension, EMG activity recorded between two electrodes on the surface of the skin over the muscle of interest

-Increase in raw EMG signal indicates increase in muscle contraction

-Raw signal is fed into a computer that calculates total amount of EMG spiking per unit of time (intervals), resulting in a smooth curve

Electrooculography

Records eye movements based on the fact that a steady potential difference exists between the front (positive) and back (negative) of the eyeball

-When eye moves, electrical potential change is recorded by electrodes on either sides of the eye

-Horizontal and vertical movements both recorded

Skin Conductance Response and LEVEL (SCR,SCL)

SCL - Measure of background level of skin conductance associated with particular situations

SCR - Measure of transient changes in skin conductance associated with discrete experiences

SCL/SCR measure sweat glands as they become active in emotional situations

Electrocardiogram

Electrocardiogram - Records the electrical signal associated with each heartbeat, resting rate is 70bpm

-One way of recording cardiovascular activity

Blood Pressure - Sphygmomanometer

Arterial blood pressure measured by the peak pressure during periods of heart contraction (systoles) and measurement of minimum pressure during periods of relaxation (diastoles)

-Expressed ratio of systolic over diastolic in mmHG

-Normal pressure is 130/70 mmHG, more than 140/90 mmHG = hypertension

Plethysmography

Various techniques for measuring changes in the volume of blood in particular locations

-Can be measured by wrapping a strain gauge or by shining light under tissue and measuring amount of light absorbed