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Chapter 5

PSYC 2410 DE S12 Textbook Notes Chapter 5

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University of Guelph
PSYC 2410
Elena Choleris

Chapter 5: The Research Methods of Biopsychology The Ironic Case of Professor P. 5.1: Methods of Visualizing and Stimulating the Living Human Brain Conventional X-ray are useless for viewing the living brain. By the time an X-ray beam has passed through neural tissue, with its numerous folds of tissue with similar ability to absorb X-Rays, there is little detail that can be seen from an x-ray Contrast X-Rays: X-Ray techniques that involve the injection into one compartment of the body a substance that absorbs X-ray either less than or more than the surrounding tissue. o CerebralAngiography: Contrast X-Ray technique uses the infusion of a radio-opaque dye into a cerebral artery to visualize the cerebral circulatory systems during X-ray photography Most useful for locating vascular damage Displacement of blood vessels from their usual position can indicate the presence of a tumour X-Ray Computed Tomography: Computer-assisted X-ray procedure that can be used to visualize the brain and other internal structures of the human body. o Discovered in the 1970's o Patient lays with their head in the center of a large cylinder o On one side of the cylinder is an X-ray tube that projects an X-ray beam through the head to an X-Ray detector mounted on the other side o Both the emitter and the recorder rotate automatically around the patient, taking many individual images. o The information from all the images are combined by the computer for a single flat image of the brain. o The procedure is then repeated until about 8 or 9 flat images have been produced. o The images combined can offer a three dimensional view of the brain Magnetic Resonance Imaging: Aprocedure in which high resolution images of structures of the living brain are constructed from the measurement of waves that hydrogen atoms emit when they are activated by radio-frequency waves in a magnetic field. o MRIs provide clearer pictures of the brain than a CT o Spatial Resolution: The ability to detect and represent differences in spacial location. o MRIs typically have relatively high spatial resolution. o Another benefit of MRIs is that they are able to produce images in three dimensions. Positron Emission Tomography: Atechnique for visualizing brain activity, usually by measuring the accumulation of 2-deoxyglucose (2-DG) or radioactive water in in the various areas of the brain. o First imaging technology to provide images of brain activity (Functional images) rather than brain structure (Structural images) o Because 2-deoxyglucose is so similar to glucose, it is taken up rapidly by active, energy- consuming cells o Unlike glucose, 2-deoxyglucose cannot be metabolized, so it accumulates in active tissues until it is gradually broken down by the body o Thus, if a pet scan were taken of a patient who engages in an activity for about 30 seconds (ie. Reading) the PET scan would show which areas of the brain were most active during the performance of the activity. o Pet scans do not show structures in the brain, and they are not really images of the brain. o APET scan is a conglomerate of colours showing which portions were the most active during the time immediately following the uptake of 2-deoxyglucose o How well the PET scan matches up to a structural brain area can only be estimated by superimposing the PET scan data on a structural image of the brain being observed. Functional MRI: Amagnetic resonance imaging technique for infering brain activity by measuring increased oxygen flow into particular areas. o fMRI has become the most influential tool used in cognitive Neuroscience, and is widely used for medical diagnosis. o fMRI is made possible by two qualities of oxyginated blood: Active areas of the brain take up more oxyginated blood than necessary, meaning that oxyginated blood accumulates in the tissues using it. Oxyginated blood has magnetic properties, oxygen influences the effect of magnetic fields on iron o BOLD Signal: Signal recorded by fMRI machines.Acronym for Blood-Oxygen Level Dependent Signal. o fMRI has four advantages over PET technology: Nothing has to be injected into the subject. It provides both functional and structural information about the brain in the same image It has improved spatial resolution compared to PET technology It can be used to produce three dimensional images of activity over the entire brain. o Disadvantages of fMRI fMRI is often misunderstood because it presents so many advantages, meaning that people will often trust studies supported by fMRI data without critically evaluating the research involved. fMRIs are not real-time images of neural activity. It does not capture electrical activity or the transfer of potentials. It measures the BOLD signal, which has a complex, variable and poorly understood relationship to neural activity in the truest sense. fMRI is too slow to capture many neural responses. It takes between 2-3 seconds for an image to be generated. Many neural activies, however, including action potentials happen on the time order scale of milliseconds. Magnetoencephalography:Atechnique for recording changes produced in magnetic fields on the surface of the scalp by changes in underlying patterns of neural activity. o Temporal Resolution: The ability to detect and represent differences in temporal location. o The major advantage of MEG imaging over fMRI is its temporal resolution, it's ability to detect and record very rapid changes in neural activity. Transcranial Magnetic Stimulation (TMS): Atechnique 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 on cognition is assessed to clarify the function of the affected region of the cortex. o The above mentioned methods for developing images of the brain are all excellent ways of seeing what is going on inside our heads, but they all share a single common weakness: Imaging techniques can be used to show correlation between brain activity and cognitive activity, but it cannot prove that brain activity is the cause of cognitive activity. 5.2: Recording Human PsychophysiologicalActivity There are five commonly used physiological methods of making inferences about the brain o EEG measures brain waves o Muscle tension measures somatic nervous system activity o Eye movement measures somatic nervous system activity o Skin conductance measures autonomic nervous system activity o Cardiovascular activity measures autonomic nervous system activity Scalp Electroencephalography o The electroencephalagram is a measure of the overall electrical activity in the brain o In EEG studies of human subjects, each channel of EEG activity is recorded through an individual electrode attached to the scalp o EEG waves from the scalp are a mixture of neural activity, including action potentials, post- synaptic potentials and electrical signals from the skin, muscles, blood and eyes o The value of EEG in research is that certain patterns of brain waves are associated with certain states of consciousness (ie. Sleeping and waking) or particular types of cerebral pathology (ie. Seizures) o Alpha Waves: regular, 8- to 12-per second, high-amplitude waves that characterize relaxed wakefulness. o EEG waves decrease in amplitude as they move farther away from their source, wo slight differences in amplitude strength can be used to determine the origin of particular waves. o Event Related Potentials: The EEG waves that typically accompany certain psychological events. Sensory-Evoked Potential: Commonly studied event related potential; Momentary change in cortical EEG readings that occurs when the individual is presented with a stimulus. Sensory-evoked potential has two components: background EEG, the portion of the EEG which is of no interest to researchers, and the signal, the portion of the EEG which is of interest to researchers Often there is so much noise captured when recording a sensory-evoked potential that the signal is difficult or impossible to detect. (The signal is masked) SignalAveraging: Amethod used to reduce the noise of background EEG and isolate the signal. Asubject's EEG scalp response is recorded for the same stimulus many times. Acomputer identifies the millivolt value of each of the stimulus traces at its starting point, and averages them out. The computer then repeats this procedure for each millisecond after the initial starting point and plots the values of these means against time. o The plotted averages show a much clearer picture of the evoked potential because the noise is cancelled out by the averaging process o Each averaged wave is characterized by its direction and its latency o The direction can be either positive or negative. By convention, positive waves are observed as downwards deflections and negative waves are observed as upwards deflections. o Latency reflects how long after the stimulus was presented that the wave occurred o P300 Wave: Positive wave that occurs approximately 300 milliseconds after
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