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U5- research methods in biopsych.docx

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PSYC 271
Monica Valsangkar- Smyth

L5: RESEARCH METHODS IN BIOPSYCH Feb 7/12 1. Visualizing the human brain Contrast X-Rays - Involve injecting one compartment of the body a substance that absorbs X-rays either less than or more than the surrounding tissue. - Cerebral angiography uses the infusion of a radio-opaque dye into a cerebral artery to visualize the cerebral circulatory system during X-ray photography. - Usually used for localizing vascular damage but displacement of blood vessels from normal position can indicate location of a tumor. X-ray Computed Tomography - Computed tomography (CT) is a computer assisted X-ray procedure that can be used to visualize the brain and other internal structures of the living body. - The patient lies with their head in the center of a large cylinder with an X-ray tube that projects an X-ray beam through the head to an X-ray detector mounted on the other side. - The X-ray tube and detector automatically rotate, taking many individual X-ray photographs as they rotate to provide a 3D representation of the brain. Positron Emission Tomography ( PET) - When a part of the brain is active, there is more blood flow to the region - Inject patient with radioactive 2-deoxyglucose in carotid artery which is similar to glucose, so it is taken up by neurons - More active neurons take up more 2-DG but unlike glucose 2-DG can’t be metabolized - The subject is then given a task (i.e. reading). When the 2-DG decays, subatomic positrons are emitted which are detected by a scanner - The computer reconstructs variations in the density of particle flow to produce an image of a brain section - The PET scan reveals a series of horizontal sections where radioactivity has accumulated Neural responses of Prefrontal - PET scans aren’t really images of the brain, it’s a colored map of the amount of Cortex and Amygdala radioactivity. Abe et al. - Looked at roles of subregions within the prefrontal cortex and other brain regions responsible for emotional regulation or social interactions during deception - Different types of deception=different areas in prefrontal cortex and amygdala activated - A simple lie revealed increased brain activity in the left dorsolateral and right anterior prefrontal cortices supporting the interpretation of previous studies that executive functions are related to making untruthful responses - The main effect of deceiving the interrogator showed activations of ventromedial prefrontal cortex and amygdala - This provides evidence that brain regions assumed to be responsible for Magnetic Resonance Imaging emotional processing or social interaction, are pivotal in telling lies. - High-resolution images are constructed from the measurement of waves that hydrogen atoms emit when they are activated by radio-frequency waves in a magnetic field. Functional magnetic resonance - MRI provides clearer images of the brain than CT and has high spatial imaging fMRI resolution , it can also produce 3D images. Q: I’m confused as to what the difference is between MRI and fMRI. In the text, MRI is detected - This is a technique for determining which parts of the brain are activated by using H atom wave emission but different types of sensation or activity, such as sight, sound or movement of in the notes, it says this for fMRI. subjects fingers. - Images are created from measurements of the waves emitted by hydrogen atoms when they are placed in a magnetic field and its clarity stems from the fact that neural structures diff considerably in their density of H atoms. - When a part of the brain is activated, there is an increase in oxygen because of increased blood flow to the area - These changes in the oxygen content of the blood alter the magnetic properties of the blood’s water (H2O) affecting the MRI signal. So when you have increases and decreases in the MRI signal, you can infer functional changes in the brain. - A BOLD signal (blood-oxygen level dependent) is recorded by oxygenated blood’s magnetic properties. - A series of low resolution scans are taken over time. For some of these scans, the stimulus will be presented and for some the stimulus will be absent and the places of the brain that were activated will be compared. - There are 4 advantages of fMRI over PET: 1. Nothing is injected 2. Provides both structural and functional information in same image 3. Better spatial resolution Awareness in the Vegetative 4. Used to produce 3D images of activity. State Owen et al. - A vegetative state is when patients who emerge from a coma appear to be awake but show no signs of awareness. - Recent functional neuroimaging studies have suggested that islands of preserved brain function may exist in a small percentage of patients who have been diagnosed as vegetative. - fMRI was used on a woman in a vegetative state to measure her neural response during the presentation of spoken sentences which was compared to acoustical noises. - For sentences with ambiguous words, they found an increased activity. - A second fMRI was done where the patient was given spoken instructions to perform 2 mental imagery tasks at specific points during the scan. o Ex. Playing a game of tennis and visiting all the rooms of her house. - The patient still had activity in the supplementary motor area, parahippocampal gyrus, posterior parietal cortex and lateral premotor cortex, just like a healthy person. Magnetoencephalography (MEG) - Imaging technique used to measure the magnetic fields produced
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