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Techniques fmri pet optical imaging 64 functional

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Unformatted text preview: of the brain as a participant does different tasks Three major techniques: fMRI, PET, Optical Imaging 64 Functional Magnetic Resonance Imaging (fMRI) Fundamental basis is that resonating atomic nuclei in a magnetic field emit signals at a characteristic frequency that can be measured to produce a 3-dimensional image. The emitted signals vary as a function of blood oxygenation levels because of changes in the magnetic properties of hemoglobin when oxygen binds to it or separates from it. These signal changes can be used to simultaneously image changes in the flow of oxygenated blood to different areas of the brain, which are related to the relative amounts of neural activity changes in these areas. 65 66 fMRI Scanner and Data A human MRI scanner (above) and data (right) showing the location of activations in motor cortex during movement (yellow), activations from an auditory verb generation task (red), and from a visual verb generation task (blue) in a single subject. “Activations” are usually the result of subtracting the amount of signal between two different behavioral conditions. 67 Positron Emission Tomography (PET) Participant is injected with short-lived radioactive probe, which can be a positron-emitting form of oxygen (to study blood flow), a chemicallymodified sugar (to study brain cell activity), or a drug that binds to a particular neurotransmitter receptor (to study changes in signaling of a particular neurotransmitter system) . Changes in the concentration of the probe in activated brain areas are measurable and can be used to generate a 3-dimensional image. PET Scanner and Data Radioactive tag on probe molecule decays to produce simultaneous gamma rays at 180° angles Human PET scanner Sections through 3-D human datasets (labeled oxygen for blood flow) 3-D dataset from Simultaneous gamma rays detected by a chicken embryo ring of crystal detectors- this is the basis (labeled sugar shows cell activation) for computer reconstructions in 3-D 68 Optical Imaging INVASIVE – usually used in experimental animals only Employs a sensitive video camera to measure changes in light absorption or reflection that occur in neurons when they are active – only measures these events when they occur near the surface of the brain (can also use on people undergoing neurosurgery) 605-700 nm Need to average data over a large number of trials to remove noise Based on activity-related changes in light reflectance due in part to changes in blood oxygen content; active regions absorb more red light. 69...
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