Ling 390 6

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LING 390
Andrea Nicole Santi Isabelle Deschamps

Sept 21 - Anatomical MRI vs fMRI - regular mris just give you structure. functional looks for modules. you need anatomy for functional too. - fMRI: what is it? - in order to answer this question, we will look at: - the equipment - giant magnet coil thing - the basis of the signal - it's too difficult to understand how the signal is generated for this class - fMri - Magnetization: magnetic fields and spins (protons in the body become aligned to the field) - fmRi -Excitation: radio frequency pulses knock protons over - Relaxation times: then they go back to their state of alignment with the field, they emit energy that the coil receives - fmrI - Tissue Contrasts: make it possible to encode the spatial information of signal - Fmri - Bold and T2* : concentration of hydrogen in an area (anatomical MRI); amount of oxy- vs. deoxyhemoglobin in an area (functional MRI) - normally, our protons all spin at their own orientation. when you put them in the magnetic field, they all align with it. once they're all ligned up, we disturb them with a radio frequency pulse, causing the protons to go from low to high energy states. depending on the frequency applied, you can disturb different protons and change them differently - T1 is the time is takes the protons to realign with the magnetic field - T2 is the time it takes for the protons to get back to spinning in unison - T2* measures the overall decay of the observable RF signal over a macroscopic region (fMRI signal) - every tissue has its own T1 and T2 value: this is how we differentiate between things - T1- weighted MRi have good grey/white matter contrast - T2-weighted MRI are sensitive to water content - usually, we use T1-weighed in psychology, because the water content isn't as useful - The variations in BOLD signals come from three things: a) increase in neural activity (which causes an increase in oxygen and glucose)
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