Psy 123_Lec 5

So one of the questions is what are we measuring

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Unformatted text preview: eural activity (which is what we are actually trying to measuring). So one of the questions is, what are we measuring?? Clearly it is not just a single neuron... Fick Principle! (flow increases >> metabolic rate increases ! Decreased ratio: deoxy-HB / oxy-HB! Less spin dephasing from magnetic inhomogeneities caused by deoxy-HB! Increased MR signal! DeYoe et al., 1994! Physiological issues of the BOLD signal! Local neural activity leads very rapidly (.5 to 2.5 seconds) to oxygen consumption (OC) in the immediate area.! Local neural activity also leads to a corresponding response in cerebral blood flow (CBF).! CBF exceeds the corresponding increase in OC.! CBF is broader and slower (peaks 5 - 6 seconds after the onset of the neural activity) than OC.! If you just look at BOLD signal across time then you see it dips below baseline, then rises and peaks for 5-6 sec. We can track this very carefully, and if enough studies than we can actually get this signature. BOLD! +! BOLD = deoxyHb/oxyHb! seconds! Physiological issues of the BOLD signal! BOLD is directly related to localized cerebral blood flow & oxygen consumption.! BOLD can be sampled from small “voxels” within the brain (e.g., 3mm x 3mm x 5mm; 60,000 voxels across the whole brain).! BOLD is monotonic and additi...
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  • Fall '11
  • Staff
  • Magnetic resonance imaging, Functional magnetic resonance, neural activity, BOLD Signal, Functional magnetic resonance imaging

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