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
Local neural activity also leads to a
corresponding response in cerebral blood ﬂow
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 &
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
- Magnetic resonance imaging, Functional magnetic resonance, neural activity, BOLD Signal, Functional magnetic resonance imaging