I could listen to this professor all day, the way she explains topics is just so amazing and concise. As a visual learner, I find her diagrams make the topic so much easier to understand. Thank you!
So basically there are two beta values that are mentioned in the video. First beta is the amplitude of HRF that is assumed to be constant and second is the coefficient of the general linear model that explains the variance in measured signal explained by the HRF. Am i right?The way she explains can be confusing to students. I think even the teacher is not truly sure what it is!!
unless the "predicted" value on the x axis in that linear model means a "standard" version, assuming the HRF amplitutde being 1, so the correlation coefficient really equals the beta as the HRF amplitutude. Not sure if I understand it correctly!
Sorry if this is a dumb question, but is the HrF curve a consequence of oxygen levels delivered to individual neurons by astrocytes? Or is it the sum total of oxygen levels within a voxel? If so, would the HrF curve change if spatial resolution was increased?
Did I get it wrong? Or was it true? Is there really a one-to-one correspondence between blood vessels and neurons? Where she is explaining the astrocytes. She says that each astrocyte controls a blood flow that is feeding the neuron. This means per each neuron we have one blood vessel. Of course, I am wrong and confused :)
Hey Shah, :) Various mechanisms, both neuronal and glial, will contribute to the regulation of blood flow. Astrocytes contribute to the principle of cerebral blood flow (in several ways): (1) Calcium-dependent synthesis of metabolites of arachidonic acid by astrocytes modulates cerebral blood flow. (2) Synthesis of PGE2 and EETs dilate blood vessels. (3) Synthesis of 20-HETE constricts vessels. (4) The release of K+ may also contribute to vasodilation. (5) The generation of vascular tone: astrocytes release 20-HETE and ATP that constrict vascular smooth muscle cells, which leads to generating of vessel tone. "However, the precise role that astrocytes play in regulating blood flow remains an open question, as the neurotransmitters that evoke astrocytic Ca2+ signaling and the time course of the astrocytic Ca2+ signals remain in dispute" - MacVicar et al. l. The metabolic state of the brain (for example, pO2 levels) influences astrocytic control of cerebral blood flow: e.g., the pO2 level determines the domination of vasodilation or constriction.
Great lectures! One doubt - the beta value is calculated as the amplitude for the best fit of our model to the BOLD data. But won't the 'fitness' of the fit or the correlation of fit change for every voxel? Wouldn't the 'bestness' of best-fit change then for every voxel?
Basically there are two beta values that are mentioned in the video. First beta is the amplitude of HRF that is assumed to be constant and second is the coefficient of the general linear model that explains the variance in measured signal explained by the HRF.
