Question

1.

-What physical phenomenon is MRI based on?

-What is the magnetic field gradient? Do we need this in MRI's?

-What is the effect of head motion on an fMRI signal?

-Why would BOLD fMRI signal increase after neuronal activation?

-What is the effect of neuronol activity in the fMRI voxel on its T2*?

Answer 1

•MRI technique is based on the physical phenomenon Nuclear Magnetic Resonance (NMR).

• Magnetic field gradient is the variation in the magnetic field with respect to position. This is important in MRIs to improve the image quality.

•Head motion significantly affects measures of functional connectivity MRI even within the range of motion exhibited by typical, healthy young adults. The effects are dependent on the specific measure and include decreased functional coupling for distributed networks and increased functional coupling for local networks. Since motion was found to be a stable property within subjects behaving as a trait studies of genetic associations, heritability, and relations to behavior and personality will all need to consider the influence of head motion. Analyses that contrast groups that differ in their tendency to move will be particularly vulnerable to the confounding effects of motion, especially when the group more likely to move shows reductions in distributed and increases in local functional coupling (e.g., children and older adults).

•A widely accepted model, established for sensory neo-cortex, suggests that the BOLD signal reflects peri-synaptic activity in the form of the local field potential rather than the spiking rate of individual neurons.