Question

4. News headlines sometimes claim that a recent fMRI study has shown that cells in a particular part of the brain fire more action potentials during a particular task.

A. What is fMRI is actually detecting?
B. How can one distinguish actual signals from spurious signals?

C. Discuss the idea that the cells in a brain area with a high fMRI signal are firing more action potentials.

Answer 1

A​​​ .fMRI is the functional magnetic resonance imaging or functional MRI measures of brain activity by detecting changes associated with blood flow.This technique relies on the fact that cerebral flow and neuronal activation are coupled.when an area of brain is in use, blood flow to that region also increases.

B. Spurious signals are unintended signals that can result from harmonics,intermodulation , frequency conversion,or EMI( electromagnetic interference). It is caused by unwanted transmitter effects such as harmonics emission, parasitic emission,etc.. The actual fMRI signals hence needs both a strong magnetic field and a pulse sequence such as EPI.The physiological blood flow response largely decides the temporal sensitivity,that is how accurately we can measure when neurons are active,in bold afMRI.

C. Increases in CBF or BOLD responses recorded by functional neuroimaging have traditionally been perceived as representing increases in spike activity in the principal target cells of the active brain region.spike activity is callled the firing of more action. Activation of the cerebral cortex leads to desynchronization of EEG that is not necessarily accompanied by increase in the overall discharge rate of cortical neurons.