The cerebrum is responsible for mental activity.

Neither fMRI machines nor people interpreting data from fMRI machines can tell if an individual is lying. fMRI machines can show regions that are activated by certain tasks; however, fMRI machines do not provide causation, only correlation (e.g. task Y doesn't necessarily require brain region X). Since a single brain region can be involved in multiple tasks, it would be nearly impossible to say with any certainty "X region is the region for lying" and to conclude that activation in this region suggests that an individual is lying.

Federal Monetary Residence Improvement

fMRI measures the amount of oxygenated blood over time. Deoxygenated and oxygenated blood have different magnetic properties which an fMRI scanner can detect.

In scientific terms, the acronym "FMRI" stands for "Functional Magnetic Resonance Imaging". It is used to scan a patient's body (specifically the brain) by using magnetic waves.