Temporal Characteristics of Functional MRI Signal

Abstract

Functional MRI (fMRI) utilizing blood oxygenation level-dependent (BOLD) contrast has been extensively developed to study different functional aspects of the human brain. During functional brain activity, the cerebral metabolic rate of oxygen consumption (CMRO2) was found to be much less than that of cerebral blood flow (CBF), which lead to an increase of the BOLD signal. However, because the BOLD signal is due to complicated inter-play between CBF, CMRO2, and cerebral blood volume (CBV), the physiological mechanism behind the BOLD signal is not well understood. Recently, many finer temporal characteristics of the BOLD signal have been demonstrated, which include an initial dip, an overshoot, a pleatau and an undershoot before returning to the baseline. In addition, linearity of functional BOLD signal behavior has been investigated based on both physiological interests and the advances of the task design. Such findings can improve our knoweledge of the hemodynamic response due to neuronal activity, and the use of fMRI techniques applied in the understanding of different processes of the brain.