Origins of the BOLD post-stimulus undershoot

Area of Science:

• Neuroimaging and neuroscience
• Brain function and metabolism

Background:

• The blood-oxygenation level-dependent (BOLD) signal's post-stimulus undershoot is crucial for understanding brain energy and neurovascular coupling.
• Existing theories propose venous ballooning or prolonged elevated oxygen consumption as causes for the BOLD undershoot.
• The role of cerebral blood flow (CBF) changes in the BOLD undershoot is also under investigation.

Purpose of the Study:

• To elucidate the contribution of the venous compartment to the BOLD signal's post-stimulus undershoot.
• To differentiate between venous ballooning and other factors influencing the BOLD undershoot.

Main Methods:

• In vivo functional magnetic resonance imaging (fMRI) was used to measure transient changes in venous blood volume (CBV(v)), CBF, and BOLD responses in healthy humans.
• Simultaneous measurement of DeltaCBV(v), DeltaCBF, and DeltaBOLD allowed for detailed analysis of the BOLD signal dynamics.

Main Results:

• A slow post-stimulus recovery of venous CBV was observed, supporting the passive venous "balloon" effect.
• Findings suggest that previous estimates of total CBV recovery might be influenced by arterial CBV dynamics.
• Significant contribution of CBF undershoots to the BOLD undershoot was identified.

Conclusions:

• The study supports a passive venous ballooning mechanism contributing to the BOLD undershoot.
• CBF undershoots, in conjunction with slow venous CBV response, significantly explain the observed BOLD undershoot.
• These findings refine our understanding of the neurovascular response and brain energy metabolism during BOLD signal transients.