Multi-echo investigations of positive and negative CBF and concomitant BOLD changes

Area of Science:

• Neuroimaging
• Physiology
• Brain Function

Background:

• The origin of negative BOLD signal changes (NBR), or 'deactivation', is debated.
• Positive BOLD responses (PBR) typically indicate brain activation.

Purpose of the Study:

• To investigate the physiological mechanisms underlying NBR.
• To compare cerebral blood flow (CBF) and BOLD changes in deactivated versus activated brain regions.

Main Methods:

• Utilized a novel multi-echo EPI sequence with pseudo-continuous arterial spin labeling (pCASL) for simultaneous CBF and BOLD detection at 3T.
• Measured absolute and relative changes in CBF, R2*, and coupling ratios in the human visual cortex.
• Analyzed the temporal characteristics of functional responses.

Main Results:

• Observed differences in CBF and R2* between activated and deactivated regions.
• Identified distinct flow-metabolism coupling ratios in NBR compared to PBR.
• Noted faster NBR with more pronounced post-stimulus transients.

Conclusions:

• Findings suggest distinct physiological underpinnings for negative BOLD responses.
• Differences in flow-metabolism coupling may reflect variations in neuronal activity.
• Advanced imaging techniques improve sensitivity for simultaneous CBF and BOLD measurements.