Abstract #2781

Liau J, Behzadi Y, Liu T

The initial dip in the BOLD signal reflects early transient increases in deoxyhemoglobin and appears to be a more specific marker of neural activity than the later positive BOLD signal. However, the initial dip is not consistently observed in human fMRI studies, possibly due to confounding factors, such as medication and drug usage. In this study we show that caffeine (200 mg dose) can reduce or eliminate the initial dip in the visual BOLD signal. Caffeine usage may therefore be a major source of variability in the detection of the initial dip in human fMRI studies.