Abstract #3727

The dependence of the BOLD response transients on stimulus type and echo time

Martin Havlicek¹, Dimo Ivanov¹, Benedikt A Poser¹, and Kamil Uludag¹

¹Cognitive Neuroscience, Maastricht University, Maastricht, Netherlands

Adaptation and post-stimulus undershoot observed in the BOLD signal can originate from both active neuronal and passive vascular mechanisms. Using a multi-echo GE-EPI functional MRI sequence with two distinct visual stimuli, we are able to show that not only the BOLD response magnitude but also its shape is affected by the echo-time (TE). As pure oxygenation changes predict approximately a linear scaling of the BOLD signal with TE, this finding indicates that the composition of the underlying physiological mechanisms contributing to the fMRI signal (i.e. CBF, CBV, and CMRO₂) varies over time.

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