Evidence of faster hemodynamic response function at weak sensory stimulus levels supports higher frequency intrinsic functional connectivity

There has been emerging evidence that resting state spontaneous neural fluctuations can persist at frequencies not supported by the canonical hemodynamic response function (HRF). As RS may likely comprise varying levels of spontaneous stimuli, it is thus of interest to query whether BOLD fluctuations elicited by small-intensity stimuli occur at faster time scales than the canonical HRF and can account for certain high-frequency (HF) phenomena observed at rest. Here, we employ a vibrotactile stimulus with graded contrasts, and show that HRFs elicited by small intensity stimuli have faster time-to-peak and narrower dispersions than canonical HRFs, thus may promise elevated BOLD responses in higher frequency bands and explain part of the HF phenomena observed in recent RS studies.