Quantifying hemodynamic refractory bold effects in normal subjects at the single‐subject level using an inverse logit fitting procedure

Abstract

Purpose: To evaluate whether hemodynamic refractory effects provoked by repeated visual stimulation can be detected and quantified at the single-subject level using a recently described hemodynamic response function (HRF) fitting algorithm. Materials and Methods:Hemodynamic refractory effects were induced with an easily applicable functional MRI (fMRI) paradigm. A fitting method with inverse logit (IL) functions was applied to quantify net HRFs at the singlesubject level with three interstimulus intervals (ISI; 1, 2, and 6 s). The model yielded amplitude, latencies, and width for each HRF.Results: HRF fitting was possible in 44 of 51 healthy volunteers, with excellent goodness-of-fit (R 2 ¼ 0.9745 6 0.0241). Refractory effects were most pronounced for the 1-s ISI (P < 0.001) and had nearly disappeared for the 6-s ISI.Conclusion: Quantifying refractory effects in individuals was possible in 86.3% of normal subjects using the IL fitting algorithm. This setup may be suitable to explore such effects in individual patients.

fMRI hemodynamics accurately reflects neuronal timing in the human brain measured by MEG

“…Among the three timing indices, TTH showed the smallest variance (Table 1). Therefore, analogous to several previous studies (Descamps et al, 2012; Liu et al, 2005; Waugh et al, 2008; Weilke et al, 2001) and consistent with our prediction that TTH may offer more robust estimates than Onset and TTP , TTH was considered the most reliable measure of HDR latency (results for Onset and TTP are, however, reported as well; see Tables 1 and 2). …”

Statistical modeling of time‐dependent fMRI activation effects

“…181]. In some cases, the basis functions contain additional unknown parameters, such as the inverse logit model, which consists of the superposition of three inverse logit functions [Descamps et al, 2012;Lindquist and Wager, 2007].…”