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 single-subject 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 = 0.9745 ± 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. Copyright © 2011 Wiley Periodicals, Inc.