RESEARCH ARTICLE


Spatially Extended fMRI Signal Response to Stimulus in Non-Functionally Relevant Regions of the Human Brain: Preliminary Results



John Kornak*, 1, Deborah A Hall2, Mark P Haggard3
1 Department of Epidemiology and Biostatistics, University of California, San Francisco, USA
2 Division of Psychology, Nottingham Trent University, United Kingdom
3 Department of Experimental Psychology, University of Cambridge, United Kingdom


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© Kornak et al; Licensee Bentham Open

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Department of Epidemiology and Biostatistics, University of California, San Francisco, 185 Berry Street, Lobby 5, Ste 5700, San Francisco, CA 94107-1762, USA; Tel: ++1 - 415 - 514 8028; Fax: ++1 - 415 - 514 8150; E-mail: john.kornak@ucsf.edu


Abstract

The blood-oxygenation level dependent (BOLD) haemodynamic response function (HDR) in functional magnetic resonance imaging (fMRI) is a delayed and indirect marker of brain activity. In this single case study a small BOLD response synchronised with the stimulus paradigm is found globally, i.e. in all areas outside those of expected activation in a single subject study. The nature of the global response has similar shape properties to the archetypal BOLD HDR, with an early positive signal and a late negative response typical of the negative overshoot. Fitting Poisson curves to these responses showed that voxels were potentially split into two sets: one with dominantly positive signal and the other predominantly negative. A description, quantification and mapping of the global BOLD response is provided along with a 2 × 2 classification table test to demonstrate existence with very high statistical confidence. Potential explanations of the global response are proposed in terms of 1) global HDR balancing; 2) resting state network modulation; and 3) biological systems synchronised with the stimulus cycle. Whilst these widespread and low-level patterns seem unlikely to provide additional information for determining activation in functional neuroimaging studies as conceived in the last 15 years, knowledge of their properties may assist more comprehensive accounts of brain connectivity in the future.

Keywords: Blood oxygenation level dependency, functional MRI, global haemodynamic effect, haemodynamic parameters, haemodynamic response function, least squares estimation, negative-responding voxels, parameter estimation, Poisson curve, variable haemodynamic delay.