Modelling confounding effects from extracerebral contamination and systemic factors on functional near-infrared spectroscopy

Matthew Caldwell,Felix Scholkmann,Ursula Wolf,Martin Wolf,Clare Elwell,Ilias Tachtsidis

doi:10.1016/j.neuroimage.2016.08.058

Matthew Caldwell, Felix Scholkmann + Show 4 more

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https://doi.org/10.1016/j.neuroimage.2016.08.058

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Abstract

Haemodynamics-based neuroimaging is widely used to study brain function. Regional blood flow changes characteristic of neurovascular coupling provide an important marker of neuronal activation. However, changes in systemic physiological parameters such as blood pressure and concentration of CO2 can also affect regional blood flow and may confound haemodynamics-based neuroimaging. Measurements with functional near-infrared spectroscopy (fNIRS) may additionally be confounded by blood flow and oxygenation changes in extracerebral tissue layers. Here we investigate these confounds using an extended version of an existing computational model of cerebral physiology, ‘BrainSignals’. Our results show that confounding from systemic physiological factors is able to produce misleading haemodynamic responses in both positive and negative directions. By applying the model to data from previous fNIRS studies, we demonstrate that such potentially deceptive responses can indeed occur in at least some experimental scenarios. It is therefore important to record the major potential confounders in the course of fNIRS experiments. Our model may then allow the observed behaviour to be attributed among the potential causes and hence reduce identification errors.

Highlights

Neuroimaging techniques relying on changes in tissue haemodynamics and oxygenation, such as functional near-infrared spectroscopy and blood oxygen level dependent (BOLD) based functional magnetic resonance imaging, have been widely and productively used to investigate cerebral function
We have used a modified version of the BrainSignals physiological model, termed BSX, to investigate the susceptibility of functional neuroimaging to confounding by systemic factors and extracerebral tissues
While extracerebral influences are relevant to functional near-infrared spectroscopy (fNIRS), systemic confounding is of utmost concern for other haemodynamics-based modalities such as BOLD-f MRI

Summary

Introduction

Neuroimaging techniques relying on changes in tissue haemodynamics and oxygenation, such as functional near-infrared spectroscopy (fNIRS) and blood oxygen level dependent (BOLD) based functional magnetic resonance imaging (fMRI), have been widely and productively used to investigate cerebral function. In the case of fNIRS, there is further scope for confounds arising from haemodynamic/oxygenation changes in the extracerebral compartment of the head. Near-infrared light passes through the overlying scalp and skull tissue layers in order to interrogate the cerebral tissues underneath, and significant optical absorption and scattering can occur in these layers (Franceschini et al, 1998; Kirilina et al, 2012; Erdoğan et al, 2014). It is important to understand and account for such potential confounds in order to reach reliable conclusions (Minati et al, 2011; Scholkmann et al, 2014b; Tachtsidis and Scholkmann, 2016). Numerous approaches have been proposed, ranging from purely statistical signal processing to biophysical modelling at various levels of detail

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