False Positives In Functional Nearinfrared Topography

Department of Medical Physics and Bioengineering, Malet Place Engineering Building, University College London, Gower Street, London WC1E 6BT, UK.
Advances in Experimental Medicine and Biology (Impact Factor: 1.96). 02/2009; 645:307-14. DOI: 10.1007/978-0-387-85998-9_46
Source: PubMed


Functional cranial near-infrared spectroscopy (NIRS) has been widely used to investigate the haemodynamic changes which occur in response to functional activation. The technique exploits the different absorption spectra of oxy- and deoxy-haemoglobin ([HbO2] [HHb]) in the near-infrared region to measure the changes in oxygenation and haemodynamics in the cortical tissue. The aim of this study was to use an optical topography system to produce topographic maps of the haemodynamic response of both frontal cortex (FC) and motor cortex (MC) during anagram solving while simultaneously monitoring the systemic physiology (mean blood pressure, heart rate, scalp flux). A total of 22 young healthy adults were studied. The activation paradigm comprised of 4-, 6- and 8- letter anagrams. 12 channels of the optical topography system were positioned over the FC and 12 channels over the MC. During the task 12 subjects demonstrated a significant change in at least one systemic variable (p < or = 0.05). Statistical analysis of task-related changes in [HbO2] and [HHb], based on a Student's t-test was insufficient to distinguish between cortical haemodynamic activation and systemic interference. This lead to false positive haemodynamic maps of activation. It is therefore necessary to use statistical testing that incorporates the systemic changes that occur during brain activation.

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Available from: Caroline B Reid
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    • "Confounding effects on the observed signal were then estimated and removed during model inversion. Note that additional measurements of systemic confounds e.g., changes in blood pressure (Minati et al., 2011; Tachtsidis et al., 2009; Takahashi et al., 2011) and arterial partial pressure of CO 2 (Scholkmann et al., 2013) can also be used in the proposed method, which may enhance the efficiency of effective connectivity estimates. "
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    ABSTRACT: Functional near-infrared spectroscopy (fNIRS) is an emerging technique for measuring changes in cerebral hemoglobin concentration via optical absorption changes. Although there is great interest in using fNIRS to study brain connectivity, current methods are unable to infer the directionality of neuronal connections. In this paper, we apply Dynamic Causal Modelling (DCM) to fNIRS data. Specifically, we present a generative model of how observed fNIRS data are caused by interactions among hidden neuronal states. Inversion of this generative model, using an established Bayesian framework (variational Laplace), then enables inference about changes in directed connectivity at the neuronal level. Using experimental data acquired during motor imagery and motor execution tasks, we show that directed (i.e., effective) connectivity from supplementary motor area to primary motor cortex is negatively modulated by motor imagery, and this suppressive influence causes reduced activity in primary motor cortex during motor imagery. These results are consistent with findings of previous functional magnetic resonance imaging (fMRI) studies, suggesting that the proposed method enables one to infer directed interactions in the brain mediated by neuronal dynamics from measurements of optical density changes. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
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    • "Studies have shown transient changes in blood pressure (e.g. [8] [9] [10]) and partial pressure of CO 2 (measured as end-tidal CO 2 ) (e.g. [11] [12] [13]) cause local changes in brain hemodynamics and oxygenation which interfere with the measurement of the local neuro-vascular coupling. "
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    • "e l s e v i e r . c o m / l o c a t e / y n i m g that some individual variability in correlation between fNIRS signal and scalp blood flow or mean blood pressure (Tachtsidis et al., 2008a) and that the systemic changes that also affect extracranial signals can lead to false positives in fNIRS signals (Tachtsidis et al., 2009). It has also been reported that regional cerebral oxygen saturation is affected by extracranial contamination (Davie and Grocott, 2012; Sørensen et al., 2012). "
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