False positives in functional near-infrared 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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    • "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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    • "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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    • "Therefore, in the first instance only comparisons of our study with those involving frontal anagram-evoked stimulation and activation in healthy adults would seem judicious [24,27,28,42–44]. Furthermore, because participants in the present study were subjected to an unusually prolonged task, only studies with similar task duration are considered in the comparison [24,27,28]. In this context, the time to-peak-response found in the present study is of the same order of magnitude as reported in other studies (~1 min), albeit longer. "
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