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A 12-Channel, real-time near-infrared spectroscopy instrument for brain-computer interface applications

ABSTRACT A continuous wave near-infrared spectroscopy (NIRS) instrument for brain-computer interface (BCI) applications is presented. In the literature, experiments have been carried out on subjects with such motor degenerative diseases as amyotrophic lateral sclerosis, which have demonstrated the suitability of NIRS to access intentional functional activity, which could be used in a BCI as a communication aid. Specifically, a real-time, multiple channel NIRS tool is needed to realise access to even a few different mental states, for reasonable baud rates. The 12-channel instrument described here has a spatial resolution of 30 mm, employing a flexible software demodulation scheme. Temporal resolution of approximately 100 ms is maintained since typical topographic imaging is not needed, since we are only interested in exploiting the vascular response for BCI control. A simple experiment demonstrates the ability of the system to report on haemodynamics during single trial mental arithmetic tasks. Multiple trial averaging is not required.

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Available from: Barak A. Pearlmutter, May 30, 2015
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    ABSTRACT: Transcranial direct current stimulation (tDCS) has been shown to modulate cortical neural activity (Nitsche and Paulus 2000). During neural activity, the electric currents from excitable membranes of brain tissue superimpose at a given location in the extracellular medium and generate a potential, which is referred to as the electroencephalogram (EEG) when recorded from the scalp (Nunez and Srinivasan 2006). Respective neural activity has been shown to be closely related, spatially and temporally, to cerebral blood flow (CBF) that supplies glucose via neurovascular coupling (Girouard and Iadecola 2006). The hemodynamic response to neural activity can be captured by near-infrared spectroscopy (NIRS), which enables continuous monitoring of cerebral oxygenation and blood volume (Siesler et al. 2008). Here, the CBF is increased in the brain regions with neural activity via metabolic coupling mechanisms (Attwell et al. 2010). Cerebral autoregulation mechanisms ensure that the blood flow is maintained during changes in the perfusion pressure (Lucas et al. 2010). We proposed a phenomological model for metabolic coupling mechanisms (Attwell et al. 2010) to capture cerebrovascular reactivity (CVR) that represented the capacity of blood vessels to dilate during anodal tDCS due to neuronal activity-caused increased demands of oxygen (Dutta et al. 2013). Crosssectional studies suggest that impaired cerebral hemodynamics precedes stroke and transient ischaemic attacks (TIA). CVR reflects the capacity of blood vessels to dilate, and is an important marker for brain vascular reserve (Markus and Cullinane 2001). Therefore, cerebrovascular reserve capacity may have a predictive value for the risk of cerebral infarction in patients with reduced cerebrovascular reserve capacity such that it might evolve as a part of routine diagnostic neuroangiologic program (Stoll and Hamann 2002).
    09/2014, Degree: Master of Science in Cerebrovascular Medicine, Supervisor: Michael A. Nitsche
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    ABSTRACT: Objective: A method for electroencephalography (EEG) - near-infrared spectroscopy (NIRS) based assessment of neurovascular coupling (NVC) during anodal transcranial direct current stimulation (tDCS) is presented. Methods: Anodal tDCS modulates cortical neural activity leading to a hemodynamic response, which was used to identify impaired NVC functionality. In this study, the hemodynamic response was estimated with NIRS. NIRS recorded changes in oxy-hemoglobin ( ) and deoxy-hemoglobin ( ) concentrations during anodal tDCS-induced activation of the cortical region located under the electrode and in-between the light sources and detectors. Anodal tDCS-induced alterations in the underlying neuronal current generators were also captured with EEG. Then, a method for the assessment of NVC underlying the site of anodal tDCS was proposed that leverages the Hilbert-Huang Transform. Results: The case series including four chronic (>6 months) ischemic stroke survivors (3 males, 1 female from age 31 to 76) showed non-stationary effects of anodal tDCS on EEG that correlated with the response. Here, the initial dip in at the beginning of anodal tDCS corresponded with an increase in the log-transformed mean-power of EEG within 0.5Hz-11.25Hz frequency band. The cross-correlation coefficient changed signs but was comparable across subjects during and after anodal tDCS. The log-transformed mean-power of EEG lagged response during tDCS but then led post-tDCS. Conclusion: This case series demonstrates changes in the degree of neurovascular coupling to a 0.526A/m2 square-pulse (0-30sec) of anodal tDCS. The initial dip in needs to be carefully investigated in a larger cohort, for example in patients with small vessel disease.
    Journal of Medical Systems 10/2014; · 1.37 Impact Factor
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    ABSTRACT: Objective: A method for electroencephalography (EEG) - near-infrared spectroscopy (NIRS) based assessment of neurovascular coupling (NVC) during anodal transcranial direct current stimulation (tDCS). Methods: Anodal tDCS modulates cortical neural activity leading to a hemodynamic response, which was used to identify impaired NVC functionality. In this study, the hemodynamic response was estimated with NIRS. NIRS recorded changes in oxy-hemoglobin ( ) and deoxy-hemoglobin ( ) concentrations during anodal tDCS-induced activation of the cortical region located under the electrode and in-between the light sources and detectors. Anodal tDCS-induced alterations in the underlying neuronal current generators were also captured with EEG. Then, a method for the assessment of NVC underlying the site of anodal tDCS was proposed that leverages the Hilbert-Huang Transform. Results: The case series including four chronic (>6 months) ischemic stroke survivors (3 males, 1 female from age 31 to 76) showed non-stationary effects of anodal tDCS on EEG that correlated with the response. Here, the initial dip in at the beginning of anodal tDCS corresponded with an increase in the log-transformed mean-power of EEG within 0.5Hz-11.25Hz frequency band. The cross-correlation coefficient changed signs but was comparable across subjects during and after anodal tDCS. The log-transformed mean-power of EEG lagged response during tDCS but then led post-tDCS. Conclusion: This case series demonstrated changes in the degree of neurovascular coupling to a 0.526A/m2 square-pulse (0-30sec) of anodal tDCS. The initial dip in needs to be carefully investigated in a larger cohort, for example in patients with small vessel disease. Keywords: neurovascular coupling, electroencephalography, near-infrared spectroscopy, Hilbert-Huang Transform.
    Journal of Medical Systems 10/2014; DOI:10.1007/s10916-015-0205-7 · 1.37 Impact Factor