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


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
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    • "For example, the NIR light sources can be amplitude-modulated at different carrier frequencies with a gap (viz. 2 to 4 KHz in steps of 200Hz) using a driving circuit that includes a multiplexer and driver for the laser diode (LD) or light emitting diode (LED) to emit NIR light in consecutive time slots. LED, which emit incoherent and uncollimated light, is preferred since it allows the emission of more NIR photons into the tissue than LD with the same maximum permissible exposure (Soraghan et al. 2008). Dual-wavelength LEDs can be used instead of two separate LEDs (as in our 4-channel low-cost CW NIRS system, Figure 2.2a) in a multi-channel high density whole head system. "
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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).
    Full-text · Thesis · Sep 2014
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    • "Although the price is much lower than fMRI, commercial product is still very expensive. For the need of neuroimaging research by f NIRS, many laboratories have tried to build custom-made systems with more flexibility and lower cost [12] [13] [14] [15] [16] [17] [18]. For CW-f NIRS instrumentation, we can choose either embedded system or system based on data acquisition (DAQ) device as a candidate for hardware platform. "
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    ABSTRACT: In the last two decades, functional near-infrared spectroscopy (fNIRS) is getting more and more popular as a neuroimaging technique. The fNIRS instrument can be used to measure local hemodynamic response, which indirectly reflects the functional neural activities in human brain. In this study, an easily implemented way to establish DAQ-device-based fNIRS system was proposed. Basic instrumentation components (light sources driving, signal conditioning, sensors, and optical fiber) of the fNIRS system were described. The digital in-phase and quadrature demodulation method was applied in LabVIEW software to distinguish light sources from different emitters. The effectiveness of the custom-made system was verified by simultaneous measurement with a commercial instrument ETG-4000 during Valsalva maneuver experiment. The light intensity data acquired from two systems were highly correlated for lower wavelength (Pearson's correlation coefficient r = 0.92, P < 0.01) and higher wavelength (r = 0.84, P < 0.01). Further, another mental arithmetic experiment was implemented to detect neural activation in the prefrontal cortex. For 9 participants, significant cerebral activation was detected in 6 subjects (P < 0.05) for oxyhemoglobin and in 8 subjects (P < 0.01) for deoxyhemoglobin.
    Full-text · Article · Aug 2014 · Computational and Mathematical Methods in Medicine
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    • "Though this response appears several seconds after the activation, the property of high spatial resolution makes fNIRS an advantage to set up a BCI system. Currently, few researches have been done to build an fNIRS-based BCI system [7] [8] [9]. Most motor imaginary paradigms used for both EEG and fNIRS based BCI systems are movement of different limbs, such as left hand, right hand, foot, tongue, or other hand movements. "
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    ABSTRACT: In this paper, we present a Brain Computer Interface (BCI) system using multichannel functional near-infrared spectroscopy (fNIRS) signal acquired when subjects execute speed and force imagination of right hand. Our goal is to classify much more movement imagination details so that a BCI system can provide more control commands, which is helpful for BCI application. Six subjects (3 male, 3 female) participate in the experiment for 3 sessions. We use Gaussian filter and wavelet-MDL to preprocess the acquired signal, and then use support vector machine (SVM) to classify task state versus rest state and speed imagination versus force imagination. Our results show that using oxyhemoglobin (HbO) data as feature can get comparable results with condition of using both HbO and hemoglobin (Hb) data as feature. Also, feature from left head provide more information than right head when subjects doing right hand movement imagination. Finally we study feature period effects on classification accuracy and find some key periods dominating the results. Our study demonstrates that an fNIRS based BCI have the potential to provide more control commands for a real application
    Full-text · Conference Paper · Jan 2011
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