Electroencephalography (EEG)-near-infrared spectroscopy (NIRS) based online imaging during non-invasive electrical brain stimulation
Résumé
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).
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