The previous chapter discussed the application of near-infrared spectroscopy (NIRS) and near-infrared imaging (NIRI) to brain activity monitoring and compared them to other functional neuroimaging modalities. This chapter continues the theme by exploring the simultaneous use of functional nearinfrared spectroscopy (fNIRS) and such functional neuroimaging modalities as electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI). It also presents a review of some current studies and novel approaches, particularly those used to enhance penetration depth in NIRS imaging.
Multimodal measurements are increasingly being employed in the study of human physiology. Brain studies in particular can take advantage of the exciting possibility of combining data from different techniques, based on causality in brain activity - an increase in neuronal activity causes a metabolic demand for glucose and oxygen, which increases cerebral blood flow (CBF) to the active brain region. Studying the mechanisms and relationships between among activities, electrophysiology, and blood-flow-related parameters requires combining hemodynamic and electromagnetic-based imaging techniques. By simultaneously monitoring such physiological parameters as heart rate, blood pressure and blood flow, changes in respiration and end-tidal carbon dioxide levels, and shifts in blood flow distribution in the human body, we are able to study the functioning of organs, gaining a more comprehensive understanding of the interconnections between different physiological activities and their relation to brain function. Moreover, multimodal measurements of this type provide tools for identifying physiological components generated by the brain.
Performing multimodal measurements by combining EEG with MEG or fMRI is a common practice in modern-day neuroimaging. Since these three imaging modalities are increasingly being used with functional fNIRS, the following presentation provides a brief introduction to EEG, MEG, and fMRI; discusses their utilization in combination with fNIRS; and explores additional benefits offered by the simultaneous use of fNIRS and these imaging modalities. Furthermore, examples of recent multimodal studies involving the application fNIRS are presented.
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