Functional study of the brain and peripheral nerves using near-infrared spectroscopy

We conducted functional study of the brain and peripheral nerves using near-infrared spectroscopy (NIRS). Tissues are relatively transparent in the light of near infrared range (600-∼1000nm). Light in this wavelength range can penetrate several centimeters and be able to probe the areas where the neuronal activities happen.;There have been many reports on functional brain studies using NIRS. However, we found there are still common mistakes in the NIRS data analysis. One of them is to apply the standard t test for multiple comparisons of correlated data. In this work, we present a study showing that misleading results may be obtained using this approach. We also studied the occurrence of errors of type I, i.e. the occurrence of falsely significant points, and the effects of digital filtering procedures. We showed the improved performance of a modified t test, the Dubey/Armitage-Parmar algorithm.;In functional brain study, we are one of the few groups combining NIRS and magnetic resonance imaging (MRI). We present a new method for calculating the functional MRI BOLD signal (blood oxygen level dependent) which is appropriate for comparison with the changes in hemoglobin measured with NIRS during brain activation. We present a case study where we found that the new BOLD signal has similar spatial and temporal features to the changes of oxy- and deoxy-hemoglobin concentrations measured by NIRS, which reinforced the idea that both fMRI and NIRS are sensitive to similar underlying hemodynamic changes.;As brain has always been the focus of functional NIRS, we initiated a study on the peripheral nervous system (PNS). In this work, we present a study of the near-infrared optical response to electrical stimulation of the sural nerve. We measured optical changes that peaked 60-160 ms after the electrical stimulus. On the basis of the strong wavelength dependence of these fast optical signals, we argue that the origin is from absorption rather than scattering. We have also investigated the skin motion associated with electrical stimulus and its potential effects on the optical signal.