Abstract

Using photon-density-wave fluctuation-correlation-spectroscopy, we studied the fluctuations of the optical signal measured in the brain and skeletal muscles. We investigated the autocorrelation power spectra at specific tissue locations, and the coherence between different tissue regions in the frequency band 0-0.3 Hz. We found specific dominant frequency components that can be assigned to vasoconstriction activity. In a measurement protocol involving voluntary motor stimulation (right hand finger movements), we found that the optical fluctuations observed in the left forearm muscle and in the left cerebral motor cortex show different coherence features at rest and during stimulation. These changes are particularly significant at the frequencies associated with vasoconstriction activity. A power-spectrum analysis of the optical fluctuations revealed a resonance-like dependence of the optical signal at the motor cortex on the period of the motor stimulation sequence.

Highlights

  • Photon-density-wave near-infrared (NIR) spectroscopy is a useful method for the non-invasive study of hemodynamic changes in tissue optical properties over time scales ranging from milliseconds to hundreds of seconds

  • We present a NIR study of motor cortex responses to periodic stimulations by means of fluctuation correlation spectroscopy

  • We use this method to assess the dynamics of the optical signal at the motor cortex, and to analyze its coherence with the signals collected at other tissues such as the forearm muscle and the superficial scalp-scull layers

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Summary

INTRODUCTION

Photon-density-wave near-infrared (NIR) spectroscopy is a useful method for the non-invasive study of hemodynamic changes in tissue optical properties over time scales ranging from milliseconds to hundreds of seconds. The most popular method is the folding average of the signals over a number of cycles of repetitive stimulations This approach is effective only in the case of a significant phase synchronization of the optical signal with the stimulation sequence. We present a NIR study of motor cortex responses to periodic stimulations by means of fluctuation correlation spectroscopy We use this method to assess the dynamics of the optical signal at the motor cortex, and to analyze its coherence with the signals collected at other tissues such as the forearm muscle and the superficial scalp-scull layers

INSTRUMENTATION AND METHOD
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RESULTS
DISCUSSION AND CONCLUSION
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