UC Irvine

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.