Increase in Low-Frequency Oscillations in fNIRS as Cerebral Response to Auditory Stimulation with Familiar Music

Abstract

Recognition of typical patterns of brain response to external stimuli using near-infrared spectroscopy (fNIRS) may become a gateway to detecting covert consciousness in clinically unresponsive patients. This is the first fNIRS study on the cortical hemodynamic response to favorite music using a frequency domain approach. The aim of this study was to identify a possible marker of cognitive response in healthy subjects by investigating variations in the oscillatory signal of fNIRS in the spectral regions of low-frequency (LFO) and very-low-frequency oscillations (VLFO). The experiment consisted of two periods of exposure to preferred music, preceded and followed by a resting phase. Spectral power in the LFO region increased in all the subjects after the first exposure to music and decreased again in the subsequent resting phase. After the second music exposure, the increase in LFO spectral power was less distinct. Changes in LFO spectral power were more proGfirst music exposure and the repetition-related habituation effect strongly suggest a cerebral origin of the fNIRS signal. Recognition of typical patterns of brain response to specific environmental stimulation is a required step for the concrete validation of a fNIRS-based diagnostic tool.

Functional NIRS to detect covert consciousness in neurocritical patients

“…Moreover, music-based interventions are already employed in patients with disorders of consciousness and are thought to have a beneficial effect during neurorehabilitation by increasing neuroplasticity (Sihvonen et al, 2017, Verger et al, 2014. In a previous study with healthy subjects, we found an increase of spectral power of low-frequency oscillation (LFO) within HbO2signal measured by fNIRS, after exposure to preferred music, followed by a decrease in LFO spectral power after the end of music (Bicciato et al, 2021). Therefore, for the current study, hemodynamic response to music measured was defined by this pattern of change in LFO spectral power during and after music exposure.…”

“…We compared the cohort of patients to a group of 6 healthy controls. The data of the control group has been previously published (Bicciato et al, 2021). The study was approved by the local ethics committee.…”

“…Analyses were performed in MATLAB_R2019b (Mathworks, Natick MA, USA). Although both O2Hb and HHb signals were obtained, we only chose O2Hb to perform statistical analyses due to its superior signal-to-noise ratio (Bicciato et al, 2021, Wolf et al, 2011. Raw fNIRS data were set to zero-line and band-pass filtered between 0.007 and 0.4 Hz (filter order = 8, type = Butterworth).…”

“…The filtering removed physiological noise such as respiration and cardiac pulsation. The low bandpass filter of 0.4 Hz was chosen minimize the loss of information and was consistent with the value used in the previous study with healthy subjects (Bicciato et al, 2021), however a low pass filter of 0.4 Hz may have included some noise due to respiratory activity (normal respiratory rate in healthy adults 16-20 breaths per minute). To exclude that our results have been driven by different respiratory rate among the group of patients we recalculated them also with a low pass filter of 0.2 Hz.…”

“…As LFO.Ratio is expressed in a natural logarithmic form positive value indicate an increase in LFO spectral power, while negative values indicate a decrease. The values of LFO.Ratio of the healthy subjects had previously been published (Bicciato et al, 2021).…”