SOUND INTENSITY-DEPENDENT CORTICAL ACTIVATION: CORRELATING AUDITORY
EVOKED POTENTIALS WITH FNIRS TOPOGRAPHIES.
Abstract
Recent studies combining electroencephalography (EEG) and functional
near-infrared spectroscopy (fNIRS) have shown promising results by
correlating EEG characteristics with the spatial information provided by
fNIRS. The present study aims to analyze the topographical effect of
auditory stimulus intensity on cortical activation using fNIRS and to
correlate this hemodynamic response with auditory evoked potentials
(AEPs) P1, N1, and P2 and their possible habituation. Forty volunteers
(13 males, 27 females; mean age = 22.27 ± 3.96 years) participated in
this study. The experimental section involved the presentation of
complex tones of different intensities (50-, 70-, and 90-dB SPL)
including 7 different frequencies (400, 850, 1150, 1650, 1950, 2450,
2750 Hz), in blocks of five stimuli, while EEG and fNIRS signals were
recorded. Our results indicate that increasing sound intensity led to
amplitude changes in AEPs, and enhanced neural recruitment in auditory
and prefrontal cortices, as analyzed by fNIRS. Correlation analyses
suggest a prefrontal source for the P2 component. In addition, the
observed correlation between the habituation index and specific
prefrontal cortex channels in the inferior and superior frontal gyri
would suggest the involvement of cognitive resources in the habituation
process to block stimuli. These findings provide insight into the
relationship between auditory stimulus intensity and neural engagement,
with potential implications for understanding auditory perception in
both healthy and clinical populations.