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.

Predictive coding framework posits that our brain continuously monitors changes in the environment and updates its predictive models, minimizing prediction errors to efficiently adapt to environmental demands. However, the underlying neurophysiological mechanisms of these predictive phenomena remain unclear. The present study aimed to explore the systemic neurophysiological correlates of predictive coding processes during passive and active auditory processing. Electroencephalography (EEG), functional near-infrared spectroscopy (fNIRS) and autonomic nervous system (ANS) measures were analyzed using an auditory pattern-based novelty oddball paradigm. A sample of thirty-two healthy subjects was recruited. The results showed shared slow evoked potentials between passive and active conditions that could be interpreted as automatic predictive processes of anticipation and updating, independent of conscious attentional effort. A dissociated topography of the cortical hemodynamic activity and distinctive evoked potentials upon auditory pattern violation were also found between both conditions, whereas only conscious perception leading to imperative responses was accompanied by phasic ANS responses. These results suggest a systemic-level hierarchical reallocation of predictive coding neural resources as a function of contextual demands in the face of sensory stimulation. Principal component analysis permitted to associate the variability of some of the recorded signals.