Neural origins of the acoustic change complex auditory evoked potential: Topographical maps and source localization in the auditory cortex.

OBJECTIVE: In general, the neural origins of the 'acoustic change complex' (ACC) are attributed to the auditory cortex, based on measurements performed on the brain response to the 'onset' of a sound, rather than a 'change' response per se. AIMS: (1) to produce ACC topographical maps via high-density electroencephalography (EEG) multi-electrode arrays to visualise brain activity across the entire scalp; (2) to perform source localization specifically on the ACC. DESIGN: ACC responses were recorded via 128 channel EEG from 18 normal hearing adults. Sound stimulus: 1 kHz pure tone containing a 10% frequency change, 3000 ms pre-transition duration. 'Onset' and 'ACC' topographical maps were generated. Source localization was performed using MNE-Python and a standard linearly constrained minimum variance (LCMV) beamforming method. RESULTS: Classic P1-N1-P2 waveforms were observed for both the onset response and ACC by plotting voltage against time. The sound onset elicited a faster response than the sound change. ACC topographical maps resembled those of the onset response; P1, N1 and P2 peaks were identified, and central electrodes gave robust responses. ACC and onset response source time courses revealed bilateral localization of the N1 peaks in the auditory cortex. CONCLUSIONS: Topographical maps represent a useful means to explore the fidelity and temporal dynamics of the ACC. Results confirmed that neural origins of the ACC reside bilaterally in the auditory cortex. Interestingly, source localization of the ACC showed a similar spatial distribution to the onset response, suggesting similar neural generators, although further research is required for deeper clarification.