UBC Theses and Dissertations
Cortical auditory evoked potentials : is the acoustic change complex a transient onset response in disguise? Cheema, Sonay
Cortical auditory evoked potentials (CAEPs) are believed to reflect the neural discrimination and encoding of sound. These responses include obligatory evoked potentials including the P1-N1-P2 complex. The P1-N1-P2 response that occurs at the beginning of the stimulus presentation is called the onset response, while the P1-N1-P2 response that occurs at the re-introduction of sound, such as after a silent interval (gap) in noise stimulus, is called the auditory change complex (ACC). Though the onset and the ACC responses are evoked by the same auditory stimulus, the matter of whether they are mediated by the same physiological mechanisms is met with inconsistency in the cortical auditory evoked response literature. The current trend is to refer to the responses as different events, indicating a possible belief that the source generators are also different. This retrospective study of 35 participants’ datasets tested the null hypothesis that both the onset and ACC responses are generated from the same neural location. Dipole source modelling was conducted on existing CAEP gap-detection data to determine each response’s source generators. Results showed dipoles for the ACC were significantly located more posteriorly (0.4±1 mm) than dipoles for onset P1-N1-P2 response, thus rejecting the null hypothesis. These unexpected results provide evidence that the transient onset and ACC responses are likely undergoing differing underlying neural processes in response to acoustic changes in the environment. These findings allow researchers to more confidently refer to both the onset and ACC responses as different events, thereby diminishing confusion and increasing accuracy of future discussions about and clinical applications with CAEPs.
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