Preliminary Study of Auditory Brainstem and Middle Latency Evoked Potentials In a Passive Oddball Paradigm

• ¹ Department of Psychiatry and Clinical Psychobiology, University of Barcelona, Spain

Humans are able to detect unexpected new events in the auditory environment. The neural correlates of change detection are commonly studied through the oddball paradigm. Auditory event-related studies indicate that oddballs reliably elicit a negative potential approximately 100-300 ms after the stimulus onset called mismatch negativity (MMN) response. Besides the temporal and possible frontal and parietal contribution to MMN generation, few animal studies reported a MMN like-response in the non-primary thalamus and inferior colliculus. In humans, an investigation of the thalamic and brainstem auditory structure involvement in auditory novelty detection generation is yet lacking.

The goal of the current pilot study is to investigate the effect of auditory frequency deviance detection in the time range of the auditory brainstem (ABR) and middle latency (MLR) responses using an oddball paradigm. Forty ms broadband noise bandpass-filtered, ranging from 500 to 3000 Hz in steps of 500 Hz, were delivered with a stimulus onset asynchrony of 86 ms at 100 dB SPL to the left ear. White noise was presented to the right ear at 70 dB SPL to mask any background noise. Three blocked conditions were presented: an oddball block with a deviant probability of p=0.2; (b) a reverse oddball block; and (c) a control block in which stimuli of five different frequency bands were presented randomly, each with a probability of p=0.2. ABR and MLR responses were recorded from 5 participants at Cz and mastoid electrodes using right ear lobe as the reference.

The latency and amplitude of the waves V, Na, Pa, Nb were studied in deviant stimuli in comparison to physically identical standard and control stimuli. Our results indicate the absence of significant differences in the ABR. In the MLR time range differences were obtained for the Pa component (t(4) = 3.05, p < .038) at a latency window of 29 to 33 ms, for deviants compared to standards for the 1000-1500 Hz frequency range. This might reflect a probability-sensitive index, clearly preceding MMN, even though not at the level of the auditory brainstem. Results are in line with the findings of Grimm et al., 2009, supporting the validity of the use of animal models in the search of the human correlates of novelty detection.