Abstracts

Rationale: Intracranial electroencephalography (iEEG) has permitted such high temporal resolution of task-related cortical signals as to reveal ‘Onset’ and ‘Sustained’ profiles among auditory processing sites. Onset sites have been shown to be transient and consistently localized to the posterior superior temporal region (pSTR). Our work contrasting responses to speech and noise has led us to elaborate the salience detector hypothesis of auditory Onset sites (Brown EC, et al. bioRxiv doi: 10.1101/2021.04.14.439910). It is predicted that, when linguistic information is uninvolved, Onset sites show more intense recurrent intrastimulus activity upon a state change toward enhanced salience. We aim to test this hypothesis.

Methods: In subjects with iEEG electrodes in place for extra-operative seizure monitoring, we detected cortical activity during an auditory task of ~20 minutes duration. Stimuli of 2 seconds duration each include 30 questions, 10 signal correlated noise (SCN) stimuli, and 60 paired non-speech stimuli. Paired stimuli involve 20 matched pairs each of instrument and alarm sounds, consonant and dissonant piano chords, and voices and screams. Alarm sounds, dissonant chords, and screams are of increased roughness, a marker of salience, relative to their matched sound. We strictly identified auditory Onset sites as those responding with a transient increase in high gamma activity (75-110Hz) to both question and SCN stimuli. We then observed relative peak activity response within paired stimuli, focusing on the responses to the second sound in the pair relative to the first.

Results: Preliminary analysis has been completed in two adults. A total of 5 electrodes of the pSTR were identified as auditory Onset, 1 on the left and 4 on the right. Across these sites, we determined the response to paired stimuli. When instrument sounds followed alarm sounds, the average relative response to the instrument sounds was 63.4% that of the preceding alarm sound. When the alarm sound followed the instrument, the average relative response was 65.1%. When dissonant chords followed consonant chords, the average relative response was 75.1% while it was 59.5% for the opposite order. When a scream followed a voice, the average relative response was 85.5% while it was 74.1% for the opposite order. In patient 1, noted consonant chords, dissonant chords, and instrument sounds to have excited a more anterior site of the planum temporale not involved in question or SCN stimuli.

Conclusions: These preliminary findings provide an emerging picture of how stimulus salience influences auditory Onset sites. Despite a lack of statistical power to demonstrate a significant difference, in each case the recurrent Onset activity was stronger when the second stimulus was the higher salience member of a matched pair. This effect was least pronounced when an alarm sound followed an instrument sound. The musical quality of an instrument may be associated with negative feedback at auditory Onset sites similar to that of linguistic processing as described by the salience hypothesis. Further subjects will be evaluated in order to further elucidate these phenomena.

Funding: Please list any funding that was received in support of this abstract.: OHSU Tartar Trust Fellow; OHSU MRF Early Clinical Investigator.