Short-term plasticity in the auditory system: Differential neural responses to perception and imagery of speech and music

Abstract

Purpose: In this EEG study we sought to examine the neuronal underpinnings of short-term plasticity as a top-down guided auditory learning process. We hypothesized, that (i) auditory imagery should elicit proper auditory evoked effects (N1/P2 complex) and a late positive component (LPC). Generally, based on recent human brain mapping studies we expected (ii) to observe the involvement of different temporal and parietal lobe areas in imagery and in perception of acoustic stimuli. Furthermore we predicted (iii) that temporal regions show an asymmetric trend due to the different specialization of the temporal lobes in processing speech and non-speech sounds. Finally we sought evidence supporting the notion that short-term training is sufficient to drive top-down activity in brain regions that are not normally recruited by sensory induced bottom up processing.

Methods: 18 non-musicians partook in a 30 channels based EEG session that investigated spatio-temporal dynamics of auditory imagery of “consonant-vowel” (CV) syllables and piano triads. To control for conditioning effects, we split the volunteers in two matched groups comprising the same conditions (visual, auditory or bimodal stimulation) presented in a slightly different serial order. Furthermore the study presents electromagnetic source localization (LORETA) of perception and imagery of CV- and piano stimuli.

Results: Our results imply that auditory imagery elicited similar electrophysiological effects at an early stage (N1/P2) as auditory stimulation. However, we found an additional LPC following the N1/P2 for auditory imagery only. Source estimation evinced bilateral engagement of anterior temporal cortex, which was generally stronger for imagery of music relative to imagery of speech. While we did not observe lateralized activity for the imagery of syllables we noted significantly increased rightward activation over the anterior supratemporal plane for musical imagery.

Conclusions: Thus, we conclude that short-term top-down training based auditory imagery of music and speech prompts involvement of distinct neural circuits residing in the perisylvian cortex.