Stimulus-evoked phase-locked activity along the human auditory pathway strongly varies across individuals

Robin Gransier,Michael Hofmann,Jan Wouters,Astrid Van Wieringen

doi:10.1038/s41598-020-80229-w

Abstract

Phase-locking to the temporal envelope of speech is associated with envelope processing and speech perception. The phase-locked activity of the auditory pathway, across modulation frequencies, is generally assessed at group level and shows a decrease in response magnitude with increasing modulation frequency. With the exception of increased activity around 40 and 80 to 100 Hz. Furthermore, little is known about the phase-locked response patterns to modulation frequencies ≤ 20 Hz, which are modulations predominately present in the speech envelope. In the present study we assess the temporal modulation transfer function (TMTFASSR) of the phase-locked activity of the auditory pathway, from 0.5 to 100 Hz at a high-resolution and by means of auditory steady-state responses. Although the group-averaged TMTFASSR corresponds well with those reported in the literature, the individual TMTFASSR shows a remarkable intersubject variability. This intersubject variability is especially present for ASSRs that originate from the cortex and are evoked with modulation frequencies ≤ 20 Hz. Moreover, we found that these cortical phase-locked activity patterns are robust over time. These results show the importance of the individual TMTFASSR when assessing phase-locked activity to envelope fluctuations, which can potentially be used as a marker for auditory processing.

Highlights

Phase-locking to the temporal envelope of speech is associated with envelope processing and speech perception
In vivo studies in animals have shown that earlier neural regions in the ascending auditory pathway are responsive to higher modulation frequencies whereas cortical regions predominately respond to lower modulation frequencies10. fMRI studies in humans have shown that all neural regions across the ascending human auditory pathway are responsive to amplitude modulations (AM) sounds ranging from 4 to 256 Hz, subcortical regions have a greater activation to modulation frequencies > 32 Hz, whereas cortical regions have more activation to modulation frequencies < 32 Hz11,12
In the present study we investigated the phase-locked activity along the auditory pathway at a high resolution to AM sounds with modulation frequencies between 0.5 and 100 Hz in a homogeneous group of normal-hearing adults

Summary

Introduction

Phase-locking to the temporal envelope of speech is associated with envelope processing and speech perception. With the exception of increased activity around 40 and 80 to 100 Hz. little is known about the phase-locked response patterns to modulation frequencies ≤ 20 Hz, which are modulations predominately present in the speech envelope. In the present study we assess the temporal modulation transfer function (TMTFASSR) of the phase-locked activity of the auditory pathway, from 0.5 to 100 Hz at a high-resolution and by means of auditory steady-state responses. The group-averaged TMTFASSR corresponds well with those reported in the literature, the individual TMTFASSR shows a remarkable intersubject variability This intersubject variability is especially present for ASSRs that originate from the cortex and are evoked with modulation frequencies ≤ 20 Hz. we found that these cortical phase-locked activity patterns are robust over time.

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