title: Simultaneously-evoked auditory potentials (SEAP): A new method for concurrent measurement of cortical and subcortical auditory-evoked activity.
abstract: Recent electrophysiological work has evinced a capacity for plasticity in subcortical auditory nuclei in human listeners. Similar plastic effects have been measured in cortically-generated auditory potentials but it is unclear how the two interact. Here we present Simultaneously-Evoked Auditory Potentials (SEAP), a method designed to concurrently elicit electrophysiological brain potentials from inferior colliculus, thalamus, and primary and secondary auditory cortices. Twenty-six normal-hearing adult subjects (mean 19.26 years, 9 male) were exposed to 2400 monaural (right-ear) presentations of a specially-designed stimulus which consisted of a pure-tone carrier (500 or 600 Hz) that had been amplitude-modulated at the sum of 37 and 81 Hz (depth 100%). Presentation followed an oddball paradigm wherein the pure-tone carrier was set to 500 Hz for 85% of presentations and pseudo-randomly changed to 600 Hz for the remaining 15% of presentations. Single-channel electroencephalographic data were recorded from each subject using a vertical montage referenced to the right earlobe. We show that SEAP elicits a 500 Hz frequency-following response (FFR; generated in inferior colliculus), 80 (subcortical) and 40 (primary auditory cortex) Hz auditory steady-state responses (ASSRs), mismatch negativity (MMN) and P3a (when there is an occasional change in carrier frequency; secondary auditory cortex) in addition to the obligatory N1-P2 complex (secondary auditory cortex). Analyses showed that subcortical and cortical processes are linked as (i) the latency of the FFR predicts the phase delay of the 40 Hz steady-state response, (ii) the phase delays of the 40 and 80 Hz steady-state responses are correlated, and (iii) the fidelity of the FFR predicts the latency of the N1 component. The SEAP method offers a new approach for measuring the dynamic encoding of acoustic features at multiple levels of the auditory pathway. As such, SEAP is a promising tool with which to study how relationships between subcortical and cortical processes change through early development and auditory learning as well as by hearing loss and aging.
authors.affiliation: Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Christopher
authors.initials: C
authors.lastname: Slugocki
authors.affiliation: Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bosnyak
authors.affiliation: Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, Ontario, Canada; Rotman Research Institute, Baycrest Hospital, Toronto, Ontario, Canada. Electronic address: LJT@mcmaster.ca.
authors.forename: Laurel J
authors.initials: LJ
authors.lastname: Trainor
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D001301:Audiometry, Pure-Tone; D001303:Auditory Cortex / Q000502:physiology*; D001306:Auditory Pathways / Q000502:physiology; D004569:Electroencephalography; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D006801:Humans; D007245:Inferior Colliculi / Q000502:physiology*; D008297:Male; D009473:Neuronal Plasticity; D012815:Signal Processing, Computer-Assisted; D013788:Thalamus / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: Auditory state-state response (ASSR); Auditory-evoked potentials (AEP); Brainstem; Cortex; Corticofugal; Frequency-following response (FFR)