title: Two-channel recording of auditory-evoked potentials to detect age-related deficits in temporal processing.
abstract: Auditory brainstem responses (ABRs), and envelope and frequency following responses (EFRs and FFRs) are widely used to study aberrant auditory processing in conditions such as aging. We have previously reported age-related deficits in auditory processing for rapid amplitude modulation (AM) frequencies using EFRs recorded from a single channel. However, sensitive testing of EFRs along a wide range of modulation frequencies is required to gain a more complete understanding of the auditory processing deficits. In this study, ABRs and EFRs were recorded simultaneously from two electrode configurations in young and old Fischer-344 rats, a common auditory aging model. Analysis shows that the two channels respond most sensitively to complementary AM frequencies. Channel 1, recorded from Fz to mastoid, responds better to faster AM frequencies in the 100-700 Hz range of frequencies, while Channel 2, recorded from the inter-aural line to the mastoid, responds better to slower AM frequencies in the 16-100 Hz range. Simultaneous recording of Channels 1 and 2 using AM stimuli with varying sound levels and modulation depths show that age-related deficits in temporal processing are not present at slower AM frequencies but only at more rapid ones, which would not have been apparent recording from either channel alone. Comparison of EFRs between un-anesthetized and isoflurane-anesthetized recordings in young animals, as well as comparison with previously published ABR waveforms, suggests that the generators of Channel 1 may emphasize more caudal brainstem structures while those of Channel 2 may emphasize more rostral auditory nuclei including the inferior colliculus and the forebrain, with the boundary of separation potentially along the cochlear nucleus/superior olivary complex. Simultaneous two-channel recording of EFRs help to give a more complete understanding of the properties of auditory temporal processing over a wide range of modulation frequencies which is useful in understanding neural representations of sound stimuli in normal, developmental or pathological conditions.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN 47906, USA.
authors.forename: Aravindakshan
authors.initials: A
authors.lastname: Parthasarathy
authors.forename: Edward
authors.initials: E
authors.lastname: Bartlett
mesh_terms: D000161:Acoustic Stimulation; D000367:Age Factors; D000375:Aging; D000818:Animals; D001306:Auditory Pathways / Q000503:physiopathology*; D001307:Auditory Perception; D001309:Auditory Threshold; D016057:Evoked Potentials, Auditory, Brain Stem; D051381:Rats; D011916:Rats, Inbred F344; D011930:Reaction Time; D013997:Time Factors; D013998:Time Perception