Normal Ipsilateral/Contralateral Asymmetries in Infant Multiple Auditory Steady-State Responses to Air- and Bone-Conduction Stimuli

Abstract

Objectives: Two-channel recordings of infants' airand bone-conduction auditory brainstem responses to brief tones show ipsilateral and contralateral (to the stimulated ear) asymmetries which may be used to isolate which cochlea is the primary contributor to the response. The objective of this study was to determine whether similar ipsilateral/contralateral asymmetries are also present in the air-and boneconduction "brainstem" (77 to 101 Hz) auditory steady-state responses (ASSRs) of infants.Design: Two-channel ASSRs were recorded in infants (2 to 11 mo) and adults (18 to 40 yr) with normal hearing. Multiple stimuli (carrier frequencies: 500 to 4000 Hz; amplitude/frequency modulated) were presented using a B-71 oscillator on the temporal bone or an ER3-A insert earphone. Bone-conduction ASSR amplitudes, phase delays, and thresholds were obtained for the electroencephalographic (EEG) channels ipsilateral and contralateral to the oscillator temporal-bone placement. Bone-conduction ASSRs were also obtained to the stimulus presented to the opposite temporal bone (at 40 dB HL only). Airconduction ASSR amplitudes and phase delays were obtained at 60 dB HL in each ear for the EEG channels ipsilateral and contralateral to the transducer.Results: Infants showed more ipsilateral/contralateral asymmetries in both air-and bone-conduction ASSRs compared with adults. Mean bone-conduction ASSR thresholds in infants were 13 to 15 dB higher (i.e., poorer) in the contralateral EEG channel compared with the ipsilateral EEG channel for 500 to 4000 Hz. In adults, there were no large differences (i.e., within 1 dB) between ipsilateral and contralateral ASSR thresholds. Based on ipsilateral/ contralateral threshold differences in infants, interaural attenuation for bone-conducted stimuli was estimated to be at least 10 to 30 dB for most infants. In contrast, most adults showed little interaural attenuation for bone-conducted stimuli.ASSR amplitudes are larger and phase delays are shorter in the ipsilateral EEG channel. For infants, the difference in air-conduction ASSR amplitude between EEG channels was twice that observed for adults. Infants also had greater ASSR amplitude differences between EEG channels for bone-conduction stimuli compared with adults, but the difference was less than that seen for air-conduction stimuli. For air-conduction stimuli, infants had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel. Adults showed no significant differences in air-conduction ASSR phase delay between EEG channels. For bone-conduction stimuli, both infants and adults had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel; the differences in ASSR phase delays between EEG channels were much smaller in infants compared with adults and fewer adults had absent responses in the contralateral EEG channels compared with infants (12% versus 34%). When the transducers were switched to the opposite ear/mastoid, the infant and adult ipsi...

Hemispheric Asymmetry of Auditory Steady-State Responses to Monaural and Diotic Stimulation

“…In case of monaural stimulus presentation, the ipsilateral ASSR source is then more strongly activated than the contralateral source (Herdman et al 2002), resulting in stronger ipsilateral scalp recorded responses. This is consistent with previous ASSR studies reporting smaller or even absent 80 Hz ASSRs contralateral to the stimulus (Poelmans et al 2012;Small and Stapells 2008;van der Reijden et al 2005).…”

Auditory steady-state responses to bone conduction stimuli in children with hearing loss

“…Contralateral AC masking was presented via insert earphones at the same intensity as the BC stimulation. The appropriate amount of clinical masking for BC stimuli in infants is not currently known, but a recent study has reported interaural attenuation for BC ASSR in infants to be higher than in adults, with at least 10-30 dB attenuation across 0.5-4 kHz [15].…”

“…Another recent study by Small and Stapells investigated the ipsi/contralateral asymmetries in BC ASSR recordings in infants younger than 11 months of age [15]. The findings indicated significantly larger asymmetries for infants than for adults, with individual infants exhibiting at least 10-30 dB of interaural attenuation for BC ASSR compared to no more than 10 dB in adults.…”

“…Studies utilizing BC ASSR in infants are scarce and have only been reported by Cone-Wesson and colleagues, who used a sensorineural acuity level technique (SAL), and by Small and colleagues who used the multiple ASSR technique [12][13][14][15]. The SAL 0.25 kHz, 39% of thresholds were at the minimum level of spurious response occurrence.…”

“…The findings indicated significantly larger asymmetries for infants than for adults, with individual infants exhibiting at least 10-30 dB of interaural attenuation for BC ASSR compared to no more than 10 dB in adults. The greater interaural attenuation in infants is attributed to the neuromaturational state of the brainstem and the reduced efficiency of sound transmission across the infant skull with its membraneous unfused sutures [15][16][17]. The authors recommend that a 2-channel ASSR system may be used to isolate the cochlea from which the BC response occurs by examining the ipsi/contra asymmetries [15].…”