PP1125 - MLR Characteristics in Children With and Without Dichotic Deficits

Abstract:
We compared auditory middle latency responses (MLRs) in children without dichotic deficits to those with amblyaudia (AMB) or dichotic dysaudia (DD) with respect to stimulus ear (right or left), electrode site (C3 or C4), and stimulus rate (slow or fast). Children with DD generally produced shorter latencies at the slow rate and longer latencies at the fast rate of stimulation with greater effects for the right ear. Children with AMB demonstrated longer latencies with the slow rate and larger amplitudes at C4 following left ear stimulation. Findings highlight ear and rate susceptibilities in children with different dichotic deficit patterns.

Summary:
Objective
We investigated ear, electrode, and stimulus rate effects in children with amblyaudia (AMB) and Dichotic Dysaudia (DD), a subtype of auditory processing disorder (APD), via auditory middle latency response. The MLR can be reliably used to assess auditory integrity both within ascending neural structures and across the interhemispheric pathways of the corpus callosum. Reduced amplitudes over a hemisphere, regardless of which ear was stimulated, referred to as the “electrode effect”, have been observed in patients with auditory lesions in the temporal lobe, while patients with subcortical lesions, thalamus or as low as high-brainstem, have shown “ear effect” which refers to an abnormal response evoked by stimulation of the contralateral ear only. Efforts to differentiate the response in individuals not suspected of a lesion but with auditory processing difficulties, however, have been limited and have failed to reach a consensus.

Design and study samples
MLRs were recorded to click-trains at slow vs. fast (9.1 vs. 12.1/s) rates in n=21 children with AMB, n= 7 children with DD, and n= 13 age-matched controls. Multivariate and univariate ANOVA compared MLR peak-to-peak amplitude and latency by ear, electrode, stimulus rate, and between groups.

Results
Rate effects were observed for peak-to-peak latency in children with DD and AMB that varied by ear of stimulation and by comparison to children with no dichotic deficits. Children with AMB demonstrated a significant ear effect following left ear stimulation.

Conclusions
The AMB pattern is produced when one ear performs normally and the other performs poorly during dichotic tests whereas the DD pattern is produced when both ears perform poorly. MLR ear effects appear to reflect differences in bottom-up neural processing in children with these different dichotic listening patterns. MLR rate effects may be related to differences in cortical entrainment following acoustic stimulation in children with these two dichotic deficit patterns.