Brainstem evoked potentials in learning disabled children

Development of auditory phase-locked activity for music sounds

The auditory cortex undergoes functional and anatomical development that reflects specialization for learned sounds. In humans, auditory maturation is evident in transient auditory-evoked potentials (AEPs) elicited by speech or music. However, neural oscillations at specific frequencies are also known to play an important role in perceptual processing. We hypothesized that, if oscillatory activity in different frequency bands reflects different aspects of sound processing, the development of phase-locking to stimulus attributes at these frequencies may have different trajectories. We examined the development of phase-locking of oscillatory responses to music sounds and to pure tones matched to the fundamental frequency of the music sounds. Phase-locking for theta (4-8 Hz), alpha (8-14 Hz), lower-to-mid beta (14-25 Hz), and upper-beta and gamma (25-70 Hz) bands strengthened with age. Phase-locking in the upper-beta and gamma range matured later than in lower frequencies and was stronger for music sounds than for pure tones, likely reflecting the maturation of neural networks that code spectral complexity. Phase-locking for theta, alpha, and lower-to-mid beta was sensitive to temporal onset (rise time) sound characteristics. The data were also consistent with phase-locked oscillatory effects of acoustic (spectrotemporal) complexity and timbre familiarity. Future studies are called for to evaluate developmental trajectories for oscillatory activity, using stimuli selected to address hypotheses related to familiarity and spectral and temporal encoding suggested by the current findings.

Middle latency response in children with learning disabilities: preliminary findings

The objective of this investigation was to determine if auditory middle latency responses (MLR) obtained from children with learning disabilities (LD) differ from those obtained from children without LD. Simultaneous recordings of auditory brainstem and middle latency responses were obtained in both vertex-ipsilateral (V-I) and vertex-contralateral derivations (V-C) in 22 children (11 LD and 11 normal) in the age range of eight to twelve years whose peripheral hearing was within normal limits to bilateral. The results indicate that for specific recording conditions, the latencies of middle latency responses differ significantly between children with LD and a normal group of children.

Computer tomography in children with electrophysiological abnormalities

A computed tomography examination was carried out in a group of 43 children, of whom 15 had learning disabilities (LD). Children were selected with electrophysiological abnormalities in the routine EEG, in the quantitative EEG analysis and/or in the visual cortical and auditory brainstem evoked responses. Seven children, 1 control and 6 LD, had abnormalities in the computed tomography. The most frequent localization of the lesion was the left temporal lobe. This localization might explain the origin of the learning disorder, since the left temporal lobe is involved in reading and writing processes. There was a great concordance between the anatomical localization of the lesion by the computed tomography and the place of electrical abnormalities in the quantitative EEG and the visual evoked responses. These results strongly support the indication of a computed tomography examination in LD children.