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Previous work investigating frequency encoding mechanisms in human auditory cortex has provided evidence that latency of the auditory evoked M100 is strongly proportional to frequency, with low frequency (100^200 Hz) tones associated with B30 ms longer latencies than mid-range frequency (1^2 kHz) tones. Motivated by pervasive speech and auditory perception de¢cits observed in autism spectrum disorder, we evaluated M100 frequency dependence in children with autism disorder and typically developing controls.Results indicate that for control children, the dynamic range of frequency modulation was similar to previous reports for healthy adults. Children with autism had a much reduced range of modulation in right hemisphere sites. Findings indicate that frequency encoding mechanisms may follow a di¡erential maturational path in autism spectrum disorder.

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Purpose: determine if language disorder in children with autistic disorder (AD) corresponds to abnormalities in hemispheric asymmetries in auditory language cortex. Methods: MRI morphometric study in children with AD (n = 50) to assess hemispheric asymmetries in auditory language cortex. A key region of interest was the planum temporale (PT), which is larger in the left hemisphere in most healthy individuals. Results: (i) Heschl’s gyrus and planum polare showed typical hemisphere asymmetry patterns; (ii) posterior Superior Temporal Gyrus (pSTG) showed significant rightward asymmetry; and (iii) PT showed a trend for rightward asymmetry that was significant when constrained to right-handed boys (n = 30). For right-handed boys, symmetry indices for pSTG were significantly positively correlated with those for PT. PT asymmetry was age dependent, with greater rightward asymmetry with age. Conclusions: results provide evidence for rightward asymmetry in auditory association areas (pSTG and PT) known to subserve language processing. Cumulatively, our data provide evidence for a differing maturational path for PT for lower functioning children with AD, with both pre- and post-natal experience likely playing a role in PT asymmetry.Electronic supplementary materialThe online version of this article (doi:10.1007/s11689-009-9010-2) contains supplementary material, which is available to authorized users.

MEG studies have shown that the timing (latency) of the evoked response that peaks approximately 100 ms post-stimulus onset (M100) decreases as frequency increases for sinusoidal tones. We investigated M100 latency using a continuum of synthesized vowel stimuli in which the dominant formant frequency increases from 250 Hz (perceived /u/) to 750 Hz (perceived /a/) in 50 Hz steps. While M100 latency did vary inversely with formant frequency overall, frequency modulation was flattened within each vowel category. However, for mid-continuum ambiguous tokens (i.e. those with increased reaction time/decreased accuracy in the concurrent behavioral identification task), M100 reverted to formant frequency differences, agreeing with previous findings of frequency-dependence. A theory is proposed in which phonological categorization emerges from specific spatial distribution of frequency-tuned neurons.

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Asymmetry in single equivalent dipole modeling of the late neuromagnetic field evoked by simple speech sounds correlates with hemispheric language dominance, although not to the degree necessary for individual clinical predictions. With further development, MS imaging of simple language tasks may be used preoperatively to predict language dominance and even to identify or constrain the intraoperative search for likely sites of essential language cortex.

Efforts to correlate peripheral neurophysiologic function with perceptional deficits seen in autistic disorder (AD) have resulted in mixed findings, reflecting the high degree of heterogeneity observed in these individuals. We used the auditory brainstem response to study the effect of stress (high click presentation rate) on the auditory system in 20 children with AD (7-13 years) and 20 age-matched typically developing (TD) children. We report latency prolongations in children with AD vs. TD at waves I, III, and V that differed by ear of presentation: overall, left ear showed significant prolongations by group while right ear did not. The 'stressed' condition produced prolongations for both groups at each wave. At wave V, children with AD showed significant prolongations vs. TD, particularly for the right ear. For children with AD, wave V latency prolongations corresponded to language outcome as measured by VIQ, with longer prolongations associating with lower VIQ. Preliminary results provide evidence for reduced synaptic efficiency in auditory pathways in children with AD, which may form the neural bases for sensory reactivity and language impairment.