Evidence for a neurophysiologic auditory deficit in children with benign epilepsy with centro-temporal spikes.

Benign focal epilepsy in childhood with centro-temporal spikes (BECTS) is one of the most common forms of epilepsy. Recent studies have questioned the benign nature of BECTS, as they have revealed neuropsychological deficits in many domains including language. The aim of this study was to investigate whether the epileptic discharges during the night have long-term effects on auditory processing, as reflected on electrophysiological measures, during the day, which could underline the language deficits. In order to address these questions we recorded base line electroencephalograms (EEG), sleep EEG and auditory event related potentials in 12 children with BECTS and in age- and gender-matched controls. In the children with BECTS, 5 had unilateral and 3 had bilateral spikes. In the 5 patients with unilateral spikes present during sleep, an asymmetry of the auditory event related component (P85-120) was observed contralateral to the side of epileptiform activity compared to the normal symmetrical vertex distribution that was noted in all controls and in 3 the children with bilateral spikes. In all patients the peak to peak amplitude of this event related potential component was statistically greater compared to the controls. Analysis of subtraction waveforms (deviant - standard) revealed no evidence of a mismatch negativity component in any of the children with BECTS. We propose that the abnormality of P85-120 and the absence of mismatch negativity during wake recordings in this group may arise in response to the long-term effects of spikes occurring during sleep, resulting in disruption of the evolution and maintenance of echoic memory traces. These results may indicate that patients with BECTS have abnormal processing of auditory information at a sensory level ipsilateral to the hemisphere evoking spikes during sleep.

Auditory event-related potentials in the assessment of auditory processing disorders: a pilot study.

The aim of this pilot study was to investigate whether children with a suspected auditory processing disorder (sAPD) in the presence of normal hearing, differ significantly from normal age-matched controls on particular parameters of auditory event-related potentials. We assessed nine children (mean age 9.5 years) in whom the clinical profile and the results in a screening test for auditory processing disorder (SCAN/SCAN-A) suggested the presence of an auditory processing disorder, and nine age-matched normal control subjects, using auditory event-related potentials (ERP) to phonemes/ba/(standard) and/da/(deviant). Analysis of the auditory ERP recordings revealed an enlarged P85 - 120 and attenuated N1 and P2 in all sAPD children compared to controls. We also found significantly increased N1 peak latency, and a larger peak to peak amplitude of the P85 - 120-N1 and P2-N2 and smaller peak to peak amplitude of the N1-P2 in the sAPD children. Subtraction of the standard auditory ERP from the deviant revealed a mismatch negativity with no significant differences in duration, peak or onset latency between the control subjects and sAPD. Our results indicate that neurophysiological measures may identify a group of children with specific problems suggestive of an auditory processing disorder in the absence of an obvious structural or functional lesion who warrant further study in order to assess whether these findings reflect delayed CNS myelination.

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study.

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's area 45) is involved in early stages of processing repeating sounds and sound changes.