Auditory event-related potentials (ERPs) and mismatch negativity (MMN) in healthy children and those with attention-deficit or Tourette/tic symptoms

Abstract

Introduction: This study compared 5 auditory, event-related potential (ERP) components (from P1 to P3, 50 to 500 ms post stimulus) after 3 tones differing in pitch and in rarity presented to three groups of children. The mismatch negativity (MMN), the ERP trace of auditory working memory for deviant stimuli was also studied. Methods: Topographic recordings were derived from 19 electrodes over the scalp of 12 children with attention-deficit/hyperactivity disorder (ADHD): mean 10.2 years-of age), 12 healthy controls matched for age, and 10 with chronic complex Tic- or Tourette syndrome (TS), who also showed symptoms of attention-deficit. Results: Four major effects are reported: a) Shorter ERP latencies were evident in ADHD children as early as 100 ms after the stimulus; b) Both ADHD and TS children showed larger P2 component amplitudes than the controls with their maxima shifted more anteriorly; c) Frontal MMN was not significantly different between ADHD and healthy controls, but the normalised data showed a left-sided distribution in the ADHD group and a right-sided distribution in the normal children. Maxima for TS children was unusually more posterior. (In adults the distribution is normally frontal and bilateral.) d) ADHD patients did not show the usual right-biased P3 asymmetric distribution (nor a frontal vs. parietal latency difference). Conclusions: These results suggest that ADHD children process information faster from the early N1 (c. 100 ms) stage. Both groups of children with attention-deficit symptoms showed a marked enhancement of the inhibitory phase of processing in the auditory cortex marked by P2. That this is shown even after a standard stimulus indicates an increased likelihood of unimportant stimuli being further processed and coming to control behaviour, while stimuli competing for attention are suppressed. Later indices of processing (N2-P3) showed a frontal impairment (TS), especially in the right hemisphere (ADHD) that are suggested to be indicative of anomalous timing in the development of frontal function.