Judith A. Kreuzer

Maturation of mismatch negativity in typically developing infants and preschool children.

Objective 1) To determine whether an adult-like mismatch negativity (MMN) can be reliably elicited in typically developing awake infants and preschool children, and if so 2) to examine whether maturational changes exist in MMN latency and amplitude. Design Two experiments were designed to elicit MMN using an “oddball” paradigm. In Experiment 1, a 1000-Hz tone served as the standard stimulus and a 1200-Hz tone as the deviant. In Experiment 2, a 1000-Hz standard stimulus and a 2000-Hz deviant were presented. Infants’ ages ranged from 2 to 47 and 3 to 44 mo in Experiments 1 and 2, respectively. Results In Experiment 1, a negativity was not elicited in the majority of the infants and preschoolers tested. In Experiment 2, a negativity was reliably elicited in the infants and preschoolers across all ages. A significant negative correlation was observed between age and latency, but not for age and amplitude for this negativity. This negativity was found to decrease at a rate of 1 msec/mo. Infants younger than 12 mo of age showed a significantly larger positivity to the deviant than to the standard between 150–300 and 200–300 msec in Experiments 1 and 2, respectively. Conclusions The discriminative processes indexed by MMN in response to frequency changes are immature in infants and preschool children. Although there is convincing evidence that the negativity elicited in Experiment 2 is an immature MMN, the possibility that it may be an “obligatory effect” indexing recovery from refractoriness cannot be ruled out at this time. The results from these experiments suggest that the MMN component has limited use as a clinical tool at this time for infants and young children.

Developmental studies and clinical application of mismatch negativity : problems and prospects

There is wide interest in the clinical application of mismatch negativity (MMN) to assess discriminative capabilities in individuals whose auditory capacities are difficult to determine, including infants, young children and those with severe cognitive impairment. Before MMN can be used as a clinical electrophysiologic measure, it is necessary to establish that it can be reliably elicited in normal individuals. This chapter describes a detailed analysis of MMN recorded in a group of healthy 8-yr-old children to assess intrasubject and intersubject reliability of the response. We conclude that although statistically reliable results can be obtained with group data, and perhaps even in individuals when large numbers of stimuli can be delivered, the unfavorable signal to noise ratio of individual MMN data currently limits its clinical applicability. Suggestions for approaches to surmount these difficulties are presented for its eventual clinical usefulness.

Cortical responses to speech sounds and their formants in normal infants: maturational sequence and spatiotemporal analysis

Cortical auditory evoked potentials (AEPs) to the synthesized syllables [da[ and [ta[ and to the isolated 3 formants of [da[ were obtained from 32 normal infants studied at monthly intervals from birth through 3 months and at 6 months of age. A bilateral array of 16 electrodes referenced to the mid-occiput permitted a topographic analysis of the cortical AEPs at selected latencies. A differential maturational sequence was seen: a predominantly negative cortical AEP wave form became positive, first over the frontocentral region (around term), and then over the temporal region (at 1-2 months). The timing of these electrophysiological changes coincides with a differential anatomical maturational sequence in the auditory cortex, as myelination and synaptogenesis are more advanced in primary than secondary auditory areas at term. All infants in this study followed this developmental sequence. However, there was no systematic effect of the center frequency of the formant stimuli on the maturational level of their respective cortical AEPs, suggesting a relative maturational equivalence in those regions of auditory cortex responding to stimuli across the frequency range present in human speech. In term infants, an initial midline positivity and bitemporal negativities were asynchronous in their peak and offset latencies. suggesting independent generators for each of these components. In infants from 3 to 6 months of age, cortical AEP wave forms consisted of 2 initial positive peaks followed by a negative peak. While the wave forms were similar over midline and lateral scalp, spatiotemporal analysis revealed differences in the latency of onset, duration and in the spatial extent of these components, again suggesting that 2 bilateral, temporally overlapping generators contribute to the cortical AEP. No systematic topographic difference was observed in the cortical AEPs elicited by each of the 3 formants, which differed in center frequencies.

Differential maturation of cortical auditory evoked potentials to speech sounds in normal fullterm and very low-birthweight infants

Cortical auditory evoked potentials (AEP) to the consonant‐vowel syllables /da/ and /ta/ and 800Hz tone were recorded at 40 weeks post‐conceptional age and at one, two and three months after term in normal fullterm and very low‐birthweight infants. As a group, the very low‐birthweight infants exhibited significantly less mature AEPs to consonant‐vowel syllables than the normal‐birthweight infants at 40 weeks post‐conceptional age. Consistent but statistically non‐significant differences also were found for tones at 40 weeks post‐conceptional age, and for all stimuli at one and two months after term. By three months, all the infants exhibited mature AEP morphology and topography.

Maturation of mismatch negativity in school-age children.

Objective: Event‐related potentials were recorded to investigate the maturation of auditory processing in school‐age children. Design: The mismatch negativity (MMN) was obtained in an oddball tone discrimination paradigm in 66 school‐age children and 12 adults. In the childrens data, a prominent negativity to both the standard and deviant tone, peaking around 200 msec, was observed, and compared with the N1 auditory evoked potential component. Results: The MMN was found to decrease with latency by 11 msec/yr from 4 to 10 yr of age. No developmental change in MMN amplitude was seen from 4 to 10 yr of age. However, the MMN amplitude was significantly smaller in adults than in children. The prominent negativity in children was significantly later than the adult N1 component, and did not change in latency from 4 to 10 yr of age. This finding adds to a body of evidence suggesting that this prominent negativity and the adult N1 are not the same component. The magnitude of the prominent negativity in children decreased slightly with age. Conclusion: Changes in the timing of the brain discriminative response, MMN, suggest systematic maturational changes in auditory processing.

Maturation of mismatch negativity: A scalp current density analysis

Objective Auditory evoked potentials provide the opportunity to better understand the central processing of auditory stimuli, which is the basis of speech and language perception. The purpose of this study was to examine maturational changes in the topography of one of these auditory evoked potentials, the mismatch negativity (MMN), using scalp current density (SCD) analysis. Design Subjects were children ages 4 to 11 yr (N = 53), and adults (N = 12). Stimuli were 85 dB peSPL 1000 Hz standard tones and 1200 Hz deviant tones (deviant probability = 0.15). Auditory evoked potentials were recorded using surface electrodes placed at 32 locations on the head while subjects ignored the stimuli by watching a silent video. Results Significant maturational changes in topography of MMN were seen over frontal and left lateral sites. Conclusions Differences in MMN for the children compared to adults indicate that the MMN generators or their orientation, and thus the neural processes underlying discrimination of simple tones, are not yet mature by 11 yr of age.

Electrophysiologic Correlates of Semantic Classification in Autistic and Normal Children

This study tested the hypothesis that language processing by high-functioning, verbal autistic children is less influenced by global semantic context than that of their normal peers. Behavioral measures of reaction time and error rate were employed to evaluate speed and accuracy in classifying auditorally presented words according to a superordinate category label. In addition, an electrophysiologic index of semantic expectancy, the N4 component of auditory event-related potentials, was used to assess the relative levels of activation of in-category versus out-of-category words. Age and nonverbal IQ matched groups of 8 normal and 8 nonretarded autistic children were studied. The age range for the autistic participants was 7 years 4 months to 10 years 8 months (M = 8 years 10 months) and for the normal participants was 7 years 6 months to 10 years 11 months (M = 9 years 1 month). Participants responded with a finger lift to any word belonging to the animal category. The instruction set and stimulus list co...

Temporal integration: intentional sound discrimination does not modulate stimulus-driven processes in auditory event synthesis.

OBJECTIVE Our previous study showed that the auditory context could influence whether two successive acoustic changes occurring within the temporal integration window (approximately 200ms) were pre-attentively encoded as a single auditory event or as two discrete events (Cogn Brain Res 12 (2001) 431). The aim of the current study was to assess whether top-down processes could influence the stimulus-driven processes in determining what constitutes an auditory event. METHODS Electroencepholagram (EEG) was recorded from 11 scalp electrodes to frequently occurring standard and infrequently occurring deviant sounds. Within the stimulus blocks, deviants either occurred only in pairs (successive feature changes) or both singly and in pairs. Event-related potential indices of change and target detection, the mismatch negativity (MMN) and the N2b component, respectively, were compared with the simultaneously measured performance in discriminating the deviants. RESULTS Even though subjects could voluntarily distinguish the two successive auditory feature changes from each other, which was also indicated by the elicitation of the N2b target-detection response, top-down processes did not modify the event organization reflected by the MMN response. CONCLUSIONS Top-down processes can extract elemental auditory information from a single integrated acoustic event, but the extraction occurs at a later processing stage than the one whose outcome is indexed by MMN. SIGNIFICANCE Initial processes of auditory event-formation are fully governed by the context within which the sounds occur. Perception of the deviants as two separate sound events (the top-down effects) did not change the initial neural representation of the same deviants as one event (indexed by the MMN), without a corresponding change in the stimulus-driven sound organization.