Nicole Bruneau

Maturation of frontal and temporal components of mismatch negativity (MMN) in children.

The mismatch negativity (MMN) response of auditory ERPs in adults appears to result from several overlapping components involving both frontal and temporal brain areas. Our aim was to test whether a similar configuration could be observed in children, and to examine the maturation rates of the different components. MMN (standard tones: 1000 Hz, deviants: 1100 Hz) was recorded from 28 scalp electrodes in 24 healthy children aged from 5 to 10 and in eight adults for comparison. Scalp current density analysis revealed both temporal and frontal components in children of all ages as well as in adults. Moreover the amplitudes of the temporal components were significantly greater in children than in adults, whereas the frontal components were similar at all ages. The results strongly suggest that MMN is mediated by at least two separate neural systems, and that the frontal system matures earlier than the sensory-specific system.

Cortical auditory processing and communication in children with autism: electrophysiological/behavioral relations

The purpose of the present study was to investigate the relations between late auditory evoked potentials (AEPs) recorded at temporal sites (the N1c wave or Tb) and verbal and non-verbal abilities in children with autism. The study was performed in 26 mentally retarded children with autism (AUT) aged 4-8 years (mean age +/- S.E.M. = 71 +/- 2 months; mean verbal and non-verbal developmental quotient +/- S.E.M. = 36 +/- 4 and 48 +/- 3). The stimuli used were 750 Hz tone bursts of 200 ms duration delivered binaurally at different intensity levels (50, 60, 70, 80 dB SPL) with 3-5 s interstimulus intervals. Temporal AEPs were first compared to those of a group of 16 normal children (NOR) in the same age range (mean age +/- S.E.M. = 69 +/- 3 months). We then focused on the AUT group and considered relations between temporal AEPs and the severity of disorders of verbal and non-verbal communication assessed using a behavior rating scale. AEPs recorded on left and right temporal sites were of smaller amplitude in the AUT group than in the NOR group. Increasing intensity-related amplitude was observed on both sides in NOR and only on the right side in AUT. The lack of intensity effect on the left side resulted in a particular pattern of asymmetry at the highest level of intensity (80 dB SPL) with greater N1c amplitude on the right than on the left side (the reverse was found in the NOR group). Electro-clinical correlations indicated that the greater the amplitude of the right temporal N1c responses, the higher the verbal and non-verbal communication abilities. This suggests a developmental reorganization of left-right hemisphere functions in autism, with preferential activation of the right hemisphere for functions usually allocated to the left hemisphere, particularly those involving the secondary auditory areas situated on the lateral surface of the superior temporal gyrus where the N1c/Tb wave is generated.

Topography of Syllable Change-Detection Electrophysiological Indices in Children and Adults with Reading Disabilities.

INTRODUCTION Developmental dyslexia (DD) is a frequent language-based learning disorder. The predominant etiological view postulates that reading problems originate from a phonological impairment. METHOD We studied mismatch negativity (MMN) and Late Discriminative Negativity (LDN) to syllables change in both children (n=12; 8-12 years) and young adults (n=15; 14-23 years) with DD compared with controls. RESULTS/DISCUSSION The present study confirmed abnormal automatic discrimination of syllable changes in both children and adults with developmental dyslexia. MMN topographic, amplitude and latency group differences were evidenced, suggesting different brain mechanisms involved in elementary auditory stimulus change-detection in DD, especially in the left hemisphere. The LDN results demonstrated that the auditory disorder of temporal processing in DD children becomes more serious at late stages of information processing and that the apparent cerebral hypo reactivity to speech changes in DD actually may correspond to additional processes. The age-related differences observed in both MMN and LDN topographies, amplitudes and latency between subjects with DD and controls could indicate different developmental courses in the neural representation of basic speech sounds in good and poor readers, with a tendency to normalization with increasing age. CONCLUSION Our results showing atypical electrophysiological concomitants of speech auditory perception in DD strongly support the hypothesis of deviant cortical organization in DD.

Frontal Evoked Responses, Stimulus Intensity Control, and the Extraversion Dimension

In her book, Individuality in Pain and Suffering, Petrie (1967) suggested wide differences among people in responsiveness to sensory stimulation. Three sets of individuals, called augmenters, moderates and reducers, with different tendencies were hypothesized based on their performances on a perceptual task, the kinesthetic figural after-effects (KFA) procedure. Augmenters judge the magnitude of a standard stimulus as larger after kinesthetic stimulation, moderates judge the standard as equal and reducers judge the standard as markedly reduced. These three types of individuals also differed in other psychophysiological and psychological characteristics such as tolerance for pain (Petrie et al., 1958) and the extraversion dimension (Petrie, 1967). The augmenting-reducing (Aug/Red) phenomenon was later investigated using neurophysiological measures of visual response (Buchsbaum and Pfefferbaum, 197 I ) , auditory response (Buchsbaum, 1974) and somatosensory response (Lavine e f al., 1976) to stimuli a t different intensities. It has been hypothesized that these patterns of responses might reflect a central nervous mechanism which controls stimulus intensity (Silverman et al., 1969). In other studies, the relationship between electrophysiological Aug/Red and other individual characteristics were examined; however, relationships with personality characteristics are still obscure. Petrie’s results on extraversion and Aug/Red (that reducers were more extraverted than augmenters) have not been reported with electrophysiological data. The purpose of the present work is to investigate whether individual differences in Aug/Red measured in the auditory modality are related to the extraversion dimension. We shall study Aug/Red both a t central and frontal sites. Reducing has been classically observed at the vertex lead (Buchsbaum and Pfefferbaum, 1971); the frontal lead will be considered since Petrie (1958) showed that surgery of the brain’s prefrontal areas modifies sensitivity to pain, satiability measures with KFA test, and extraversion.

An electrophysiological correlate of voice processing in 4- to 5-year-old children

Cortical auditory evoked potentials were studied in responses to voice and environmental sounds in 4- to 5-year-old children. A specific response to voice was dissociated from the response to environmental sounds. It appeared as a positive deflection recorded at right fronto-temporal sites and beginning within 60ms of stimulus onset. We termed this response Fronto-Temporal Positivity to Voice (FTPV).

Electrophysiological correlates of automatic visual change detection in school-age children

Automatic stimulus-change detection is usually investigated in the auditory modality by studying Mismatch Negativity (MMN). Although the change-detection process occurs in all sensory modalities, little is known about visual deviance detection, particularly regarding the development of this brain function throughout childhood. The aim of the present study was to examine the maturation of the electrophysiological response to unattended deviant visual stimuli in 11-year-old children. Twelve children and 12 adults were presented with a passive visual oddball paradigm using dynamic stimuli involving changes in form and motion. Visual Mismatch responses were identified over occipito-parietal sites in both groups but they displayed several differences. In adults the response clearly culminated at around 210 ms whereas in children three successive negative deflections were evidenced between 150 and 330 ms. Moreover, the main mismatch response in children was characterized by a positive component peaking over occipito-parieto-temporal regions around 450 ms after deviant stimulus onset. The findings showed that the organization of the vMMN response is not mature in 11-year-old children and that a longer time is still necessary to process simple visual deviancy at this late stage of child development.

Electrophysiological evidence of atypical visual change detection in adults with autism

Although atypical change detection processes have been highlighted in the auditory modality in autism spectrum disorder (ASD), little is known about these processes in the visual modality. The aim of the present study was therefore to investigate visual change detection in adults with ASD, taking into account the salience of change, in order to determine whether this ability is affected in this disorder. Thirteen adults with ASD and 13 controls were presented with a passive visual three stimuli oddball paradigm. The findings revealed atypical visual change processing in ASD. Whereas controls displayed a vMMN in response to deviant and a novelty P3 in response to novel stimuli, patients with ASD displayed a novelty P3 in response to both deviant and novel stimuli. These results thus suggested atypical orientation of attention toward unattended minor changes in ASD that might contribute to the intolerance of change.

Auditory evoked potentials to tones and syllables in adults: evidence of specific influence on N250 wave

Late auditory evoked potentials were recorded in eight adults according to stimulus duration (50ms versus 250ms) and to speech nature of the stimulus (tones versus syllables). The main effect of these parameters concerned the negative fronto-central wave, which occurs beyond 200ms termed N250 in this paper; it had a greater amplitude and a longer latency when tone duration increased from 50 to 250ms and a longer latency, a greater amplitude and a longer time-course in response to syllables compared to tones. Moreover, this wave was inversed in polarity at the mastoid sites, indicating the involvement of generators of the N250 wave in the supratemporal auditory cortex. These results showing the sensitivity of the N250 wave to tone duration and to speech stimuli indicated that this electrophysiological index might allow further assessment of cortical activity involved in speech stimuli processing.

Is my voice just a familiar voice? An electrophysiological study

It is not clear whether self-stimuli are processed by the brain as highly familiar overlearned stimuli or as self-specific stimuli. This study examined the neural processes underlying discrimination of ones own voice (OV) compared with a familiar voice (FV) using electrophysiological methods. Event-related potentials were recorded while healthy subjects (n = 15) listened passively to oddball sequences composed of recordings of the French vowel /a/ pronounced either by the participant her/himself, or by a familiar person or an unknown person. The results indicated that, although mismatch negativity displayed similar peak latency and amplitude in both conditions, the amplitude of the subsequent P3a was significantly smaller in response to OV compared with a FV. This study therefore indicated that fewer pre-attentional processes are involved in the discrimination of ones OV than in the discrimination of FVs.

Hallucinations and negative symptoms differentially revealed by frontal and temporal responses to speech in schizophrenia

BACKGROUND Auditory verbal hallucinations (AVH) in schizophrenia may arise because of aberrant speech perception. We used an electroencephalography method to examine the neural processes underlying speech perception in schizophrenic patients with hallucinations. METHODS Cortical event-related potentials (ERPs) were analyzed topographically (scalp potential and scalp current density (SCD) mapping) in response to the vowel /a/ using a passive paradigm in 26 patients with schizophrenia. RESULTS From the SCD distribution of the P1 peak, we showed that, whereas the hallucination score (PSYRATS) was negatively correlated with the amplitude of the frontal currents, the PANSS negative symptom score was negatively correlated with the amplitude of the temporal currents in patients with schizophrenia. CONCLUSIONS These results provide evidence that AVH and negative symptoms are associated with abnormal early processing of speech. Whereas AVH are related to decreased early frontal activation, negative symptoms are associated with a reduced early temporal response.