A topographical ERP study of healthy premature 5-year-old children in the auditory and visual modalities

Longstanding Auditory Sensory and Semantic Differences in Preterm Born Children

More than 10% of births are preterm, and the long-term consequences on sensory and semantic processing of non-linguistic information remain poorly understood. 17 very preterm-born children (born at < 33 weeks gestational age) and 15 full-term controls were tested at 10 years old with an auditory object recognition task, while 64-channel auditory evoked potentials (AEPs) were recorded. Sounds consisted of living (animal and human vocalizations) and manmade objects (e.g. household objects, instruments, and tools). Despite similar recognition behavior, AEPs strikingly differed between full-term and preterm children. Starting at 50ms post-stimulus onset, AEPs from preterm children differed topographically from their full-term counterparts. Over the 108-224ms post-stimulus period, full-term children showed stronger AEPs in response to living objects, whereas preterm born children showed the reverse pattern; i.e. stronger AEPs in response to manmade objects. Differential brain activity between semantic categories could reliably classify children according to their preterm status. Moreover, this opposing pattern of differential responses to semantic categories of sounds was also observed in source estimations within a network of occipital, temporal and frontal regions. This study highlights how early life experience in terms of preterm birth shapes sensory and object processing later on in life.

Impact of prematurity on neurodevelopment

The consequences of prematurity on brain functional development are numerous and diverse, and impact all brain functions at different levels. Prematurity occurs between 22 and 36 weeks of gestation. This period is marked by extreme dynamics in the physiologic maturation, structural, and functional processes. These different processes appear sequentially or simultaneously. They are dependent on genetic and/or environmental factors. Disturbance of these processes or of the fine-tuning between them, when caring for premature children, is likely to induce disturbances in the structural and functional development of the immature neural networks. These will appear as impairments in learning skills progress and are likely to have a lasting impact on the development of children born prematurely. The level of severity depends on the initial alteration, whether structural or functional. In this chapter, after having briefly reviewed the neurodevelopmental, structural, and functional processes, we describe, in a nonexhaustive manner, the impact of prematurity on the different brain, motor, sensory, and cognitive functions.

Anodal Transcranial Direct Current Stimulation Promotes Frontal Compensatory Mechanisms in Healthy Elderly Subjects

Recent studies have demonstrated that transcranial direct current stimulation (tDCS) is potentially useful to improve working memory. In the present study, young and elderly subjects performed a working memory task (n-back task) during an electroencephalogram recording before and after receiving anodal, cathodal, and sham tDCS over the left dorsolateral prefrontal cortex (DLPFC). We investigated modulations of behavioral performance and electrophysiological correlates of working memory processes (frontal and parietal P300 event-related potentials). A strong tendency to modulated working memory performance was observed after the application of tDCS. In detail, young, but not elderly, subjects benefited from additional practice in the absence of real tDCS, as indicated by their more accurate responses after sham tDCS. The cathodal tDCS had no effect in any group of participants. Importantly, anodal tDCS improved accuracy in elderly. Moreover, increased accuracy after anodal tDCS was correlated with a larger frontal P300 amplitude. These findings suggest that, in elderly subjects, improved working memory after anodal tDCS applied over the left DLPFC may be related to the promotion of frontal compensatory mechanisms, which are related to attentional processes.

Less Efficient Neural Processing Related to Irregular Sleep and Less Sustained Attention in Toddlers

The current study used event-related potentials to examine a candidate process through which sleep difficulties affect attentional processing in toddlers. Fifteen toddlers participated in an auditory Oddball task while neurophysiological data were collected. Sleep deficits were assessed using actigraphs, and attention was examined with a sustained attention task. A P3-like component was elicited from the toddlers, and longer target P3 latencies were associated with poorer sustained attention and irregular sleep. Findings suggest that irregular sleep is associated with less efficient attentional processing as reflected by the P3 component, and that longer target P3 latencies are associated with poorer sustained attention.

The development of visual P3a and P3b

The relationship of visual P3a and P3b to age and neuropsychological performance was investigated in 26 healthy children (6.8-15.8 years) and 129 adult volunteers (20.0-88.8 years). Within the sample of children, an effect of age on midline topography was observed, with higher frontal amplitudes in the youngest compared to the oldest children. Increasing age was associated with lower P3a and P3b amplitude and shorter P3b latency at Fz. Performance on neuropsychological tests (matrix reasoning from WASI, digit span from WAIS, word order and hand movement from Kaufman) was only weakly associated with measures of P3a and P3b. The analyses were then repeated with the full life-span sample (n = 155). It was found that for P3a, amplitude decreased and latency increased with age. For P3b, the pattern was more complex, with a nonlinear amplitude reduction and no latency change with age. It appears that the development of P3a in children represents the start of processes that later continue in the adult life-span, but that the automatic processes indexed by P3a seems to mature earlier than the controlled processes reflected by P3b. Finally, it was demonstrated that the relationships between neuropsychological test scores (matrix reasoning, digit span) and P3 parameters were complex, following a mix of linear and nonlinear patterns. It is suggested that the neuropsychological significance of the different P3a and P3b parameters may change from childhood to the adult life-span.

Left temporal impairment of auditory information processing in prematurely born 9-year-old children: An electrophysiological study

Children born preterm more than average display cognitive difficulties that are significant enough to prevent normal schooling. The aim of our study was to provide better understanding of the long-term neuropathological processes associated with preterm injury, through the hypothesis that mild cognitive disorders might be related to slight deficits in primary functions such as attention and perception. Assessment of auditory pre-attentive processes was performed by recording the obligatory sensory response (N250) and the change-detection response (Mismatch Negativity, MMN). Topographic study of these responses was performed in fifteen 9-year-old children born preterm (27-33 weeks gestational age) matched to fifteen control children born at term. The auditory stimulus sequence consisted of 1000 Hz standard and 1100 Hz deviant tones (15%) delivered binaurally with an interstimulus interval of 700 ms. The results showed that MMN was similar in both groups. Analysis of the responses to standard repetitive tones demonstrated significantly smaller N250 wave amplitude in children born preterm. Scalp current density maps showed that this reduction in amplitude was associated with lower activity of both frontal and left supratemporal generators. Although the functional significance of the N250 wave in children remains to be clarified, our results indicate a disorder of auditory processes related to prematurity that might have consequences on the development of higher-level processes.

Maturation of the cortical auditory evoked potential in infants and young children

The aim of this study was to evaluate the maturation of the cortical auditory evoked potential (CAEP) in humans. The participants in this experiment were 10 newborns (<7 days), 19 toddlers (13-41 months), 20 children (4-6 years) and 9 adults (18-45 years). CAEPs were obtained in response to low (400 Hz) and high (3000 Hz) tones and to the word token /baed/, all presented at 60 dB HL, at a rate of 0.22 Hz. Latency and amplitude measures were made for CAEP components P1, N1, P2 and N2 as a function of participant age, stimulus type and electrode montage. CAEP component latencies were relatively stable from birth to 6 years, but adults demonstrated significantly shorter latencies compared to infants and children. Components P1 and N2 decreased in amplitude, while components N1 and P2 increased in amplitude from birth to adulthood. Words evoked significantly larger CAEPs in newborns compared to responses evoked by tones, but in other age groups the effects of stimulus type on component amplitudes and latencies were less consistent. There was evidence of immature tonotopic organisation of the generators of N1 when responses from infants and young children were compared to those of adults. The scalp distribution of components N1 and P2 was clearly different in newborns and toddlers compared to children and adults. In the younger groups, both N1 and P2 were uniformly distributed across the scalp but in children and adults these components showed more focal distributions, with evidence of response laterality increasing with maturity. The results of the present study describe, for the first time, CAEPs recorded from multiple scalp electrodes, for tones and speech stimuli, in infants and children from birth to 6 years of age. Frequency-related differences in component amplitude were apparent at all ages reflecting development of tonotopic organisation of the CAEP neural generators.

Maturation of CAEP in infants and children: A review

This paper reviews our current understanding of the development of the obligatory cortical auditory evoked potential (CAEP) components P1, N1, P2, and N2. Firstly, the adult CAEP is briefly reviewed with respect to its morphology, neural generators and stimulus-dependence. Secondly, age-related changes occurring from the newborn period through childhood and adolescence are reviewed. The focus is on the maturation of CAEP morphology, changes in the scalp topography of the various components, changes in their amplitude and latency and in their stimulus-dependence. This review identifies periods of development in which we have only limited understanding of cortical auditory processing, as revealed by evoked potentials.

Meta-analysis of P300 and schizophrenia: patients, paradigms, and practical implications

The goal of the present meta-analysis was to identify factors that contribute to P300 event-related brain potential (ERP) differences in patients with schizophrenia compared to unaffected controls in an attempt to characterize the clinically relevant dimensions underlying P300 deficits in patients with schizophrenia. P300 effect size (d) was smaller in amplitude and longer in latency in schizophrenic patients compared to normal controls, with the strongest effects obtained from the auditory oddball. Paranoid subtype demonstrated larger P300 amplitude effect sizes than other disease subtypes, and P300 latency effect size decreased with disease duration. Psychopathology severity and antipsychotic medications were unrelated to P300 amplitude effect size. Gender proportion, educational level, and stimulus and task variables also affected P300 amplitude and latency effect sizes. The findings are used to formulate a theoretical account of the empirical data and provide suggestions for maximizing the utility of the P300 component in the assessment of schizophrenia.

Event related potentials during attention tasks in VLBW children with and without attention deficit disorder

OBJECTIVE

Children born prematurely have a higher incidence of attention deficit disorder with or without hyperactivity. We have used visual event related potentials to study possible brain dysfunctions that could explain this higher incidence.

METHODS

Very low birth weight (VLBW) children with and without AD/HD and term born children with and without AD/HD, were matched for IQ, age and socio-economic status (n=41, mean age 104 months). A visual oddball paradigm, consisting of target and non-target stimuli, was used with analysis of response times, error scores, N200, P300 and a P500 component.

RESULTS

AD/HD children responded slower (F (1,38)=11.20, p<0.002); more varied (F (1,38)=21.77, p<0.000) and made more commission and omission errors (Kruskal-Wallis p<0.000). Non-target N200 was increased in amplitude (F (1.39)=4.01, p=0.05) with a wide anterior topography in children with AD/HD. The late positivity (P500) was decreased over central leads in children with AD/HD during the non-target stimuli (F (3,75)=3.00, p<0.036). No differences could be found in latency, amplitude or topography between VLBW children with AD/HD and term born children with AD/HD.

CONCLUSIONS

Prematurity does not induce specific attentional brain dysfunction or maturation delays in stimulus processing during cognitive tasks. Other factors should be investigated to explain the higher incidence of AD/HD in VLBW children.

Effects of stimulus frequency and complexity on the mismatch negativity and other components of the cortical auditory-evoked potential

This study investigated, first, the effect of stimulus frequency on mismatch negativity (MMN), N1, and P2 components of the cortical auditory event-related potential (ERP) evoked during passive listening to an oddball sequence. The hypothesis was that these components would show frequency-related changes, reflected in their latency and magnitude. Second, the effect of stimulus complexity on those same ERPs was investigated using words and consonant-vowel tokens (CVs) discriminated on the basis of formant change. Twelve normally hearing listeners were tested with tone bursts in the speech frequency range (400/440, 1,500/1,650, and 3,000/3,300 Hz), words (/baed/ vs /daed/) and CVs (/bae/ vs /dae/). N1 amplitude and latency decreased as frequency increased. P2 amplitude, but not latency, decreased as frequency increased. Frequency-related changes in MMN were similar to those for N1, resulting in a larger MMN area to low frequency contrasts. N1 amplitude and latency for speech sounds were similar to those found for low tones but MMN had a smaller area. Overall, MMN was present in 46%-71% of tests for tone contrasts but for only 25%-32% of speech contrasts. The magnitude of N1 and MMN for tones appear to be closely related, and both reflect the tonotopicity of the auditory cortex.

P300 as a measure of cognitive dysfunction from occupational and environmental insults

The P300 component of the event-related brain potential (ERP) is a sensitive, non-invasive, and convenient measure of cognitive dysfunction resulting from a variety of etiological agents. Application-orientated research on using the P300 measure as a cognitive probe for a wide range of neurological and psychiatric situations has been expanding rapidly in the last decade.The aim of this paper is to preview issues of application-oriented P300 research in occupational and environment medicine. Firstly, the neurophysiological background of the P300 is outlined. Secondly, the recent findings of P300 abnormalities following various occupational and environmental exposures are overviewed. Thirdly, the empirical issues for application-oriented research such as the potential causes of variability, limitation and difficulty are summarized, with suggestion for controlling them and for future standardization. Finally, it is concluded that P300 assessments demonstrate promising possibility as a sensitive marker for general cognitive dysfunction in occupational and environmental medicine.

P300 habituation patterns: individual differences from ultradian rhythms

Event-related brain potentials (ERPs) were elicited with auditory stimuli from normal subjects every 10 min. for 10 successive trial blocks to assess ultradian influences on the P300 component. Based on a theoretical analysis of the underlying relationship between background EEG activity and P300 variability, subjects were divided into two groups according to whether P300 amplitude increased or decreased initially over trial blocks. P300 amplitude habituated across trial blocks. P300 latency produced systematic cyclical variation with approximately a 90-min. period that was opposite in phase for the different subject groups. The findings suggest that ultradian rhythms contribute to P300 latency variability. The implications of the results for P300 in applied settings are discussed.

Age effects on central nervous system activity reflected in the olfactory event-related potential. Evidence for decline in middle age

A series of studies in this laboratory using the olfactory event-related potential (OERP) have examined the underlying central nervous system activity associated with age-related changes in olfactory functioning. Early (sensory) components of the OERP showed reduced amplitude and longer latency in elderly subjects, with larger effects in males. Amplitudes are already decreased in middle age. The late cognitive component, P3, showed a longer latency as well as a decreased amplitude in the elderly, with effect sizes for age significantly larger for the late component than for the early components. We report here the significantly longer latency, particularly for the P3, in middle-aged persons, suggesting age-related slowing of olfactory information processing as early as the 50s. Results suggest that the elderly brain, and indeed, the middle-aged brain shows smaller responses to odors, is less able to allocate attentional resources and slows in its olfactory cognitive processing. The OERP is a potent reflection of these changes.