Development of visual evoked potentials and photic driving responses in normal full term, low risk premature, and Trisomy-21 infants during the first year of life

Somatosensory Cross-Modal Reorganization in Children With Cochlear Implants

Deprived of sensory input, as in deafness, the brain tends to reorganize. Cross-modal reorganization occurs when cortices associated with deficient sensory modalities are recruited by other, intact senses for processing of the latter's sensory input. Studies have shown that this type of reorganization may affect outcomes when sensory stimulation is later introduced via intervention devices. One such device is the cochlear implant (CI). Hundreds of thousands of CIs have been fitted on people with hearing impairment worldwide, many of them children. Factors such as age of implantation have proven useful in predicting speech perception outcome with these devices in children. However, a portion of the variance in speech understanding ability remains unexplained. It is possible that the degree of cross-modal reorganization may explain additional variability in listening outcomes. Thus, the current study aimed to examine possible somatosensory cross-modal reorganization of the auditory cortices. To this end we used high density EEG to record cortical responses to vibrotactile stimuli in children with normal hearing (NH) and those with CIs. We first investigated cortical somatosensory evoked potentials (CSEP) in NH children, in order to establish normal patterns of CSEP waveform morphology and sources of cortical activity. We then compared CSEP waveforms and estimations of cortical sources between NH children and those with CIs to assess the degree of somatosensory cross-modal reorganization. Results showed that NH children showed expected patterns of CSEP and current density reconstructions, such that postcentral cortices were activated contralaterally to the side of stimulation. Participants with CIs also showed this pattern of activity. However, in addition, they showed activation of auditory cortical areas in response to somatosensory stimulation. Additionally, certain CSEP waveform components were significantly earlier in the CI group than the children with NH. These results are taken as evidence of cross-modal reorganization by the somatosensory modality in children with CIs. Speech perception in noise scores were negatively associated with CSEP waveform components latencies in the CI group, suggesting that the degree of cross-modal reorganization is related to speech perception outcomes. These findings may have implications for clinical rehabilitation in children with cochlear implants.

Cortical evoked potentials in children of diabetic mothers

Type 1 diabetic mothers' infants show a delay of visual evoked potential (VEP) significantly related to some parameters of poor metabolic control during pregnancy. In the present paper we analyzed the characteristics of VEPs and somatosensory evoked potentials (SEPs) recorded in 16 three-year-old type 1 diabetic mothers' children (DMC). Compared with controls (23 nondiabetic mothers' healthy matched children), DMC showed significantly delayed mean latency of VEP (P2) and SEP (P22). In 3 cases (19%), we found pathological responses (+3 SD from the mean value of controls) of VEPs and SEPs. At the age of 3 years, the offspring of type 1 diabetic mothers showed delay of cortical evoked responses in both visual and somatosensory systems.

Flash visually evoked potentials in the newborn and their maturation during the first six months of life

The aim of this paper has been to obtain normative data for the major components of the visually evoked potentials obtained by flash stimulus (F-PEV) in the newborn, and to analyse the evolution of these responses during the first 24 weeks of life. In order to do so, F-VEP were recorded in 109 normal full-term newborn infants. Fifty-five of these infants were also studied longitudinally at 4, 8, 12 and 24 weeks. We recorded responses in all newborns. A great morphological variability was observed. P2 was the only component present in all of these infants. Early components, which were always present from the fourth week of life on, were recorded in 34% of the newborns. There were significant differences according to waking/sleep state. At 24 weeks the most characteristic response was a triphasic waveform with clear negative-positive-negative components at 67.9, 110 and 158.3 ms. The morphological variability observed in the F-PEV of the newborn and the presence of early components in some cases, suggest differences in the maturation of the specific and unspecific visual system at birth. The study of these responses provides us with information about certain aspects of visual maturation. The relative stability of P2 response of the newborn and of the early negative components later on, made them the most useful components to be used in paediatric clinical work . The latency of P2 in the newborn is the parameter that showed lower variability, and therefore the most suitable one to establish normative data.

Sensory evoked potentials in infants with Down syndrome

AIM

To investigate the sensory functions of the peripheral to central pathways in infants with Down syndrome (DS) by sensory evoked potentials.

METHODS

Fifty-five infants, 30 DS infants and 25 controls, were examined by multimodal evoked potentials, including brainstem auditory evoked potentials (BAEP), visual evoked potentials (VEP) and short-latency somatosensory evoked potentials (SSEP).

RESULTS

No obvious difference was found in the peak latencies between the two groups for BAEP. Nine children with DS showed abnormal BAEP; six had hearing loss and three had prolonged wave I latencies. For VEP, the peak latencies of P(2) and N(2) were significantly longer and the amplitudes were smaller in the DS group than in the control group. Of the 30 infants with DS, five had significantly prolonged P(2) latencies and two had lower amplitudes. In SSEP, the mean latencies of N(20) and the interpeak latencies of N(13)-N(20) of the infants with DS showed apparent prolongation compared to the controls. Seven of 30 (23.3%) DS patients had prolonged N(20) latencies.

CONCLUSION

Our results indicate that various sensory deficits occur in patients with DS during the first year of life.

Visual evoked potentials in disproportionately growth-retarded human neonates

To study brain function in the neonatal period, disproportionately growth-retarded (n = 33) and appropriately grown (n = 21) infants were examined using Doppler flow velocities prenatally and visual evoked potentials postnatally. Visual evoked potentials recordings were made at gestation of 40 and 46 weeks. The group of growth-retarded infants had significantly prolonged latencies to both of the two major peaks (designated P and N), most pronounced for the P peak. This result was observed at both ages investigated and corresponds to a developmental delay of 3 weeks. For individuals, the increase in P latency correlated to prenatal flow indices and to neonatal anthropometric parameters indicative of growth retardation. We conclude that in utero growth retardation affects brain development as assessed by visual evoked potentials in the neonatal period. This developmental delay may be produced by intracerebral factors during the process of growth retardation, and these alterations may have a prognostic value.

Cortical visual evoked potentials in very low birthweight premature infants

OBJECTIVES

To compare the age of onset of the pattern orientation reversal visual evoked potential (OR-VEP) in a group of very low birthweight (VLBW) premature infants with term infants matched for postconceptual age at testing. The OR-VEP measure is used as an indicator of visual cortical functioning because of the specificity of cortical neurones in showing sensitivity to changes of slant or orientation.

DESIGN

Results are given for 24 VLBW infants, born at 24-32 weeks gestation weighing less than 1500 g, and 31 infants born at term. The steady state evoked potential to a grating pattern reversing in orientation (between 45 degrees and 135 degrees) at 4 reversals/second and 8 reversals/second was recorded.

RESULTS

The VLBW infants with normal neonatal ultrasound results (and normal neurological outcome at 3 years of age) showed a significant OR-VEP with a similar postnatal time course to the term infants. Four premature infants, showing appreciable abnormalities on ultrasound examination, did not show normal onset of the OR-VEP, and all had an abnormal neurological outcome.

CONCLUSIONS

This result can be taken to indicate that the onset of cortical function is similar in healthy preterm infants to term infants. The visual development of the premature infants was neither accelerated nor delayed as a result of their extra visual experience. The OR-VEP can be used as a prognostic indicator of early brain development alongside other neurological measures. It may also be a very early indicator of later neurological outcome.

Effects of prenatal substance exposure: altered maturation of visual evoked potentials

We investigated the effects of prenatal substance use on visual evoked potentials (VEPs). Seventy-four children were tested at birth and 1 month of age with binocular flash VEPs and at 4, 8, and 18 months of age with binocular pattern VEPs. Regressions were run by trimester to assess the independent effects of substance exposure. Variables included in the regression model were alcohol, marijuana, tobacco, other drug use for each trimester, maternal age, education, income, race, marital status, infant sex, birthweight, and Dubowitz score. Changes in specific components of the binocular VEP were both substance- and trimester-specific. First trimester alcohol use was associated with prolonged P1 wave latencies at 1 month of age. Prolonged P1 wave latencies at birth and 18 months were associated with tobacco use during each of the three trimesters, at 1 and 18 months with third trimester marijuana use, and at 1 and 18 months with first trimester other illicit drug use. Although these women were moderate substance users during pregnancy, their offspring exhibited maturational changes in components of the VEP in the absence of neonatal behavioral disturbances.

Prognostic value of visual evoked potentials (VEP) in infants with visual inattentiveness

Visual evoked potentials elicited by strobe flash (fVEPs) were recorded in 56 infants (3 months to 15 months of age) with visual inattentiveness but without prechiasmal problems. Their visual status was reexamined one or more years later when 41 children were found to be visually competent (Group NB) and 15 were blind (Group B). We also evaluated a group of 32 age-matched children who had no visual symptoms (Group C). It was found that well organized VEP waveforms over one or both hemispheres (Types U and S), or those with a characteristic negative shift (Type N) suggest favorable prognosis. Integrated voltage of the VEP correlated well with long-term prognosis for visual recovery. The vertex VEP also (had) provided some predictions for visual prognosis. Overall results indicate good prognosis if related to sufficient voltage and complexity of the VEP components.

Effects of bilirubin on visual evoked potentials in term infants

To determine bilirubin-induced neurotoxicity, serial visual evoked potentials (VEPs) of 72 infants with neonatal hyperbilirubinaemia and 22 controls were evaluated and compared in four sessions for 8 weeks after birth. The levels of maximal serum bilirubin were found positively related to the wave latencies of first VEP. Within 8 weeks after birth, the wave latencies were significantly prolonged in infants in the severe and moderate groups than in the controls. The amplitudes of VEPs were apparently lower in severe and moderate groups than in the control group only in the 1st week after birth. At 1 year, 4 of the 18 infants in the severe group had poor motor skills and one had general hypotonia.

CONCLUSION

These results suggest that bilirubin may affect the visual pathways, and that VEP is a useful adjunct to the neurological assessment of neonatal hyperbilirubinaemia.

Cerebral blood flow and EEG changes in preterm infants with patent ductus arteriosus

It is unknown whether the decreased cerebral blood flow seen in infants with a large patent ductus arteriosus is associated with cerebral dysfunction. Decreased cerebral blood flow in adult human and animal models has been associated with altered electroencephalography (EEG), spectral-analyzed EEG, and EEG response to photic stimulation. Cerebral blood flow velocity, EEG, spectral analysis of EEG, and photic alteration of EEG spectra were evaluated in 8 infants before and after closure of a significant patent ductus arteriosus and in 10 control infants without a patent ductus arteriosus. All infants with patent ductus arteriosus had moderate or large shunts associated with a 25% mean reduction in cerebral blood flow velocity. There were no differences, however, in EEG, spectral analysis of EEG, or photic alteration of the spectral analysis for these infants before and after patent ductus arteriosus closure as compared to controls. It is concluded that the degree of decreased cerebral blood flow in infants with a significant patent ductus arteriosus is not sufficient to cause measurable alteration in electrocortical activity.

The dynamics of phase relationships of alpha waves during photic driving

Inter- and intrahemispheric phase relationships of alpha waves during photic driving with intermittent flash stimuli were successively calculated by our newly developed method and compared with the results obtained during the resting condition. Of 12 healthy subjects, 6 showed obvious photic driving responses in the occipital regions (driven group) but the remaining 6 did not (non-driven group). In the driven group, the interhemispheric phase differences decreased, especially when EEG frequencies coincided with stimulating frequencies. However, this was not maintained throughout the stimulation period but was accompanied by some fluctuation. The interhemispheric phase difference decreased in the posterior temporal and, in particular, in the occipital areas. The intrahemispheric phase difference for the occipito-frontal and the occipito-central pairs in each hemisphere tended to increase and remained at approximately pi radians, especially for the former pair. These findings suggest the presence of a specific response in the occipital area. Time ratios of the phase lead in longitudinal and transverse directions and the high similarity of the time courses of intrahemispheric phase differences between bilaterally homologous pairs at rest suggest that there exist phasing mechanisms which act in parallel between the left and right hemispheres with dominant antero-posterior time delay.

Pattern-reversal visual evoked potentials in Down's syndrome

We examined pattern-reversal visual evoked potentials (PRVEPs) in 36 adult patients with Down's syndrome, and analyzed the effects of the ophthalmological abnormalities on results of PRVEPs. The P100 latency was significantly delayed in 24 eyes of 16 patients. The P100 latency was significantly longer and its amplitude was significantly smaller (P < 0.001) in Down's syndrome patients than in age-matched normal controls. In 9 patients without any ophthalmological abnormalities, P100 latency showed no significant difference from that in normal controls, but three of them showed a significant delay of P100. Their P100 amplitudes were significantly smaller than those in normal controls. Therefore, we considered that the ophthalmological abnormalities are one of the main factors causing PRVEPs abnormalities in Down's syndrome patients, but some unknown factors should be also responsible.

Heart-rate variability in low-risk prematurely born infants reaching normal term: a comparison with full-term newborns

To investigate the influence of prematurity and postnatal age on the maturation of the autonomic nervous system function, we analysed heart-rate and heart-rate variability in twelve prematurely born infants (< 37 weeks gestational age) reaching the conceptional age of 37-41 weeks. These neonates were compared with sixteen 37-41 week conceptional age newborns (< 10 days postnatal age). Heart-rate variability was analysed by spectral analysis of interbeat intervals using Short-Time Fourier Transform. We found that during both active and quiet sleep, the durations of RR-intervals were shorter and the amplitude of heart-rate variability in different frequency bands was lower in prematures reaching term than in newborns of the same conceptional age (P < 0.001). Between-state comparison showed differences in both groups. In both groups, low-frequency heart-rate variability was higher in active sleep than in quiet sleep. Between-state differences of RR-intervals and high-frequency heart-rate variability were present only in newborns (P < 0.01). Discrimination between newborns and prematures reaching term, based on RR-intervals and heart-rate variability, was correct in both sleep states with errors between 7 to 16%. However, in both newborns and prematures reaching term, between-state discrimination showed less reliable results, especially for quiet sleep discrimination with 24% (in PRT) and 20% (in NB) of errors. Our results, especially information given by factor analysis, suggest that the differences between newborns and prematures reaching term, concerning RR-interval and heart-rate variability, may be related to a changed balance between the sympathetic and parasympathetic nervous systems with a diminished parasympathetic component of heart rate control in prematures reaching term, as compared to newborns.

The development of auditory and visual evoked potentials in early treated phenylketonuric children

Brain-stem auditory evoked potentials (BAEPs) and flash visual evoked potentials (F-VEPs) were gathered from 8 early treated phenylketonuric (PKU) children in a prospective longitudinal investigation during the 1st to the 12th months after birth. No consistent differences were found in the wave morphology of evoked potentials in PKU children from that of age-matched controls. Studying the latency of some components showed that in BAEPs, wave I latency was similar to control values for the whole year, but that the I-V interpeak mean latency (I-V IPL) was always significantly longer than in controls. In F-VEPs wave N1 latency was significantly longer than in controls only at 1-2 months of age, but returned to control values at 3-4 months (when all children were on dietary therapy) and remained in this range up to the 12th month. The mean latency of the P2 wave of flash VEPs was always significantly longer in PKU children than in controls. These results show that relevant alterations in evoked potentials may be found in PKU children several months after starting dietary therapy. This suggests that information processing in the brain may be impaired for a long time, due to abnormal metabolic conditions between birth and the onset of dietary therapy.

The effect of electrode position on flash visual evoked potentials in the newborn

We examined how changes in electrode position affected the visual evoked potential in 74 high-risk newborns using a multiple electrode technique. The variation in the visual evoked potential across the occiput was documented. Visual evoked potentials that were visible at one occipital electrode position were absent at a different electrode position in 21 of 87 recordings (24%). Changes of greater than 20 msec between electrodes in latency of waves P1 or N2 occurred in 34% and 29% of recordings, respectively. The amplitude of response varied by a factor of 2.36 between mid occipital and lateral occipital electrodes. The results demonstrated that large changes in morphologic characteristics, latency, and amplitude in the visual evoked potential of the newborn result from small changes in the position of recording electrodes. These findings underscored the importance of electrode position and accurate electrode placement. Our observations also indicated that recordings from a single electrode are inadequate in providing an accurate representation of the neonatal visual evoked potential.

Early development of brainstem auditory evoked potentials in Down's syndrome

Early development of brainstem auditory pathway was studied in 14 children with Down's syndrome (age range from 1 month to 3 years). The brainstem auditory evoked potentials (BAEP) during infancy was characterized by elevated threshold and poorly differentiated wave I. All children within 2 years had elevated threshold in one or both ears, suggesting a high incidence of peripheral hearing deficits. Follow-up tests showed that as age increased up to 3 years the elevated threshold gradually decreased and the differentiation of wave I improved. The I-V interpeak interval was slightly shorter and the amplitude of wave V was smaller than the normal controls, which existed continuously during follow-up studies. Our findings suggest that the development of peripheral hearing is delayed, although persistent hearing deficits cannot be excluded, and the functioning and development of the brainstem auditory pathway may also be abnormal in Down's syndrome children.

Electrophysiologic testing techniques for children

This practical article for clinical electrophysiologists discusses the evaluation of infant and child patients' visual systems using electroretinographic (ERG), electrooculographic (EOG), and visually evoked potential (VEP) techniques. These techniques not only help to secure specific diagnoses, but by systematic assessment of function along the visual pathways can also localize dysfunction underlying visual deficits of pediatric patients. Among children, development as well as disease can affect electrophysiological parameters. Therefore diagnosis of normal or abnormal depends critically on an adequate description of normal responses for age. Procedures that the authors have found feasible, reliable, and valid are summarized. Standardization of pediatric testing appears to be an important next step. The power of ERG, EOG and VEP recordings to demonstrate the neurophysiological basis for pediatric visual impairment is predicted to stimulate further research in this area.

Maturation of the neonatal somatosensory evoked response in preterm infants

A group of 102 neurologically normal neonates with gestations between 26 and 40 weeks, without abnormality on cranial ultrasound, underwent evoked response testing. Satisfactory results were obtained for 90 per cent of the infants. Normal ranges with 95 per cent tolerance limits for the short-latency N1 component of the response were obtained at postmenstrual ages between 29 weeks and term. Somatosensory evoked responses are a practical tool for evaluating sensorimotor pathways in the newborn infant's brain.