Neonatal somatosensory evoked potentials persist during hypothermia

AIM

Treatment with therapeutic hypothermia has challenged the use of amplitude-integrated electroencephalography in predicting outcomes after perinatal asphyxia. In this study, we assessed the feasibility and gain of somatosensory evoked potentials (SEP) during hypothermia.

METHODS

This retrospective study comprised neonates from 35 + 6 to 42 + 2 gestational weeks and treated for asphyxia or hypoxic-ischaemic encephalopathy at Helsinki University Hospital between 14 February 2007 and 23 December 2009. This period was partly before the introduction of routine therapeutic hypothermia, which enabled us to include normothermic neonates who would these days receive hypothermia treatment. We analysed SEPs from 47 asphyxiated neonates and compared the results between 23 normothermic and 24 hypothermic neonates.

RESULTS

Our data showed that hypothermia led to SEP latencies lengthening by a few milliseconds, but the essential gain for predicting outcomes by SEPs was preserved during hypothermia. Of the 24 hypothermic neonates, bilaterally absent SEPs were associated with poor outcome in 2/2 neonates, normal SEPs were associated with good outcomes in 13/15 neonates and 5/7 neonates with unilaterally absent or grossly delayed SEPs had a poor outcome.

CONCLUSION

Our findings indicated that SEPs were a reliable tool for evaluating the somatosensory system in asphyxiated neonates in both normothermic and hypothermic conditions.

Evoked potentials recorded during routine EEG predict outcome after perinatal asphyxia

OBJECTIVE

To evaluate the added value of somatosensory (SEPs) and visual evoked potentials (VEPs) recorded simultaneously with routine EEG in early outcome prediction of newborns with hypoxic-ischemic encephalopathy under modern intensive care.

METHODS

We simultaneously recorded multichannel EEG, median nerve SEPs, and flash VEPs during the first few postnatal days in 50 term newborns with hypoxic-ischemic encephalopathy. EEG background was scored into five grades and the worst two grades were considered to indicate poor cerebral recovery. Evoked potentials were classified as absent or present. Clinical outcome was determined from the medical records at a median age of 21months. Unfavorable outcome included cerebral palsy, severe mental retardation, severe epilepsy, or death.

RESULTS

The accuracy of outcome prediction was 98% with SEPs compared to 90% with EEG. EEG alone always predicted unfavorable outcome when it was inactive (n=9), and favorable outcome when it was normal or only mildly abnormal (n=17). However, newborns with moderate or severe EEG background abnormality could have either favorable or unfavorable outcome, which was correctly predicted by SEP in all but one newborn (accuracy in this subgroup 96%). Absent VEPs were always associated with an inactive EEG, and an unfavorable outcome. However, presence of VEPs did not guarantee a favorable outcome.

CONCLUSIONS

SEPs accurately predict clinical outcomes in newborns with hypoxic-ischemic encephalopathy and improve the EEG-based prediction particularly in those newborns with severely or moderately abnormal EEG findings.

SIGNIFICANCE

SEPs should be added to routine EEG recordings for early bedside assessment of newborns with hypoxic-ischemic encephalopathy.

Lack of Cortical Correlates of Response Inhibition in 6-Year-Olds Born Extremely Preterm - Evidence from a Go/NoGo Task in Magnetoencephalographic Recordings

Children born extremely preterm (EPT) may have difficulties in response inhibition, but the neural basis of such problems is unknown. We recorded magnetoencephalography (MEG) during a somatosensory Go/NoGo task in 6-year-old children born EPT (n = 22) and in children born full term (FT; n = 21). The children received tactile stimuli randomly to their left little (target) and index (non-target) finger and were instructed to squeeze a soft toy with the opposite hand every time they felt a stimulus on the little finger. Behaviorally, the EPT children performed worse than the FT children, both in responding to the target finger stimulation and in refraining from responding to the non-target finger stimulation. In MEG, after the non-target finger stimulation (i.e., during the response inhibition), the sensorimotor alpha oscillation levels in the contralateral-to-squeeze hemisphere were elevated in the FT children when compared with a condition with corresponding stimulation but no task (instead the children were listening to a story and not attending to the fingers). This NoGo task effect was absent in the EPT children. Further, in the sensorimotor cortex contralateral to the tactile stimulation, the post-stimulus suppression was less pronounced in the EPT than FT children. We suggest that the missing NoGo task effect and lower suppression of sensorimotor oscillations are markers of deficient functioning of the sensorimotor networks in the EPT children.

Peripheral neuropathy in patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency - A follow-up EMG study of 12 patients

BACKGROUND

The neonatal screening and early start of the dietary therapy have improved the outcome of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). The acute symptoms of LCHADD are hypoketotic hypoglycemia, failure to thrive, hepatopathy and rhabdomyolysis. Long term complications are retinopathy and neuropathy. Speculated etiology of these long term complications are the accumulation and toxicity of hydroxylacylcarnitines and long-chain fatty acid metabolites or deficiency of essential fatty acids.

AIMS

To study the possible development of polyneuropathy in LCHADD patients with current dietary regimen.

METHODS

Development of polyneuropathy in 12 LCHADD patients with the homozygous common mutation c.G1528C was evaluated with electroneurography (ENG) studies. The ENG was done 1-12 times to each patient, between the ages of 3 and 40 years. Clinical data of the patients were collected from the patient records.

RESULTS

The first sign of polyneuropathy was detected between the ages of 6-12 years, the first abnormality being reduction of the sensory amplitudes of the sural nerves. With time, progression was detected by abnormalities in sensory responses extending to upper limbs, as well as abnormalities in motor responses in lower limbs. Altogether, eight of the patients had polyneuropathy, despite good compliancy of the diet.

CONCLUSIONS

This study is the first to report the evolution of polyneuropathy with clinical neurophysiological methods in a relative large LCHADD patient group. Despite early start, and good compliance of the therapy, 6/10 of the younger patients developed neuropathy. However, in most patients the polyneuropathy was less severe than previously described.

Somatosensory and auditory processing in opioid-exposed newborns with neonatal abstinence syndrome: a magnetoencephalographic approach

OBJECTIVE

Opioid exposure during pregnancy is a potential risk factor for the developing central nervous system of the fetus. We studied evoked responses in buprenorphine-exposed newborns who displayed neonatal abstinence syndrome (NAS) to elucidate the possible alterations in functioning of the somatosensory and auditory systems.

METHODS

We compared somatosensory (SEFs) and auditory evoked magnetic fields (AEFs), recorded with magnetoencephalography (MEG), of 11 prenatally buprenorphine-exposed newborns with those of 12 healthy newborns. Peak latencies, source strength and location of SEFs or AEFs were recorded.

RESULTS

AEFs were present in all buprenorphine-exposed newborns without significant differences from those of healthy newborns. In contrast, though no group level differences in SEFs existed, at individual level the response deviated from the typical neonatal morphology in four buprenorphine-exposed newborns.

CONCLUSIONS

Although buprenorphine exposure during pregnancy does not seem to cause constant deficiencies in somatosensory or auditory processing, in some newborns the typical development of somatosensory networks may be - at least transiently - disrupted.

Development of Human Somatosensory Cortical Functions - What have We Learned from Magnetoencephalography: A Review

The mysteries of early development of cortical processing in humans have started to unravel with the help of new non-invasive brain research tools like multichannel magnetoencephalography (MEG). In this review, we evaluate, within a wider neuroscientific and clinical context, the value of MEG in studying normal and disturbed functional development of the human somatosensory system. The combination of excellent temporal resolution and good localization accuracy provided by MEG has, in the case of somatosensory studies, enabled the differentiation of activation patterns from the newborn’s primary (SI) and secondary somatosensory (SII) areas. Furthermore, MEG has shown that the functioning of both SI and SII in newborns has particular immature features in comparison with adults. In extremely preterm infants, the neonatal MEG response from SII also seems to potentially predict developmental outcome: those lacking SII responses at term show worse motor performance at age 2 years than those with normal SII responses at term. In older children with unilateral early brain lesions, bilateral alterations in somatosensory cortical activation detected in MEG imply that the impact of a localized insult may have an unexpectedly wide effect on cortical somatosensory networks. The achievements over the last decade show that MEG provides a unique approach for studying the development of the somatosensory system and its disturbances in childhood. MEG well complements other neuroimaging methods in studies of cortical processes in the developing brain.

Reactivity of sensorimotor oscillations is altered in children with hemiplegic cerebral palsy: A magnetoencephalographic study

Cerebral palsy (CP) is characterized by difficulty in control of movement and posture due to brain damage during early development. In addition, tactile discrimination deficits are prevalent in CP. To study the function of somatosensory and motor systems in CP, we compared the reactivity of sensorimotor cortical oscillations to median nerve stimulation in 12 hemiplegic CP children vs. 12 typically developing children using magnetoencephalography. We also determined the primary cortical somatosensory and motor representation areas of the affected hand in the CP children using somatosensory-evoked magnetic fields and navigated transcranial magnetic stimulation, respectively. We hypothesized that the reactivity of the sensorimotor oscillations in alpha (10 Hz) and beta (20 Hz) bands would be altered in CP and that the beta-band reactivity would depend on the individual pattern of motor representation. Accordingly, in children with CP, suppression and rebound of both oscillations after stimulation of the contralateral hand were smaller in the lesioned than intact hemisphere. Furthermore, in two of the three children with CP having ipsilateral motor representation, the beta- but not alpha-band modulations were absent in both hemispheres after affected hand stimulation suggesting abnormal sensorimotor network interactions in these individuals. The results are consistent with widespread alterations in information processing in the sensorimotor system and complement current understanding of sensorimotor network development after early brain insults. Precise knowledge of the functional sensorimotor network organization may be useful in tailoring individual rehabilitation for people with CP.

[EEG under the surface]

Epilepsy work-up is based on history and scalp EEG. Drug resistant epilepsy should be evaluated in a dedicated epilepsy surgery unit. Sometimes non-invasive studies fail to localize the epileptogenic area in focal epilepsy and then the work up can be complemented with intracranial EEG. Intracranial electrodes are implanted either in the subdural space or intraparenchymally. This is followed by one to two weeks of EEG monitoring in a specialized videotelemetry unit. Intracranial EEG helps to define the borders of the epileptogenic area for resection. The ultimate objective is to render the patient seizure free. The outcome of resective epilepsy surgery depends on the etiology of epilepsy, localization of the epileptogenic area and MR image yield.

Bilateral alterations in somatosensory cortical processing in hemiplegic cerebral palsy

AIM

In individuals with cerebral palsy (CP), cerebral insults during early development may induce profound reorganization of the motor representation. This study determined the extent of alterations in cortical somatosensory functions in adolescents with hemiplegic CP with subcortical brain lesions.

METHOD

We recorded somatosensory evoked magnetic fields in response to hand area stimulation from eight adolescents with hemiplegic CP (five females and three males; mean age 14y 6mo, SD 2y 3mo) and eight age- and sex-matched healthy comparison adolescents (mean age 15y 4mo, SD 2y 4mo). All participants in the CP group had purely subcortical brain lesions in magnetic resonance images.

RESULTS

The somatosensory representation of the affected limb was contralateral (i.e. ipsilesional), but detailed inspection of the evoked responses showed alterations bilaterally. In the primary somatosensory cortex, the representation areas of digits II and V were in both hemispheres closer to each other in participants with CP than in comparison participants [ANOVA main effect group F(1,14) =5.58; p=0.03]. In addition, the morphology of median nerve evoked fields was altered in the participants with CP.

INTERPRETATION

In hemiplegic CP, modification of the somatosensory cortical network extends beyond what would be expected based on the unilateral symptoms and the anatomical lesion. Further understanding of the functional alterations in the sensorimotor networks may aid in developing more precisely designed rehabilitation strategies.

Magnetoencephalography in neonatology

Magnetoencephalography (MEG) is a noninvasive method to study brain activity. In the previous decade the advantages of MEG -- good temporal resolution combined with good spatial resolution allowing separation of activated brain areas -- have been successfully used in gaining new information about the neonatal brain functioning. In this review, we discuss the findings from studies of spontaneous magnetoencephalogram and evoked responses to somatosensory, auditory, and visual stimulation. Our group has shown that stimulation of the upper limb in neonates evokes a response sequence reflecting activation of both primary (S(I)) and secondary somatosensory (S(II)) cortices. Like in mature brains, the earliest cortical response to median nerve stimulation reflects the arrival of afferent information to S(I). However, source modeling of the subsequent activation from S(I)suggests immature cortical functioning in neonates. Another feature typical for neonates is that the S(II)response is prominent in quiet sleep, unlike in adults in whom it diminishes in sleep. Interestingly, in very prematurely-born infants, we found alterations of the somatosensory responses at both group and individual levels. MEG provides a novel way to look at brain activity in neonates and can be used to increase knowledge of the development of brain processing and its disturbances.

Increasing the efficiency of neonatal MEG measurements by alternating auditory and tactile stimulation

OBJECTIVE

To evaluate the possible effect of intervening auditory stimulation on somatosensory evoked magnetic fields in newborns.

METHODS

We recorded auditory and tactile evoked responses with magnetoencephalography (MEG) from two groups of healthy newborns. One group (n=11) received only tactile stimuli to the index finger, the other (n=11) received alternating tactile and auditory (vowel [a:] with 300-ms duration) stimuli. The interval between subsequent tactile stimuli was always 2 s. We analyzed the equivalent current dipoles (ECDs) of the main auditory and somatosensory responses.

RESULTS

The ECDs of the tactile responses agreed with activation of the primary somatosensory cortex at ∼60 ms and the secondary somatosensory region at ∼200 ms. The source of the auditory response (∼250 ms) was clearly distinct from those to tactile stimulation and in line with auditory cortex activation. The intervening auditory stimulation did not affect the strength, latency, or location of the ECDs of the tactile responses.

CONCLUSIONS

Auditory and tactile MEG responses from newborns can be obtained in one measurement session.

SIGNIFICANCE

The alternating stimulation can be used to shorten the total measurement time and/or to improve the signal to noise ratio by collecting more data.

Somatosensory-evoked magnetic fields in examining lip area in speech-disordered children

Magnetoencephalography (MEG) is a modern neurophysiological method to study brain activation after sensory stimulation. We aimed at determining the feasibility of MEG and somatosensory-evoked magnetic fields (SEFs) in assessing the lip area in speech-disordered children undergoing oral plate therapy (OPTH) to improve their articulation. Seven subjects (age range, 6-11 years) participated in the study. The speech was perceptually assessed, and the SEFs to tactile stimulation of the lip area were recorded before and after OPTH. Two patients did not attend the posttreatment MEG recording. Clinical perceptual analysis showed remarkable improvement of speech of the studied children after OPTH. Somatosensory-evoked magnetic fields were successfully recorded in 4 of these children, but no constant changes in the responses were found after the therapy.With this small number of patients, the possible modifications in the functioning of the cortical somatosensory area of the lip after OPTH remained undetected. The present method is, however, technically applicable in studying cortical responses to lip stimulation in speech-disordered children. Further studies using stimulation inside the mouth may provide more insight to the cortical effects of OPTH.

Thalami and corona radiata in juvenile NCL (CLN3): a voxel-based morphometric study

Juvenile neuronal ceroid lipofuscinosis (CLN3) is characterized by progressive cerebral atrophy. The purpose of this study was to re-evaluate the three-dimensional magnetic resonance (3D-MR) images of patients with CLN3 using voxel-based morphometry (VBM) to achieve a detailed understanding of the affected brain regions. T1-weighted 3D-MR images of 15 patients with CLN3 (age range: 12-25 years, mean age 17.6 years) and 15 age- and sex-matched controls were analyzed using VBM. VBM showed strikingly focal alterations in the brains of CLN3 patients: the gray matter volume was significantly decreased in the dorsomedial part of the thalami of CLN3 patients. In addition, the volume of the white matter was significantly decreased in the corona radiata, containing cortical efferents and afferents in the transition between the internal capsule and the subcortical white matter. These data suggest that the dorsomedial part of the thalamus and the corona radiata may have a central, previously unrecognized role in the pathogenesis of CLN3.

Neonatal SEP - back to bedside with basic science

Scalp-recorded somatosensory evoked potentials (SEPs) have been successfully used in neonatal assessment for several decades. The current routine SEP paradigm is markedly predictive for future cerebral palsy (CP) or other neurocognitive sequelae in brain-injured babies. Recent advances in basic science have dramatically increased our knowledge about structural-functional development of SEP-related brain mechanisms. It has thereby become apparent that preterm SEP differs from that in more mature counterparts in that it also comprises responses from transient brain structures, and hence being unique to the preterm period. It is now obvious also that several aspects in the current SEP paradigm, ranging from the type of stimulation to the methods of recording and analysis, are suboptimal for preterm babies. Recent progress in recording and analysis techniques have made it possible to combine SEP studies with EEG recordings, as well as to implement advanced analyses (e.g. time-frequency analysis) into routine practice. This review summarizes literature from relevant areas in basic science, and proposes a novel, integrated approach in neonatal SEP studies in order to significantly increase the fidelity of testing somatosensory system.

Immaturity of somatosensory cortical processing in human newborns

The development of the early component of somatosensory evoked potentials (SEPs) from the neonatal N1 to adult N20 response has previously been described. The main emphasis has been on the change in the response latency during maturation. We used magnetoencephalography (MEG) to characterize the cortical generators of the N1 and the subsequent response in healthy human newborns. Furthermore, we studied the maturation of tactile processing according to responses evoked by tactile stimulation of the index finger in newborns, 6-month-old babies and adults. This study provides evidence of specific differences in the somatosensory processing in neonates compared to that in adults. Although the initial cortical response to electrical median nerve stimulation in the newborns was similar in field distribution to the corresponding N20m in adults, the subsequent major deflection in the response waveform had the opposite polarity. Similar immaturity in cortical processing was seen in the tactile evoked fields in both the newborns and the 6-month-old infants compared with the adults. Our results indicate that although the somatosensory pathway in full-term newborns is sufficiently developed to supply the brain with tactile information, the cortical neuronal networks for processing the input may not function in the same way as in adults.

Spatial dynamics of population activities at S1 after median and ulnar nerve stimulation revisited: An MEG study

In a number of studies, magnetoencephalography (MEG) has been successfully employed in localizing cortical neural population activities after stimulation of peripheral nerves. Little attention has been paid, however, to the spatiotemporal dynamics of these activations within the primary somatosensory cortex (SI). Here we report on the activation sequence at the right SI after left median and ulnar nerve stimulation. The results show that at least three macroscopically separable sources within or near SI are activated within 100 ms after the stimulus, corresponding to the somatosensory evoked field (SEF) deflections N20m, P35m and P60m. As P60m was localized significantly more posteriorly and also tended to be deeper than the two earlier deflections, its underlying source may be more extensive than during N20m and P35m, and it may get contribution from the postcentral gyrus and sulcus, possibly Brodmann areas 1 and 2. The source separation between the neural populations activated by the 2 nerves was 12 mm during N20m, 6 mm during P35m and 4 mm during P60m. Thus, at longer latencies, the centers of gravity of the activations were closer to each other for the 2 nerves. We argue that this reflects spreading of the activation with time from the site of initial excitation to encompass larger and more overlapping neural populations at longer latencies.

Trigeminal somatosensory evoked magnetic fields to tactile stimulation

OBJECTIVE

To characterise the activation of the contra- and ipsilateral primary somatosensory cortex (SI) after tactile stimulation of the face.

METHODS

Trigeminal somatosensory evoked magnetic fields (TSEFs) were recorded after tactile stimulation of the lower lip, cheek, chin and forehead in 11 healthy subjects. The responses were determined visually from the waveforms and modelled with equivalent current dipoles (ECDs).

RESULTS

Contralateral SI responses were evoked in all subjects after lip stimulation, and in 91% and 64% after right and left cheek, 73% and 82% after chin and 64% and 27% after forehead stimulation. The responses usually showed an early double-peak wave pattern, the underlying sources localising to the SI. In addition, altogether 37 ipsilateral SI responses were evoked in eight subjects. Fourteen of these responses were amenable to ECD modelling and localised to ipsilateral SI.

CONCLUSIONS

Tactile stimulation of the lip area reliably activates the contralateral SI in normal subjects, but the success rate for other trigeminal areas is lower. Ipsilateral responses can be present after stimulation of any of the trigeminal branches in normal subjects.

SIGNIFICANCE

Recording of TSEFs after tactile stimulation of particularly the lip area provides a non-invasive technique to study the function of the trigeminal nerve.