Extreme somatosensory evoked potentials (ESEPs) elicited by tapping of hands or feet in children: a somatosensory cerebral evoked potentials study

Six children with tactile-evoked spikes in the EEG, also defined as extreme somatosensory evoked potentials (ESEPs), underwent an SEPs study in order to define the characteristics of such evoked potentials. Short-latency SEPs showed normal mean latency and amplitude values. Mid- or long-latency SEPs of abnormally high amplitude were recorded after stimulation of one or more extremities. Such extreme responses which showed the same reactivity proper to normal long-latency SEPs could be considered to correspond to the evoked spikes in the EEG.     

Somatosensory evoked potential and EEG in children with focal idiopathic epilepsies with and without evoked spikes by tapping of the feet or hands.

The characteristics of SEP cortical components were studied in 40 children with focal idiopathic epilepsies of childhood. Twenty children had focal idiopathic epilepsies and evoked spikes (FIE-ES) on the EEG and 20 had benign focal epilepsy of childhood with centrotemporal spikes (CTE) but without evoked spikes (ES). These data were compared with those of a control group of 20 normal children. N35 high-amplitude component was more frequent in the CTE group than in the control group (p < 0.001). P98 showed high amplitude in 50% of the children of FIE-ES group, and in none of the CTE and control groups (p < 0.001). The P98 high amplitude component was more common in the FIE-ES group than in the other groups, and so was the N35 high amplitude component in the CTE group. Lateralization of high-amplitude components of N35 in the CTE group and of P98 in FIE group was not correlated with lateralization of epileptiform activity and evoked spikes. Based on our findings, there are SEPs cortical component differences in childhood focal idiopathic epilepsies according to occurrence or absence of ES.     

伴有中央-颞区局灶棘波儿童良性癫痫的动态脑电图研究

目的 探讨伴有中央-颞区局灶棘波儿童良性癫痫(BECT)的脑电图特征.方法 对115例BECT患儿进行动态脑电图检查,并对检查结果及临床表现进行分析.结果 BECT主要表现为面部抽搐、流涎、喉咙发声、发作性肢体阵挛或强直,发作与睡眠密切相关.脑电图背景活动正常,发作间期脑电图一侧或双侧中央-颞区出现棘波或尖波,可向其它部位扩散,还可从一侧半球转移至对侧半球.入睡后局灶放电频率明显增多.结论 BECT临床发作和睡眠密切相关.脑电图是诊断本病的主要依据,动态脑电图可提高脑电图诊断的阳性率.     

Evoked parietal spikes in the electroencephalogram and febrile convulsions

In a population of 2307 children, 69 (2.99%) showed in the EEG high-voltage evoked potentials (evoked spikes) elicited by tapping on the feet or hands. Febrile convulsions were mentioned in 226 cases, and 13 of them showed the evoked spikes in the EEG and were otherwise neurologically and psychologically normal. Association between febrile convulsions and evoked spikes was observed, mainly when EEG showed also epileptiform activity of parietal localization. These EEG features are probably of functional rather than organic nature, and with possible genetic mechanisms involved. Longitudinal studies of children with febrile convulsions and evoked spikes in the EEG are necessary to verify a possible high risk of developing epilepsy not predicted on clinical data.     

Benign Epilepsy of Childhood With Centrotemporal Spikes

Summary: Benign epilepsy of childhood with centrotemporal spikes (BECT) is the most common partial epilepsy syndrome in the pediatric age group, with an onset between age 3 and 13 years. The typical presentation is a partial seizure with paresthesias and tonic or clonic activity of the lower face associated with drooling and dysarthria. Seizures commonly occur at night and may become secondarily generalized. They are usually infrequent and may not require antiepileptic drugs but, if treated, they tend to be easily controlled. Children with BECT are neurologically and cognitively normal. The EEG shows characteristic high-voltage sharp waves in the centrotemporal regions, which are activated with drowsiness and sleep. In this typical form, BECT is easily recognized. However, atypical cases are common and the definition of BECT can become blurred. Although further investigations are not required in cases with typical clinical and EEG findings and normal neurologic examinations, neuroimaging studies may be required in atypical cases to rule out other pathology. The long-term medical and psychosocial prognosis of BECT is excellent, with essentially all children entering long-term remission by mid-adolescence.     

Somatosensory evoked spikes and epileptic seizures: a study of 385 cases.

We examined 385 children whose EEG showed high voltage potentials evoked by taps applied to one or both feet or hands (SES). The relationship between characteristics of SES and the occurrence of epileptic seizures and the characterization of epileptic syndromes were studied. Ninety-one children (23.6%) had epilepsy, 42 (10.9%) had only febrile convulsions and 252 children had other complaints. Epilepsy occurred in a higher proportion of cases when: SES by foot tapping were multiphasic, with high amplitude or SES were obtained by hand stimulation and there was spontaneous epileptiform activity in the EEG. The following epileptic syndromes were diagnosed: benign childhood epilepsy with centrotemporal spikes in 21 cases, benign epilepsy of childhood with occipital paroxysms in 2, benign psychomotor epilepsy in 1, "partial idiopathic others" in 43, generalized idiopathic in 8, symptomatic epilepsies in 13 and undetermined in 3 cases. In most cases SES were observed in children without evidence of cerebral organic lesion, suggesting the existence of an age-related, functional mechanism. Some characteristics of SES and the occurrence of spontaneous epileptiform activity showed a positive association with epileptic seizures. SES occurred in different types of partial and generalized epilepsies of childhood but in nearly 50% of the cases with epilepsy, there was a benign condition involving mainly the parietal lobe with versive, unilateral and sleep-generalized seizures.     

Contribution of motor cortex in generation of evoked spikes in patients with benign rolandic epilepsy.

OBJECTIVES: Among the different kinds of rolandic epilepsy there is a form of benign epilepsy with centrotemporal spikes (BECT) presenting the peculiar characteristic of evoking rolandic paroxysmal activity, characterized by a spike followed by a slow wave, using electrical stimulation of the fingers. METHODS: We evaluated 7 patients suffering from BECT presenting evoked scalp activity by electrical stimulation of the fingers of the hand. Electrical stimulation was performed using a pair of ring electrodes applied to the thumb. The motor evoked potentials (MEPs) were elicited in hand muscles by transcranial magnetic stimulation (TMS) and were conditioned by the same electrical digital stimulation producing the evoked spikes at interstimulus intervals ranging from 10 to 200 ms. RESULTS: Digital stimulation in epileptic patients produced an increase in MEP amplitude substantially above the normal ranges. MEP facilitation showed a time course overlapping the ascending phase and peak of the evoked spike, whereas no significant MEP changes were found during the early positive peak and the descending phase of the spike, or during the following slow wave. CONCLUSIONS: Several considerations support the hypothesis that the short-lasting M1 facilitation is related to the spread of an abnormal hypersynchronous discharge of the S1 neurones to functionally related motor areas via cortico-cortical connections.     

Somatosensory evoked potentials and action myoclonus

The authors studied the somatosensory evoked potentials (SEPs) in 16 cases of myoclonic encephalopathies: 8 cases of dyssynergia cerebellaris myoclonica (DCM); 2 cases of dyssynergia cerebellaris progressiva (DCP); 2 cases of Lafora's disease; 1 case of ceroid lipofuscinosis; 3 unclassifiable myoclonic syndromes. The mean age of the patients was 18 years and the mean duration of pre-study evolution was 10 years. All the patients had been treated by anticonvulsant drugs (phenobarbital, valproic acid, benzodiazepines). The amplitude of the complex P1N2 at the level of the contralateral parietal cortex, with stimulation of the median nerve at the wrist, was found to be enlarged in only 6 cases and giant responses (over 40 microV) were obtained in 2 cases. Only half of the patients with DCM presented a high amplitude response. There was no correlation either with clinical parameters (and in particular, certain patients with marked action myoclonic jerks have a normal SEP), or with the EEG data: on the contrary, the amplitude variations of the SEPs are most often similar to variations of the visual evoked potentials.     

Frontal and parietal components of enhanced somatosensory evoked potentials: a comparison between pathological and pharmacologically induced conditions

Pathologically enhanced somatosensory evoked potentials (giant SEPs) were recorded in 10 patients with cortical myoclonus of various origins. With non-cephalic reference electrodes a giant frontal negativity corresponding to normal N30 was found over the contra- and ipsilateral hemispheres which was not simply a phase reversal of the well-known enhanced parietal P25. The preceding far-field P14, parietal N20 and frontal P22 were of normal size. A similar result was found when SEPs were studied during the action of etomidate, an ultrashort-acting non-barbiturate hypnotic which produced a marked increase of the parietal P25 and frontal N30 after intravenous administration. These increased components, on the other hand, were abolished when recording was repeated immediately after application of electroconvulsive shock whereas P14, N20, and P22 remained more or less unchanged in both conditions. Our results indicate that there are neuronal elements in the sensorimotor cortex which are more resistant to influences such as narcotic drugs and seizure activity than others, being highly modifiable by these alterations. It is speculated whether these highly modifiable cortical systems are those in which giant SEPs, as well as pharmacologically increased SEP components, arise.     

伴中央颞区棘波的儿童良性癫痫典型及非典型病例探讨

目的 探讨ＢＥＣＣＴ典型与非典型特征,以提高对该病的认识。方法 分别５６例ＢＥＣＣＴ临床发作形式、ＥＥＧ表现、影像学及治疗资料。结果 ５６例中典型者２３例（４１．０７％）;不典型病例３３例（５８．９３％）,其中临床发作形式不典型１６例（２８．５７％）,ＥＥＧ不典型２５例（４４．６４％）。头ＣＴ及ＭＲＩ检查正常４６例,轻度异常１０例。卡马西平及丙戊酸对治疗典型和非典型的ＢＥＣＣＴ均有效,以卡马西平为优。结论 ＢＥＣＣＴ的诊断应建立在对发病年龄、发作时间及形式、发作间期ＥＥＧ综合分析基础上,可以有不典型的发作。曾接受ＡＥＤｓ治疗者ＥＥＧ可能不典型。     

Time course of frontal somatosensory evoked potentials. Relation to L-dopa plasma levels and motor performance in PD.

OBJECTIVE: To verify whether the change in L-dopa plasma levels after a single dose of carbidopa/L-dopa 50/200 (controlled-release) transiently modifies frontal components of somatosensory evoked potentials (SEPs) in patients with PD in parallel with improvement of motor performance. BACKGROUND: Apomorphine, a potent dopamine-agonist drug, transiently increases frontal SEP components, which may be depressed in PD; however, relationships between clinical status, frontal SEPs, and therapy are still unclear. METHODS: Nineteen PD patients (mean age 65.9 years, range 52 to 77, responders to L-dopa therapy, were studied in the same day at times T0 (baseline predose level), T1 (presumed L-dopa peak time), and T2 (end of dose-induced motor response). The following were monitored: L-dopa plasma concentration, tapping test, reaction times, peak latency (with central conduction times), and amplitude of cervical, subcortical, as well as cortical parietal and frontal SEP components elicited by median nerve stimulation of the more clinically affected arm. RESULTS: The average amplitude of frontal components of PD patients was significantly reduced at T0 with respect to control subjects. A significant and transient amplitude increase of frontal SEPs was found at T1, in parallel with the L-dopa peak concentration and improvement in motor performance (tapping and reaction times), without significant changes in amplitude of parietal SEP waves. No latency shifts were observed in brain and spinal waves. CONCLUSIONS: L-Dopa may influence the responsiveness of the parkinsonian brain as assessed by frontal somatosensory evoked potentials. The time course of these modifications coincides with that of the clinical response in the motor performance.     

Spike topography and functional magnetic resonance imaging (fMRI) in benign rolandic epilepsy with spikes evoked by tapping stimulation

We performed a spike topography study and a functional magnetic resonance imaging (fMRI) in a female patient with benign rolandic epilepsy presenting single high-amplitude evoked spikes in response to somatosensory peripheral stimulation. The stimulus was delivered to the first finger of the right hand using a tendon hammer, which evoked a single spike followed by a slow wave, showing the maximal amplitude over the left central regions. fMRI showed that the contralateral sensory cortices (S1 and S2) and the motor cortex (M I) were activated during tapping stimulation. In 3 normal subjects, tapping stimulation produced no fMRl activation. This fMRI study documents a highly focal activation of sensorimotor areas related to subclinical evoked spikes in benign rolandic epilepsy.     

Benign Familial Neonatal Convulsions Followed by Benign Epilepsy with Centrotemporal Spikes in Two Siblings

Summary: Purpose: To report on sibling cases with benign familial neonatal convulsions (BFNC) followed by benign epilepsy with centrotemporal spikes (BECT).
Methods: Case histories and EEGs were obtained for the two siblings with neonatal and subsequent epileptic seizures in one pedigree with BFNC.
Results: The family included six affected cases of BFNC in two generations: the proband, the proband's mother and two sisters, and the proband's maternal uncle and his daughter. The proband developed a generalized tonic convulsion 2 days after birth with no apparent cause and normal interictal EEG, and experienced a total of 18 episodes of tonic or clonic seizures or both by age 9 months. In the follow-up course, an EEG recording showed rolandic discharges at 2 years, and a sylvian seizure occurred at 4 years during sleep. On carbamazepine therapy, the last seizure was recorded at 9 years after a total of 11 episodes of sylvian seizures, with normal EEGs after 12 years. The proband's sister experienced nine episodes of brief tonic seizures between 7 and 9 days after birth, and also developed eight episodes of sylvian seizures from 4 to 7 years, with rolandic discharges on EEG until age 9 years. All of the family members had normal psychomotor development, with no neurologic sequelae.
Conclusions: This report of BFNC followed by BECT in sibling cases is significant in view of the genetic analysis and the classification of epilepsies and epileptic syndromes.     

Bilateral centrotemporal spikes triggered by blinking: an unusual form of sensory input with related cortical EEG activity.

OBJECTIVE: To investigate the morphology, scalp topography and temporal relationship with orbicularis oculi muscle contraction of bilateral blink related spikes (BRS) in a 7-year-old boy with chromosomopathy, mild mental retardation and left spontaneous centrotemporal spikes (SS). METHODS: The patient underwent video-polygraphic recordings with off-line analysis of SS and BRS by means of spike-averaging and orbicularis oculi contraction-locked averaging techniques respectively. EEG activity related to reflex blinking (evoked by glabellar tapping) was also studied. RESULTS: SS and BRS presented the same morphology, characterised by four peaks (P1, N1, P2, N2). SS were located over the left centroparietal regions, while BRS were placed over both left and right centrotemporoparietal regions and constantly followed the contraction of orbicularis oculi with overlapping peak latencies over C3 and C4 electrodes (P1 72 ms; N1 115 ms; P2 164 ms; N2 236 ms). Reflex blinking evoked a small waveform with the same features as BRS. CONCLUSIONS: Our findings suggest that both involuntary and reflex blinking can act as a form of sensory stimulation probably engaging similar nervous pathways and cortical sources in generating EEG abnormalities: the trigeminal system.     

Somatosensory evoked potentials following stimulation of the lower limb in cortical reflex myoclonus.

Generating mechanisms of giant somatosensory evoked potentials (SEPs) following stimulation of the posterior tibial nerve as well as the big toe were investigated in three patients with cortical reflex myoclonus. Scalp distributions of recognisable components were very similar to those in normal subjects, except that their amplitude was much larger. The tibial nerve SEPs were remarkably attenuated by interfering tactile stimulation. Therefore, the giant SEPs observed in the present cases seem to be, at least partially, due to input from cutaneous nerve fibres on the background of extremely enhanced excitability in area 3b of the primary sensory cortex where normal SEPs are generated.     

Absence of gaze direction effects on EEG measures of sensorimotor function.

OBJECTIVE: Gaze direction is known to modulate the activation patterns of sensorimotor areas as seen at the single cell level and in functional magnetic resonance imaging (fMRI). To determine whether such gaze direction effects can be observed in scalp-recorded electroencephalogram (EEG) measures of sensorimotor function we investigated somatosensory evoked potentials (SEPs) and steady state movement related cortical potentials (MRPs). METHODS: In two separate experiments, SEPs were elicited by electrical stimulation of the median nerve (experiment 1) and steady state MRPs were induced by 2 Hz tapping paced by an auditory cue (experiment 2), while subjects directed their gaze 15 degrees to the left or to the right. RESULTS: Gaze direction failed to produce any appreciable differences in the waveforms of the SEPs or MRPs. In particular, there was no effect on peak amplitude, peak latency and peak scalp topography measures of SEP and MRP components, or on spatial or temporal parameters of dipole models of the underlying cortical generators. Additional frequency domain analyses did not reveal reliable gaze-related changes in induced power at electrode sites overlying somatosensory and motor areas, or in coherence between pairs of parietal, central and frontal electrodes, across a broad range of frequencies. CONCLUSIONS: EEG measures of sensorimotor function, obtained in a non-visual motor task, are insensitive to modulatory effects of gaze direction in sensorimotor areas that are observable with fMRI.     

Scalp topography of somatosensory evoked potentials following electrical stimulation of femoral nerve

Up to 29 channels of somatosensory evoked potentials (SEPs) were recorded in 10 normal volunteers following unilateral femoral nerve (FN) and tibial nerve (TN) electrical stimulation. Typical short latency FN SEPs consisted of 6 components, P15, N19, P26, N34, P44 and N56. P15 and N19 were widely distributed on the scalp. The first localized scalp component, P26, was strictly postrolandic and distributed on the contralateral parietal scalp close to midline with a prerolandic phase reversal, N26. This scalp distribution is clearly different from the first localized potential of tibial nerve SEPs. N34 and P44 were maximal at the vertex with a distribution that spread to the ipsilateral central and parietal scalp. The amplitude of P26 increased and latency shortened with increasing stimulus intensity and both values plateaued after the stimulus intensity reached motor threshold. No correlation was found between the peak latency of P26 and body height.     

Neurophysiological signals of working memory in normal aging

To examine how neurophysiological signals of working memory (WM) change with normal aging, we recorded EEGs from healthy groups (n=10 each) of young (mean age=21 years), middle-aged (mean=47 years), and older (mean=69 years) adults. EEGs were recorded while subjects performed easy and difficult versions of a spatial WM task. Groups were matched for IQ (mean=123; WAIS-R) and practiced in task performance. Responses slowed with age, particularly in the more difficult task. Advanced age was associated with decreased amplitude and increased latency of the parietal P300 component of the event-related potential and an increase in the amplitude of a frontal P200 component. Spectral features of the EEG also differed between groups. Younger subjects displayed an increase in the frontal midline θ rhythm with increased task difficulty, a result not observed in older subjects. Age-related changes were also observed in the task-related alpha signal, the amplitude of which decreases as more neurons become involved in task-related processing. Young adults showed a decrease in alpha power with increased task difficulty over parietal regions but not over frontal regions. Middle-aged and older adults showed decreased alpha power with increased task difficulty over both frontal and parietal regions. This suggests that normal aging may be associated with changes in the fronto-parietal networks involved with spatial WM processes. Younger subjects appear to use a strategy that relies on parietal areas involved with spatial processing, whereas older subjects appear to use a strategy that relies more on frontal areas.     

Independent component analysis separates spikes of different origin in the EEG.

Independent component analysis (ICA) is a novel system that finds independent sources in recorded signals. Its usefulness in separating epileptiform activity of different origin has not been determined. The goal of this study was to demonstrate that ICA is useful for separating different spikes using samples of EEG of patients with focal epilepsy. Digital EEG samples from four patients with focal epilepsy were included. The patients had temporal (n = 2), centrotemporal (n = 1) or frontal spikes (n = 1). Twenty-six samples with two (or more) spikes from two different patients were created. The selection of the two spikes for each mixed EEG was performed randomly, trying to have all the different combinations and rejecting the mixture of two spikes from the same patient. Two different examiners studied the EEGs using ICA with JADE paradigm in Matlab platform, trying to separate and to identify the spikes. They agreed in the correct separation of the spikes in 24 of the 26 samples, classifying the spikes as frontal, temporal or centrotemporal, left or right sided. The demonstration of the possibility of detecting different artificially mixed spikes confirms that ICA may be useful in separating spikes or other elements in real EEGs.     

A follow-up study of healthy children with epileptiform EEG discharges

Fifty-two healthy elementary schoolchildren with epileptiform EEGs who were not taking anticonvulsants were followed for an average period of 3 years and 3 months. Thirty-seven had centrotemporal spikes, three had occipital spikes, one had frontal spikes, nine had generalized spike-and-wave complexes, and two had a combination of multiple spike-and-wave complexes and focal spikes. Disappearance of epileptiform discharges was observed in 65% on waking EEGs and in 45% on sleep EEGs. After 5 years, the rate of disappearance was over 80% in waking and sleep EEGs. This study confirms that most epileptiform discharges in healthy children disappear spontaneously during childhood and that age-related development and disappearance occur in healthy children who would otherwise never be subjected to EEG examination. Epileptic seizures occurred in three cases (6%). This low percentage is not considered to be an indication for treating children with epileptiform discharges with anticonvulsants. However, the risk for seizure development may be higher than in the general population. According to the literature, children with multiple spike-wave complexes have a greater tendency to develop seizures. One girl with multiple spike-wave complexes and focal spikes developed generalized tonic-clonic convulsions. Two boys with centrotemporal spikes developed benign childhood epilepsy with centrotemporal spikes (BCECS). This study confirms that some (5%) of healthy children with centrotemporal spikes, the most common epileptiform pattern in healthy children, develop BCECS.