Electroenceph Clin Neurophysiol Research Articles

Reversible Carbamazapine Encephalopathy With Frontal Intermittent Rhythmic Delta Activity

Reversible Carbamazapine Encephalopathy With Frontal Intermittent Rhythmic Delta Activity

Reversible Carbamazapine Encephalopathy With Frontal Intermittent Rhythmic Delta Activity

Reversible Carbamazapine Encephalopathy With Frontal Intermittent Rhythmic Delta Activity

Benign EEG Patterns: Is there More to Learn?

Prevalence of Benign Epileptiform Variants. Santoshkumar B, Chong JJ, Blume WT, McLachlan RS, Young GB, Diosy DC, Burneo JG, Mirsattari SM. Clin Neurophysiol 2009;120(5):856–861. OBJECTIVE: There are numerous distinctive benign electroencephalographic (EEG) patterns which are morphologically epileptiform but are non-epileptic. The aim of this study was to determine the prevalence of different benign epileptiform variants (BEVs) among subjects who underwent routine EEG recordings in a large EEG laboratory over 35 years. METHODS: We retrospectively studied the prevalence of BEVs among 35,249 individuals who underwent outpatient EEG recordings at London Health Sciences Centre in London, Ontario, Canada between January 1, 1972 and December 31, 2007. The definitions of the Committee on Terminology of the International Federation of Societies for EEG and Clinical Neurophysiology (IFSECN) were used to delineate epileptiform patterns (Chatrian et al. A glossary of terms most commonly used by clinical electroencephlographers. Electroenceph Clin Neurophysiol 1974;37:538–48) and the descriptions of Klass and Westmoreland [Klass DW, Westmoreland BF. Nonepileptogenic epileptiform electroenephalographic activity. Ann Neurol 1985;18:627–35] were used to categorize the BEVs. RESULTS: BEVs were identified in 1183 out of 35,249 subjects (3.4%). The distribution of individual BEVs were as follows: benign sporadic sleep spikes 1.85%, wicket waves 0.03%, 14 and 6 Hz positive spikes 0.52%, 6 Hz spike-and-waves 1.02%, rhythmic temporal theta bursts of drowsiness 0.12%, and subclinical rhythmic electrographic discharge of adults in 0.07%. CONCLUSION: The prevalence of six types of BEVs was relatively low among the Canadian subjects when compared to the reports from other countries.

Prevalence of benign epileptiform variants

There are numerous distinctive benign electroencephalographic (EEG) patterns which are morphologically epileptiform but are non-epileptic. The aim of this study was to determine the prevalence of different benign epileptiform variants (BEVs) among subjects who underwent routine EEG recordings in a large EEG laboratory over 35 years. We retrospectively studied the prevalence of BEVs among 35,249 individuals who underwent outpatient EEG recordings at London Health Sciences Centre in London, Ontario, Canada between January 1, 1972 and December 31, 2007. The definitions of the Committee on Terminology of the International Federation of Societies for EEG and Clinical Neurophysiology (IFSECN) were used to delineate epileptiform patterns (Chatrian et al. A glossary of terms most commonly used by clinical electroencephlographers. Electroenceph Clin Neurophysiol 1974;37:538-48) and the descriptions of Klass and Westmoreland [Klass DW, Westmoreland BF. Nonepileptogenic epileptiform electroenephalographic activity. Ann Neurol 1985;18:627-35] were used to categorize the BEVs. BEVs were identified in 1183 out of 35,249 subjects (3.4%). The distribution of individual BEVs were as follows: benign sporadic sleep spikes 1.85%, wicket waves 0.03%, 14 and 6 Hz positive spikes 0.52%, 6 Hz spike-and-waves 1.02%, rhythmic temporal theta bursts of drowsiness 0.12%, and subclinical rhythmic electrographic discharge of adults in 0.07%. The prevalence of six types of BEVs was relatively low among the Canadian subjects when compared to the reports from other countries. BEVs are relatively uncommon incidental EEG findings. Unlike focal epileptic spikes and generalized spike-and-waves, BEVs do not predict the occurrence of epilepsy. Accurate identification of the BEVs can avoid misdiagnosis and unnecessary investigations.

Toward enhanced P300 speller performance

This study examines the effects of expanding the classical P300 feature space on the classification performance of data collected from a P300 speller paradigm [Farwell LA, Donchin E. Talking off the top of your head: toward a mental prosthesis utilizing event-related brain potentials. Electroenceph Clin Neurophysiol 1988;70:510–23]. Using stepwise linear discriminant analysis (SWLDA) to construct a classifier, the effects of spatial channel selection, channel referencing, data decimation, and maximum number of model features are compared with the intent of establishing a baseline not only for the SWLDA classifier, but for related P300 speller classification methods in general. By supplementing the classical P300 recording locations with posterior locations, online classification performance of P300 speller responses can be significantly improved using SWLDA and the favorable parameters derived from the offline comparative analysis.

Motor Unit Conduction Velocity Distribution Estimation From Evoked Motor Responses

Action potentials travel along the muscle fibers with a specific conduction velocity that depends on their structural and functional properties. Only the estimation of muscle conduction velocity distribution (MCVD) may be able to depict this propagation heterogeneity. Based on the method proposed by Cummins et al. (Electroenceph Clin Neurophysiol, 46:647-658, 1979) to estimate nerve conduction velocity distribution (NCVD), the present paper proposes a method that modifies the Cummins' approach to make it suitable for MCVD estimation from electrically evoked motor responses. The MCVD estimation algorithm was first assessed by means of simulated signals in order to control all signal features during the optimization process. Simulations showed that estimated distributions were very close to the true ones when taking into account the specificities of the muscle action potential, due to its generation and extinction (MSE divided by 5 on distribution standard deviation). This method was then applied to real signals. Elicited motor responses were recorded on the biceps brachii of healthy subjects either during repeated maximal stimulations at 20 Hz or during increasing intensity stimulations at 1 Hz. MCVD estimates were used to analyze fatigue and motor unit recruitment processes, respectively.

Spatial enhancement of EEG traces by surface Laplacian estimation: comparison between local and global methods

Objective Surface Laplacian estimation enhances EEG spatial resolution. In this paper, we compare, on empirical grounds, two computationally different estimations of the surface Laplacian. Methods Surface Laplacian was estimated from the same monopolar data set with both Hjorth's method [local; Electroenceph Clin Neurophysiol 39 (1975) 526] as modified by MacKay [Electroenceph Clin Neurophysiol 56 (1983) 696] and with spherical spline interpolation [global; Electroenceph Clin Neurophysiol 72 (1989) 184]. Results The grand averages computed with the two methods proved to be very similar but differed markedly from the monopolar ones. The two different computations were highly correlated, presented low relative errors and allowed to evidence comparable experimental effects. Conclusions These results suggest that Hjorth's method and spherical spline interpolation convey similar topographic and chronometric informations. Significance We provide empirical evidence that local and global methods of surface Laplacian estimation are equivalent to improve the spatial resolution of EEG traces. Global methods allow to explore the scalp topography and local methods allow to spare time in electrode setting that can be useful for studies on special populations (i.e. children, aged subjects) and for clinical purposes.

Properties of after-discharges from cortical electrical stimulation in focal epilepsies.

This study sought to determine whether certain aspects of after-discharges (ADs) obtained during cortical functional mapping provide better correlations between stimulus site and that of spontaneous seizures. Secondly, we wished to determine the percentage of stimulations evoking ADs and, of these, the percentage which clearly involves more than one electrode position, potentially inaccurately localizing cortical function. Thirdly, we wished to quantify the incidences of the several AD morphologies described by Jasper [in: Epilepsy and the functional anatomy of the human brain, 1954, p. 183; p. 692] and to assess whether certain morphologies had a greater tendency to evolve in frequency or morphology. In these 29 patients requiring invasive recordings to determine principal epileptogenic areas, only subdural strips were placed in 19 patients, only grids in 2 patients, and both in 8 patients. A median of 21 electrodes per patient was stimulated of a median of 63 electrodes placed, with the following parameters: biphasic, monopolar, 50 Hz, 0.3 ms pulse duration, 1.5-18 mA. Coverage involved the frontal and parietal lobes (9 patients), frontal parietal temporal lobes (8), frontal temporal (3), temporal (2), occipital (2) and occipital temporal (2) with other combinations in 3 additional patients. Classification of AD morphologies was determined by a pilot study using IFSECN definitions [Electroenceph clin Neurophysiol 1974;37:538] and descriptions by Jasper [in: Epilepsy and the functional anatomy of the human brain, 1954, p. 183] and Gloor [in: Advances in neurology, vol. 8, 1975; p. 59]. Four hundred and two ADs (12%) were elicited by 3358 trains of electrical stimuli of which 260 (65%) clearly involved more than only the stimulated electrode position. Thus, 260 (8%) of 3358 stimulations evoked an AD that could mislocalize cortical function. The proportion of stimulating electrodes eliciting ADs ranged among patients from 4 to 83% (median 33%). Polyspike bursts and sequential spikes were the most common AD morphologies. Ten percent of ADs evolved in morphology, frequency or both. Evolution occurred more commonly (44%) with rhythmic waves than with other AD morphologies (7%). Neither evolving ADs, ADs producing clinical seizures, or ADs exceeding 10 s correlated topologically with spontaneous seizure origins. Although occurring in a minority of cortical electrical stimuli, ADs may involve more than the stimulus site and therefore may inaccurately localize cortical function. Our material failed to disclose any consistent relationship between the site of stimulus eliciting ADs and that of spontaneously appearing seizures, even when certain aspects of such ADs were analysed. These data illustrate the need for scrutiny of the post-stimulus electrocorticogram for ADs and particularly those involving extra stimulus sites. Whether varying the stimulus parameters prospectively will disclose a better seizure localizing value for ADs remains to be determined.

Functional connectivity revealed by single-photon emission computed tomography (SPECT) during repetitive transcranial magnetic stimulation (rTMS) of the motor cortex.

In the present study, we studied effects of 1 Hz repetitive transcranial magnetic stimulation (rTMS) over the left primary motor cortex (M1) on regional cerebral blood flow (rCBF) using single-photon emission computed tomography (SPECT). SPECT measurements were carried out under two experimental conditions: real and sham stimulation. In sham stimulation, to exclude other components besides currents in the brain in rTMS, we applied sound and electrical stimulation to the skin of the head. 99mTc-ethyl cysteinate dimer was injected during the real or sham stimulation. Images were analyzed with the statistical parametric mapping software (SPM99). Relative differences in adjusted rCBF between two conditions were determined by a voxel-by-voxel paired t test. 1 Hz rTMS at an intensity of 1.1 x active motor threshold evoked increase of rCBF in the contralateral (right) cerebellar hemisphere. Reduction of rCBF was observed in the contralateral M1, superior parietal lobule (most probably corresponding to PE area in the monkey) (Rizzolatti G, Luppino G, Matelli M. Electroenceph clin Neurophysiol 1998;106:283-296), inferior parietal lobule (PF area in the monkey (Rizzolatti et al., 1998)), dorsal and ventral premotor areas (dPM, vPM) and supplementary motor area (SMA). Increase of rCBF in the contralateral cerebellum must reflect facilitatory connection between the motor cortex and contralateral cerebellum. Reduced rCBF in the contralateral M1 may be produced by transcallosal inhibitory effect of the left motor cortical activation. CBF decrease in the right PM, SMA and parietal cortex may reflect some secondary effects. Low frequency rTMS at an intensity of around threshold for active muscles can evoke rCBF changes. We demonstrated that rCBF changes could be elicited even by low frequency rTMS at such a low intensity as the threshold for an active muscle. Combination of rTMS and SPECT is one of powerful tools to study interareal connection within the human brain.

Misallocation of variance in event-related potentials: simulation studies on the effects of test power, topography, and baseline-to-peak versus principal component quantifications

Since Wood and McCarthy's simulation study (Electroenceph Clin Neurophysiol 1984;59:249–260), the use of principal component analysis (PCA) as a tool for the identification and quantification of event-related potentials (ERP) has been considered a challenge. Three relevant aspects have not been fully acknowledged in previous studies, however, and were therefore investigated in the present simulation study. Firstly, the impact of test power on the amount of variance misallocation was studied. Secondly, the impact of ERP component topography on variance misallocation was investigated. Thirdly, a systematic evaluation of variance misallocation in baseline-to-peak derived ERP measures was performed. Results based on an overall set of 2700 simulations indicate that: (a) variance misallocation is reduced to an almost acceptable level when an appropriate test power is simulated; (b) the overall amount of variance misallocation remains at an almost acceptable level when systematic topographic effects are simulated in combination with an appropriate test power; and (c) variance misallocation is in fact also a problem in baseline-to-peak measures. These findings confirm that, when used appropriately, PCA is a helpful and efficient tool for the identification and quantification of ERPs.

Conduction velocity of the spinothalamic tract following CO 2 laser stimulation of C-fibers in humans

Pain-related somatosensory-evoked potential following CO 2 laser stimulation (laser-evoked potential (LEP)) is now used not only for research objectives, but also for clinical applications. Estimating the conduction velocity (CV) of the spinothalamic tract (STT) by analyzing LEP following activation of Aδ-fibers (Aδ-CVSTT) by CO 2 laser stimulation has been performed previously, but estimating the CV of STT following activation of C-fibers (C-CVSTT) has not. This is the first report to estimate the C-CVSTT in humans; by using the novel method of CO 2 laser stimulation applied to tiny skin areas. The calculation method was based on that of Kakigi and Shibasaki (Electroenceph clin Neurophysiol 80 (1991) 39) who measured Aδ-CVSTT by conventional CO 2 laser stimulation. The C-CVSTT ranged between 1.4 and 4.0 m/s, and its mean±SD was 2.9±0.8 m/s. This C-CVSTT was significantly slower than the Aδ-CVSTT, which ranged approximately from 10 to 21 m/s. The nociceptive signal of the C-fibers in STT is probably conveyed by unmyelinated axons of projection neurons to reach the thalamus. Our findings provide the first physiological evidence of the signals ascending through unmyelinated axons in the spinal cord in humans. In addition, estimating C-CVSTT and Aδ-CVSTT combined with conventional methods to measure the CV of the posterior column using electrical stimulation should be useful and have important clinical applications, particularly in patients with spinal cord lesions showing various kinds of sensory disturbances.

Sleep stage dependant changes of the high-frequency part of the somatosensory evoked potentials at the thalamus and cortex

Objectives: It is known that the high-frequency oscillations (above 400 Hz) of the somatosensory evoked potentials (SEPs) diminish during sleep while the N20 persists (Neurology 38 (1988) 64; Electroenceph clin Neurophysiol 70 (1988) 126; Electroenceph clin Neurophysiol 100 (1996) 189). We investigated possible differential effects of sleep on the 600 Hz SEPs at the thalamus and cortex. Methods: SEPs from 10 subjects were recorded using 64 channels following electric stimulation at the wrist during awake state and sleep stages II, IV and REM. Dipole source analysis was applied to separate brain-stem, thalamic and cortical activity in the low-frequency (20–450 Hz) and the high-frequency (450–750 Hz) part of the signal. Results: The low-frequency SEPs showed a non-significant increase of the latency of the N20 and a bifid change of the waveform in 3 subjects. The high-frequency SEPs showed a significant decrease of their amplitude at the level of the thalamus and cortex but not at the brain-stem. This decrease in amplitude at the thalamus and cortex were significantly correlated. There was no effect on the latency of the signal. In addition, at the cortex, differential effects on early and late parts of the 600 Hz oscillations were found by time-frequency analysis using a wavelet transformation. Conclusions: Sleep dependent decrease of the high-frequency SEPs were first observed at the thalamus pointing to the known function of the reticular thalamic nucleus regulating arousal. The results presented here provide further evidence for a thalamic origin of the 600 Hz oscillations. In addition, on the basis of the differential effects on early (up to the N20 peak) and late (between 20 and 25 ms) parts of the signal, at least one intracortical generator of these oscillations is proposed. In general, the high-frequency SEPs (600 Hz oscillations) are supposed to reflect activity of a somatosensory arousal system.

A simple method for estimating conduction velocity of the spinothalamic tract in healthy humans

Objectives: The object of this study was to establish a method for estimating the conduction velocity (CV) of the spinothalamic tract (STT) in relation to clinical application. Methods: The CV of the STT was estimated by an indirect method based on that reported by Kakigi and Shibasaki in 1991 (Kakigi R, Shibasaki H. Electroenceph clin Neurophysiol 80 (1991) 39). Laser-evoked potentials (LEP) were measured in 8 subjects following hand (LEPH) and foot (LEPF) laser stimulation. The conduction times recorded at the scalp (P340, P400 and N150 potentials) were considered as the summation of peripheral and central components. The peripheral conduction times were calculated by measuring the latency of the electrical cutaneous silent period (from the same stimulus site of LEPs), corrected for F- and M-wave latency values. Results: The CV of the STT ranged between 8.3 and 11.01 m/s and its mean value was found to be approximately 9.87±1.24 m/s. The CV of the STT obtained by the N150 latencies overlapped that obtained by the P340/P400 latencies. Conclusions: Our data suggest that our method appears appropriate and useful for practical clinical purposes, furnishing an additional tool for investigating the physiological function of small-fiber pathways.

Reciprocal modulation of somatosensory evoked N20m primary response and high-frequency oscillations by interference stimulation

Objectives: We examined whether the inverse relation between somatic evoked N20m primary response and high-frequency oscillations during a wake-sleep cycle (Hashimoto, I., Mashiko, T., Imada, T., Somatic evoked high-frequency magnetic oscillations reflect activity of inhibitory interneurons in the human somatosensory cortex, Electroenceph clin Neurophysiol 1996;100:189-203) holds for interference stimulation.Methods: Somatosensory evoked fields (SEFs) from 14 subjects were measured following electric median nerve stimulation at the wrist with, and without, concurrent brushing of the palm and fingers. SEFs were recorded with a wide bandpass (0.1–1200 Hz) and then N20m and high-frequency oscillations were separated by subsequent low-pass (<300 Hz) and high-pass (>300 Hz) filtering.Results: The N20m decreased dramatically in amplitude during interference stimulation. In contrast, the high-frequency oscillations moderately increased in number of peaks.Conclusions: These results demonstrate the presence of an inverse relation between N20m and high-frequency oscillations for interference stimulation. We speculate that the high-frequency oscillations represent a localized activity of GABAergic inhibitory interneurons of layer 4, characterized by a high-frequency spike burst (200–1000 Hz) without adaptation, and that the continuous interference stimulation induces tonic excitation of the interneurons, leading to a facilitation of responses to the coherent afferent volley elicited by the median nerve stimulation (bottom-up mechanism). On the other hand, refractoriness of the pyramidal neurons caused directly by interference stimulation along with an enhanced feed-forward inhibition from the interneurons will lead to a decrease of N20m amplitude.

Input-output organization of the foot motor area in humans

Objective: A well-organized input-output relation similar to that of the monkey motor cortex has been demonstrated in the human hand motor area (Terao Y, Ugawa Y, Uesaka Y, Hanajima R, Gemba-Shimizu K, Ohki Y, Kanazawa I. Input-output organization in the hand area of the human motor cortex, Electroenceph clin Neurophysiol 1995;97:375-381). The aim of this study is to investigate the input-output organization of the human foot motor area. Methods: We studied the effect of tactile stimuli given to the toe tip on the sizes of following responses; motor evoked potentials (MEPs) elicited by transcranial magnetic or electrical stimulation (TMS or TES) over the motor cortex and magnetic stimulation at the foramen magnum level. Results: Air stimuli applied to the toe tip facilitated magnetically evoked MEPs of mainly the muscle attached to that toe, although a less prominent facilitation was also noted in muscles attached to the adjacent toes. Neither responses evoked by TES, nor those by stimulation at the foramen magnum level, were affected by air stimuli. These results suggest that the observed facilitatory effect occurs at the cortical level. Conclusion: A fairly well-organized input-output relation is present also in the foot motor area in humans, although the facilitatory effect is not so topographically restricted as is noted for the hand motor area.

P3a of event-related potential in chronic methamphetamine dependence.

To investigate the psychophysiological features of methamphetamine (MAP) dependence, we recorded auditory event-related potentials (ERPs) in 15 patients with MAP dependence and in 15 age-matched normal controls. ERPs were recorded during a standard oddball task and a read task similar to those employed by Squires et al. (Squires NK, Squires KC, Hillyard SA [1975] Two varieties of long-latency positive waves evoked by unpredictable auditory stimuli in man. Electroenceph Clin Neurophysiol 38:387-401). The patients with MAP dependence showed reduced P3a amplitude and area in the read task and delayed P3b latency with normal P3b amplitude and area in the oddball task. These results suggest that central noradrenergic dysregulation may persist after the remission of acute psychotic symptoms in MAP psychosis and that chronic MAP dependence would produce impairment of the frontal cortex.

Frontal component of the somatosensory evoked potential

AbstractElectric stimulation of the median nerve at the wrist evokes a series of electric potentials that can be recorded from the scalp or directly from the cortex. These somatosensory evoked potentials (SEP) include a parietal negativity with a maximum 20 ms after the stimulus, which originates in the somatosensory cortex, probably area 3b (Allison et al. [1991a], Brain 114:2465–2503 and Desmedt et al. [1987], Electroenceph Clin Neurophysiol 68:1–19). Thirty milliseconds after the stimulus, a negative potential (N30) occurs at frontal recording sites. Recently it was observed that the amplitude of this potential is altered in patients with dystonia, Parkinson's disease, and Huntington's chorea. It has been argued that the N30 potential stems from cortical areas other than the somatosensory cortex, for example, the supplementary motor area. We used multichannel recordings to investigate the scalp distribution of the N20 and the N30 potentials in healthy subjects. We found that the N20 as well as the N30 potentials were accompanied by a corresponding positivity at frontal and parietal recording sites, respectively. The N20/P20 and the N30/P30 potential fields had a mirrorlike appearance, and both showed a polarity reversal near the central sulcus. This and the results of correlation analyses led us to the conclusion that the N30 generator is located near the central sulcus. © 1995 Wiley‐Liss, Inc.