Prospective multi-center study of an automatic online seizure detection system for epilepsy monitoring units.

OBJECTIVE: A method for automatic detection of epileptic seizures in long-term scalp-EEG recordings called EpiScan will be presented. EpiScan is used as alarm device to notify medical staff of epilepsy monitoring units (EMUs) in case of a seizure. METHODS: A prospective multi-center study was performed in three EMUs including 205 patients. A comparison between EpiScan and the Persyst seizure detector on the prospective data will be presented. In addition, the detection results of EpiScan on retrospective EEG data of 310 patients and the public available CHB-MIT dataset will be shown. RESULTS: A detection sensitivity of 81% was reached for unequivocal electrographic seizures with false alarm rate of only 7 per day. No statistical significant differences in the detection sensitivities could be found between the centers. The comparison to the Persyst seizure detector showed a lower false alarm rate of EpiScan but the difference was not of statistical significance. CONCLUSIONS: The automatic seizure detection method EpiScan showed high sensitivity and low false alarm rate in a prospective multi-center study on a large number of patients. SIGNIFICANCE: The application as seizure alarm device in EMUs becomes feasible and will raise the efficiency of video-EEG monitoring and the safety levels of patients.

EEG evidence of gender differences in a motor related CNV study.

In the present study gender differences related to the contingent negative variation (CNV) were investigated. A series of two acoustic stimuli was presented to participants across a wide age range. The first stimulus was consistent throughout the experiment whereas the second one was either a high frequency or a low frequency tone. One of them had to be answered by a button press (go condition) the other did not require any response (nogo condition). Between the first and the second tone there was a time period of two seconds in which the CNV appeared as a slow negative potential shift. Within this episode data were analysed with respect to gender differences. Statistical analysis revealed topographical differences between men and women in go conditions for both left and right index finger movements. Differences were found over frontal regions where women showed higher brain activity than men and over temporo-parietal regions where men produced higher brain activity than women. In order to explain the fact that only in "go" conditions significant gender differences occurred we introduce the phenomenon of implicit learning. Due to implicit learning assumed predictions related to S2 might have occurred from time to time. This is so, because a 50% chance for one of two different stimuli to occur leads to reasonable assumed predictions after two or more stimuli of a kind occurring in a series. The present data now provide evidence that if such assumed prediction or expectancy is directed towards an upcoming demand to act then brain activity is subject to gender differences. Further studies providing controlled sequences of "go" conditions versus "nogo" conditions have to be done to prove this idea true.

The effects of alteration of effector and side of movement on the contingent negative variation.

OBJECTIVE: The contingent negative variation (CNV) is a widespread electroencephalographic (EEG) potential that occurs during the interval between a warning stimulus and a subsequent imperative stimulus if a mental or motor response is required. The present study was designed to explore the impact of the previous trial on the CNV of the forthcoming trial, that is, how a previous movement affects brain activation preparing the next movement. Effects of alteration of finger (from index to middle, and vice versa) and hand (from left to right, and vice versa) were examined independently from each other. METHODS: CNV was recorded in 20 right-handed healthy subjects with electrodes placed at F7, F5, F3, F4, F6, F8, FC5, FC3, FC1, FC2, FC4, FC6, T7, C5, C3, C1, C2, C4, C6, T8, CP5, CP1, CP2, CP6, P7, P3, P4 and P8. In a visual/visual S1-choice paradigm, an earlier informative (S1) stimulus which instructed for side and finger of the following movement was followed 3 s later by an imperative (S2) stimulus providing the command to move. Subjects had to respond to each imperative stimulus with an appropriate button press made by brisk flexion movements with the index or middle finger of each hand. The CNV recorded in the interval between the informative and the imperative stimulus was analysed with respect to finger and hand of the present and the preceding movement. RESULTS/CONCLUSIONS: (1) A change of the side of movement is associated with a widespread increase of negativity contralateral to the currently prepared movement. (2) A change of finger is associated with a focal increase of negativity contralateral to the side of the current movement over temporoparietal and mid-parietal areas. (3) A change of finger results in a widespread increase of negativity over the left hemisphere.

The effects of alteration of effector and side of movement on movement-related cortical potentials.

The amplitude of the movement-related cortical potential (MRCP) preceding self-paced voluntary movements is larger if subjects alter between flexions of two fingers compared with repetitive movements of the same finger. However, earlier studies were confined to alternating movements between limbs only and therefore could not differentiate effects of between-limbs from within-limb alteration. The present study was designed to examine effects of alteration of finger (from index to middle, and vice versa) and hand (from left to right, and vice versa) independently from each other. MRCPs were recorded in 20 right-handed healthy young subjects with electrodes placed at Fp1, Fp2, F7, F3, F4, F8, T7, C5, C3, C1, C2, C4, C6, T8, P7, P3, P4, P8, O1 and O2. Subjects made self-paced flexion movements with the index or middle finger of each hand by pressing one out of 4 response buttons. In the alternating conditions, subjects pressed two buttons in a strictly alternating fashion. Every finger was combined with every other finger, arriving at a total of 6 alternating conditions. In the 4 regular conditions, subjects pressed a particular button repetitively across trials. The results show the following: (1) MRCPs over contralateral sensorimotor areas are higher if subjects change the side of movement than if the movements are done with the same hand repeatedly. (2) MRCPs over lateral parietal areas are higher for ipsilateral than contralateral movements in the regular conditions but also increase contralaterally after a change of the side of movement. (3) Any change of side or finger is associated with a widespread increase of negativity over the left hemisphere.

Physiological evidence of gender differences in word recognition: a magnetoencephalographic (MEG) study.

Magnetic field recordings were made in order to describe brain processes during a word recognition experiment. We investigated 26 healthy young subjects (14 females) and focused on gender differences related to recognition performance and brain activity. From about 200 ms to 350 ms after word onset the event-related field (ERF) patterns differed significantly between women and men, although the mean recognition performances did not. Differences were due to different strengths of activation as well as due to the involvement of different neural structures as underlined with statistical analysis. We interpret that our physiological findings demonstrate that different mental strategies are used for correct word recognition in the brains of women and men as assessed with magnetoencephalography (MEG). Our data might be linked to previous findings about the hemispheric asymmetry in male subjects (left lateralized) compared to women in whom both hemispheres seem to be equally involved in word processing.

False recognition depends on depth of prior word processing: a magnetoencephalographic (MEG) study.

Brain activity was measured with a whole head magnetoencephalograph (MEG) during the test phases of word recognition experiments. Healthy young subjects had to discriminate between previously presented and new words. During prior study phases two different levels of word processing were provided according to two different kinds of instructions (shallow and deep encoding). Event-related fields (ERFs) associated with falsely recognized words (false alarms) were found to depend on the depth of processing during the prior study phase. False alarms elicited higher brain activity (as reflected by dipole strength) in case of prior deep encoding as compared to shallow encoding between 300 and 500 ms after stimulus onset at temporal brain areas. Between 500 and 700 ms we found evidence for differences in the involvement of neural structures related to both conditions of false alarms. Furthermore, the number of false alarms was found to depend on depth of processing. Shallow encoding led to a higher number of false alarms than deep encoding. All data are discussed as strong support for the ideas that a certain level of word processing is performed by a distinct set of neural systems and that the same neural systems which encode information are reactivated during the retrieval.

A medial to lateral shift in pre-movement cortical activity in hemi-Parkinson's disease.

OBJECTIVE: Recent evidence suggests that cortical activity associated with voluntary movement is relatively shifted from medial to lateral premotor areas in Parkinson's disease. This shift occurs bilaterally even for unilateral responses. It is not clear whether the shift in processing reflects an overall change in movement strategy, thereby involving alternate cortical areas, or reflects a compensatory change whereby, given the appropriate conditions, less impaired cortical areas are able to provide a similar function in compensation for those areas which are more impaired. This issue was examined in patients with hemi-Parkinson's disease, in whom basal ganglia impairment is most pronounced in one hemisphere. METHODS: Fourteen patients with hemi-Parkinson's disease and 15 age-matched control subjects performed a Go/NoGo finger movement task and the contingent negative variation (CNV) was recorded from 21 scalp positions. RESULTS AND CONCLUSIONS: Maximal CNV amplitudes were found over central medial regions for control subjects, but were shifted more frontally for Parkinson's disease patients, reduced in amplitude over the midline and lateralized towards the side ipsilateral to the greatest basal ganglia impairment. This shift in cortical activity from medial to lateral areas in Parkinson's disease patients appears to reflect a compensatory mechanism operating predominantly on the side of greatest basal ganglia impairment.

Left temporal and temporoparietal brain activity depends on depth of word encoding: a magnetoencephalographic study in healthy young subjects.

Using a 143-channel whole-head magnetoencephalograph (MEG) we recorded the temporal changes of brain activity from 26 healthy young subjects (14 females) related to shallow perceptual and deep semantic word encoding. During subsequent recognition tests, the subjects had to recognize the previously encoded words which were interspersed with new words. The resulting mean memory performances across all subjects clearly mirrored the different levels of encoding. The grand averaged event-related fields (ERFs) associated with perceptual and semantic word encoding differed significantly between 200 and 550 ms after stimulus onset mainly over left superior temporal and left superior parietal sensors. Semantic encoding elicited higher brain activity than perceptual encoding. Source localization procedures revealed that neural populations of the left temporal and temporoparietal brain areas showed different activity strengths across the whole group of subjects depending on depth of word encoding. We suggest that the higher brain activity associated with deep encoding as compared to shallow encoding was due to the involvement of more neural systems during the processing of visually presented words. Deep encoding required more energy than shallow encoding but for all that led to a better memory performance.

Dissociation of motor preparation from memory and attentional processes using movement-related cortical potentials.

The EEG activity preceding self-paced voluntary movements (movement-related cortical potential, MRCP) is smaller if subjects make the same movement each time (regular task) compared with when different movements are made each time (random task). To test whether extra activity in the random task is due to increased motor preparation needed to switch between different movements, or to memory/attentional processes needed to select movements randomly, we compared regular and random movements with an additional alternating task. This alternating task required subjects to make different movements each time as in the random task, but since the task was very simple, the memory/attentional load was similar to that in the regular task. The MRCP was equally large over motor areas in both random and alternating tasks, suggesting that the extra activity over sensorimotor areas reflected processes involved in motor preparation rather than memory/attention. We speculate that, in the regular task, some part of the instructions for the previous movement remains intact, reducing the amount of preparation needed for the next repetition. Thus the MRCP is smaller than in the alternating and random tasks. Although the MRCPs in alternating and random tasks were similar over the motor areas, the random task had more activity than the alternating task in contralateral frontal areas. This part of the MRCP may therefore be related to memory/attentional processes required to randomize the sequence of movements. We conclude that the MRCP contains dissociable components related to motor preparation and memory/attention.

Combining ictal surface-electroencephalography and seizure semiology improves patient lateralization in temporal lobe epilepsy.

PURPOSE: The study goal was to assess the concordance of ictal surface-EEG and seizure semiology data in lateralizing intractable temporal lobe epilepsy (TLE) and to examine the benefits of the combined use of these two methods. METHODS: We independently analyzed the ictal recordings and clinical symptoms associated with 262 seizures recorded in 59 TLE patients. Each seizure was lateralized on the basis of (i) its associated ictal surface-EEG pattern according to a predefined lateralization protocol and (ii) its associated ictal and postictal seizure semiology according to strictly defined clinical criteria. Individual patients were also lateralized based on these data. RESULTS: Ictal surface-EEG findings lateralized 62.6% of seizures and 64.4% of patients. Seizure semiology findings lateralized 46.2% of seizures and 78.0% of patients. There was a high degree of concordance between lateralizations based on these two methods, for both individual seizures and individual patients. Combination of the information from the two methods allowed for lateralization in a greater proportion of both seizures (79.8%) and patients (94.9%). Combined EEG-seizure lateralization was concordant with the side of operation in 33 of 34 patients who underwent successful surgery (Engel's surgical outcome class I/II). CONCLUSIONS: In TLE, there is a high agreement between the lateralization of individual seizures and patients, which is based on ictal surface-EEG findings and seizure semiology. Furthermore, combination of these two methods improves the lateralization of individual seizures and patients. Thus, standardized combined EEG-seizure analysis is a valuable noninvasive tool in the presurgical evaluation of TLE.