Electroencephalography and clinical neurophysiology最新文献

Objectives: We report the analysis of scalp topography and dipole modeling of the rolandic spikes in 6 patients suffering of benign rolandic epilepsy of childhood with extremely high amplitude SEP by tapping stimulation of the finger of the hand.

Methods: EEG and BESA analysis were performed for both rolandic spontaneous interictal spikes and high amplitude scalp activity evoked by tapping and electrical stimulation of the first finger of the right hand.

Results: The evoked responses showed a morphology characterized by a rapid phase (spike) followed by a slow phase (slow wave). The spike presented an early small positive component followed by a main negative component. Similar morphology, dipole configuration and source localization were observed for both rolandic spikes and evoked high amplitude scalp responses. Dipole localization showed an overlap of spatial coordinates between rolandic and evoked spikes.

Conclusions: These findings suggest that the extremely high amplitude SEPs could be evoked spikes which probably had the same cortical generators of the spontaneous rolandic spikes.

Objectives: The present study is aimed at describing electroencephalographic (EEG) changes in the tubercular meningitis (TBM) and correlating these with clinical and radiological findings.

Methods: All the patients underwent a detailed neurological evaluation, CSF analysis, EEG and CT scan studies. Outcome was assessed by the Barthel index (BI) score at the end of 3 months, into good (BI≥12) and poor (BI<12). Thirty-two patients with TBM have been included of which 3 were definite and the remaining highly probable. Their mean age was 28 (range 8–62) years and 8 of whom were females. The majority of these patients were in stage III.

Results: Clinical signs of raised intracranial tension were present in 9 and history of seizure in 11 patients. Cranial CT scan was abnormal in 22 patients. The CT scan abnormalities included hydrocephalus in 20, infarction in 11, exudates in 7 and tuberculoma in 4 patients. The EEG was abnormal in 24 patients. The EEG abnormalities included diffuse theta to delta slowing in 22 patients, intermittent rhythmic delta activity in frontal region in 15, right to left asymmetry in 5 and epileptiform discharges in 4 patients. At the end of 3 months, 5 patients died, 13 had poor, 3 partial and 11 complete recovery. The EEG findings correlated with the severity of meningitis, the degree of coma and outcome at 3 months as assessed by Barthel index score.

Objectives: Instantaneous changes in blood flow velocities during visual stimulation can be assessed by transcranial Doppler sonography (TCD).

Methods: We investigated the possible relationship between the characteristics of photic driving in the EEG elicited by repetitive intermittent photic stimulation and the photoreactive flow changes in the posterior and middle cerebral artery (PCA, MCA) of 25 normal controls and 25 patients with focal epilepsy. Cerebral blood flow velocities (CBFV) of the right PCA (P2 segment) and the left middle cerebral artery (MCA) were measured using a 2 Hz transcranial Doppler device. Simultaneously, scalp EEGs were recorded.

Results: During photic stimulation the mean CBFV increase was 20.4±9.5% in the PCA of the controls (n=132 stimulations) and 16.0±10.8% in epileptic patients (n=150 stimulations, P<0.01). During those stimulation series with a good EEG driving response (n=203), the mean increase of CBFV in the PCA was 19.7±10.0%, as opposed to 14.4±10.5% during the stimulations with a poor EEG response (n=79, P<0.01). A good photic driving response was associated with a higher increase of CBFV in the PCA than a poor one. The increase in CBFV of the PCA in normal controls was higher than in patients with focal epilepsy.

Conclusions: This may indicate that epileptic patients have a reduced coupling between neuronal activation and blood flow.

The silent period (SP) following transcranial magnetic stimulation (TMS) of the motor cortex is mainly due to cortical inhibitory mechanisms. The aim of the present study was to investigate these inhibitory phenomena in primary motor cortex epilepsy. We studied the TMS-induced SP in both the first dorsal interosseous (FDI) muscles in 8 patients who suffered from cryptogenic partial epilepsy with seizures starting with clonic movements of the right upper limb. All patients were on chronic medication with antiepileptic drugs. Therefore, besides contrasting the results with 16 age-matched normal controls, we also studied 10 patients receiving similar antiepileptic treatments who suffered from cryptogenic partial epilepsy with seizures characterised by the absence of clonic manifestations. The duration of the SP was bilaterally increased in the patients with clonic seizures when compared with the two other groups of subjects. The SP was longer in the left FDI muscle (contralateral to the side of the clonic manifestation in all the patients). Our findings likely indicate enhanced interictal inhibitory mechanisms in patients with partial epilepsy involving the primary motor cortex. The resulting inhibitory effect could be greater in the intact hemisphere rather than in the affected one, in which the hyperexcitability of the epileptic focus had to be counterbalanced.

Objective: A previously described seizure detection algorithm (CNET) (Gabor, A.J., Leach, R.R. and Dowla, F.U. Automated seizure detection using a self-organizing neural network. Electroenceph. clin. Neurophysiol., 1996, 99: 257–266) was validated with 200 records from 65 patients (4553.8 h of recording) containing 181 seizures. Design and methods: Performance of the algorithm was manifest by its sensitivity ((seizures detected/total seizures)×100) and selectivity (false-positive errors/Hr-FPH). Comparisons with the Monitor detection algorithm (Version 8.0c, Stellate Systems) and audio-transformation (Oxford Medilog) were performed. Results: CNET detected 92.8% of the seizures and had a mean FPH of 1.35±1.35. Monitor detected 74.4% of the seizures and had a mean FPH of 3.02±2.78. Audiotransformation detected all but 3 (98.3%) of the seizures. Selectivity for this detection strategy was not defined. Conclusions: This study not only validates the CNET algorithm, but also the notion that seizures have frequency-amplitude features that are localized in signal space and can be selectively identified as being distinct from other types of EEG patterns. The ear is a specialized frequency-amplitude detector and when the signal is transformed into audio frequency range (audio-transformation), seizures can be detected with better sensitivity as compared to the other strategies examined.

Subdural electrodes made of stainless steel, which were believed to be unsuitable for recording slow potentials, can still record Bereitschaftspotential (BP) (Neshige, R., Lüders, H. and Shibasaki, H. Recording of movement-related potentials from scalp and cortex in man. Brain, 1988, 11: 719–736) and ictal direct current (DC) shifts (Ikeda, A., Terada, K., Mikuni, N., Burgess, R.C., Comair, Y., Taki, W., Hamano, T., Kimura, J., Lüders, H.O. and Shibasaki, H. Subdural recording of ictal DC shifts in neocortical seizures in humans. Epilepsia, 1996b, 37: 662–674) sufficiently. In this study, therefore, the effects of different kinds of metals on slow potential recordings were reevaluated. First, slow electro-oculograms (EOGs) were recorded with 3 different levels of input impedance (200 MΩ, 470 kΩ and 10 kΩ) of a DC amplifier by using surface electrodes made of silver (Ag), silver/silver chloride (Ag/AgCl) and stainless steel. Secondly, BP was recorded by using the above electrodes with a long time constant of 3 s and with a fixed input impedance of 100 MΩ. As a result: (1) slow EOGs were equally recorded with the input impedance of 200 MΩ and 470 kΩ regardless of the kind of metals used, although stainless steel electrodes caused baseline fluctuation, (2) low input impedance of 10 kΩ allowed only the Ag/AgCl electrode to record slow EOGs without any decay, and (3) electrodes made of stainless steel could record BP as efficiently as the other two types of electrode with high input impedance. In conclusion, electrodes with a large surface area contact such as cup electrodes and an amplifier with a large input impedance, electrodes made of Ag, and even of stainless steel, can record slow potentials reasonably well.

To assist in the reviewing of prolonged EEGs, we have developed an automatic EEG analysis method that can be used to compress the prolonged EEG into two pages. The proposed approach of Automatic Analysis of Segmented-EEG (AAS-EEG) consists of 4 basic steps: (1) segmentation; (2) feature extraction; (3) classification; and (4) presentation. The idea is to break down the EEG into stationary segments and extract features that can be used to classify the segments into groups of like patterns. The final step involves the presentation of the processed data in a compressed form. This is done by providing the EEGer with a representative sample from each group of EEG patterns and a compressed time profile of the complete EEG. To verify the above approach, 41 6 h EEG records were assessed for normality via the AAS-EEG and conventional EEG approaches. The difference between the overall assessment via compressed and conventional EEG was within one abnormality level 100% of the time, and within one-half level for 73.6% of the records. We demonstrated the feasibility and reliability of automatically segmenting and clustering the EEG, thus allowing the reduction of a 6 h tracing to a few representative segments and their time sequence. This should facilitate review of long recordings during monitoring in the ICU.