The recently described slow oscillations of amplitude of theta and alpha waves of the EEG (with a frequency below 0.08 Hz) in healthy subjects are attributed to the autonomic nervous system with control at the brain stem level. In the present pilot study, the slow brain rhythms were analyzed in a patient with Alzheimer’s disease and were compared to a healthy subject. Dynamic analysis of the EEG was performed using time-frequency mapping which gives simultaneous time and frequency representation of the brain signal. This method comprises a transform of the filtered EEG signal into its analytic form and application of the Wigner distribution modified by time and frequency smoothing. It has been shown that the envelope of both theta and alpha activities oscillates at 0.04 Hz and 0.07 Hz in the healthy subject and at 0.03 Hz and 0.06 Hz in a patient with Alzheimer’s disease. The amplitude of the slow oscillations of theta activity was substantially higher in the patient with Alzheimer’s disease as compared with the healthy subject. It is being proposed that the increase of slow brain rhythms in the patient with Alzheimer’s disease reflects an abnormal activity of the autonomic nervous system. However, the underlying pathophysiological mechanisms need to be further studied.
Effect of phénobarbital (PhB, 20 and/or 40 mg/kg) on epileptic ECoG phenomena induced by metrazol was studied in acute experiments in rats aged 7, 12, 18, 25 and 90 days. Fractionated administration of metrazol (20 mg/kg i.p. each 300 s) was used to quantify the effects of PhB. First signs of metrazol action (sharp elements and/or rhythmic metrazol activity) were not reliably influenced by PhB. On the contrary, the latency of the first EEG seizures as well as of the first generalized EEG seizures was prolonged and thus a dose necessary for their elicitation was increased in all age groups. These differences reached statistical significance in 12-, 18- and 25-day-old rats. A lack of effect of PhB against the rhythmic metrazol activity supports the adequacy of this activity as a model of human absences. Differences between the development of antiepileptic and hypnotic effects of PhB (described earlier) suggest two different mechanisms of action.
The paper examines sources of brain activity, contributing to EEG patterns which correspond to motor imagery during training to control brain-computer interface. To identify individual source contribution into electroencephalogram recorded during the training Independent Component Analysis was used. Then those independent components for which the BCI system classification accuracy was at maximum were treated as relevant to performing the motor imagery tasks, since they demonstrated well exposed event related de-synchronization and event related synchronization of the sensorimotor μ-rhythm during imagining of contra- and ipsilateral hand movements. To reveal neurophysiological nature of these components we have solved the inverse EEG problem to locate the sources of brain activity causing these components to appear in EEG. The sources were located in hand representation areas of the primary sensorimotor cortex. Their positions practically coincide with the regions of brain activity during the motor imagination obtained in fMRI study. Individual geometry of brain and its covers provided by anatomical MR images was taken into account when localizing the sources.
The new method is based on non-linear one-step predictor, which is designed as MLP neural network. It is a kind of low-pass non-linear filter. The difference between raw EEG and the ANN output is then a subject of band spectral analysis. The differences in this power spectrum between Alzheimer's diseased and control patient group are statistically significant.
Epileptic afterdischarges induced by electrical stimulation of the sensorimotor cortex as well as minimal metrazol seizures are characterized by EEG spike-and-wave rhythm and nearly the same motor pattern of clonic seizures. The action of ethosuximide on these two models was tested in adult rats with implanted electrodes. Cortical afterdischarges remained practically uninfluenced by ethosuximide (62.5 or 125 mg/kg i.p.) whereas minimal metrazol seizures were suppressed in a dose-dependent manner (doses of 31.25, 62.5 and 125 mg/kg i.p. were used). Present results in connection with recent data on the abolition of spike-and-wave rhythm elicited by low systemic doses of pentylenetetrazol suggest that spike-and-wave rhythm does not represent a single entity.
There is growing interest to analyze electroencephalogram (EEG) signals with the objective of classifying schizophrenic patients from the control subjects. In this study, EEG signals of 15 schizophrenic patients and 19 age-matched control subjects are recorded using twenty surface electrodes. After the preprocessing phase, several features including autoregressive (AR) model coefficients, band power and fractal dimension were extracted from their recorded signals. Three classifiers including Linear Discriminant Analysis (LDA), Multi-LDA (MLDA) and Adaptive Boosting (Adaboost) were implemented to classify the EEG features of schizophrenic and normal subjects. Leave-one (participant)-out cross validation is performed in the training phase and finally in the test phase; the results of applying the LDA, MLDA and Adaboost respectively provided 78%, 81% and 82% classification accuracies between the two groups. For further improvement, Genetic Programming (GP) is employed to select more informative features and remove the redundant ones. After applying GP on the feature vectors, the results are remarkably improved so that the classification rate of the two groups with LDA, MLDA and Adaboost classifiers yielded 82%, 84% and 93% accuracies, respectively.
In the present study, we investigated the effects of vagus nerve stimulation (VNS), a proposed treatment for patients with intractable epilepsy, on cardiac rhythm following seizures induced by pentylenetetrazole (PTZ) in Wistar rats. After a baselinerecording of electroencephalogram (EEG), electrocardiogram (ECG) and blood pressure (BP), rats in the first group received a single convulsive dose of PTZ (70 mg/kg) (Group 1). In the other
two groups, the Wistar rats were implanted with a cuff electrode on the left cervical vagus nerve. One day after surgery, rats in the second group were treated with VNS (Group 2), whereas rats in the third group were connected to the stimulator but did not receive VNS (Group 3). Ten minutes after VNS onset, 70 mg/kg dose of PTZ was injected. EEG, ECG and BP were continuously recorded during post-injection period. Seizure severity was scored behaviorally. Then, baseline, ictal and postictal periods were analyzed for cardiac rhythms, seizure severity and blood pressure variability. PTZ treatment induced tonic-clonic seizure activity in all animals of Group 1 and Group 3. In these groups a marked increase of mean arterial blood pressure (MABP) but a significant decrease in heart rate and PP interval fluctuations was observed at postictal period. However, in the VNS-treated group the seizure scores and cardiac parameter returned to the baseline level. Present results emphasize that VNS effectively reduces seizure severity and suppress the seizure-induced cardiac rhythm changes.