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E Urrestarazu

Publications and source records attributed to E Urrestarazu.

14 recordsLinked to original sources
PubMed2006

High-frequency oscillations during human focal seizures.

Discrete high-frequency oscillations (HFOs) in the range of 100-500 Hz have previously been recorded in human epileptic brains using depth microelectrodes. We describe for the first time similar oscillations in a cohort of unselected focal epileptic patients implanted with EEG macroelectrodes. Spectral analysis and visual inspection techniques were used to study seizures from 10 consecutive patients undergoing pre-surgical evaluation for medically refractory focal epilepsy. Four of these patients had focal seizure onset in the mesial temporal lobe, and in all 12 of their seizures, well-localized, segmental, very high frequency band (VHF: 250-500 Hz) oscillations were visually identified near the time of seizure onset from contacts in this zone. Increased high-frequency band (HF: 100-200 Hz) activity compared with the background was distinguished both visually and with spectral analysis later in the seizures of 3/4 mesial temporal patients, involving contacts in the generator region and, in one patient, areas of contralateral peri-hippocampal propagation. Three patients with well-defined neocortical seizure-onset areas also demonstrated focal HF or VHF oscillations confined to the seizure-onset channels during their eight seizures. No discrete HF or VHF activity was present in the poorly localized seizures from the remaining three patients. These results show that discrete HFOs can be recorded from human focal epileptic brain using depth macroelectrodes, and that they occur mostly in regions of primary epileptogenesis and rarely in regions of secondary spread. Absent high-frequency activity seems to indicate poor localization, whereas the presence of focal HFOs near the time of seizure onset may signify proximity to the epileptogenic focus in mesial temporal lobe and neocortical seizures. We postulate that focal HFOs recorded with depth macroelectrodes reflect the partial synchronization of very local oscillations such as those previously studied using microelectrodes, and result from interconnected small neuronal ensembles. Our finding that localized HFOs occur in varying anatomical structures and pathological conditions perhaps indicates commonality to diverse epileptogenic aetiologies.

Adult↗
PubMed2006

Independent component analysis identifies ictal bitemporal activity in intracranial recordings at the time of unilateral discharges.

OBJECTIVE: To apply independent component analysis (ICA) in intracranial recordings to analyze interactions during temporal lobe seizures. METHODS: Seizures from 20 patients with bitemporal implantation were classified as unilateral or bilateral and analyzed with ICA. During the period preceding bilateral activity, correlation coefficients were calculated between ICA components having ictal activity during the unilateral seizure phase (early ICA components) and every channel of the original EEG. ICA components were classified as unilateral if the correlation was >0.2 exclusively with channels in one hemisphere; and bilateral if both hemispheres were involved. RESULTS: One hundred twenty-three seizures were analyzed. Thirty-two percent of visually classified unilateral seizures and 64% of bilateral seizures (during the unilateral phase) had bilateral ICA components. The proportion of early ICA components that were bilateral and the proportion of channels contralateral to the visually identified seizure with correlation higher than 0.2 with at least one early ICA component were significantly lower in seizures that stayed unilateral than in seizures that later became bilateral by visual inspection (11 and 10%, respectively, in unilateral seizures; 33 and 28% in bilateral seizures; P=0.001). CONCLUSIONS: In patients with bitemporal epilepsy, approximately 20% of the components extracted using ICA have a bitemporal distribution even at the time when the seizures are apparently unilateral. The presence of early contralateral ictal activity is more frequent and extensive in seizures that later become evidently bilateral. SIGNIFICANCE: Minimal contralateral seizure activity is present even when the discharge appears unilateral and this is more frequent in seizures which later spread to the contralateral temporal lobe.

Adult↗
PubMed2006

A system for automatic artifact removal in ictal scalp EEG based on independent component analysis and Bayesian classification.

OBJECTIVE: To devise an automated system to remove artifacts from ictal scalp EEG, using independent component analysis (ICA). METHODS: A Bayesian classifier was used to determine the probability that 2s epochs of seizure segments decomposed by ICA represented EEG activity, as opposed to artifact. The classifier was trained using numerous statistical, spectral, and spatial features. The system's performance was then assessed using separate validation data. RESULTS: The classifier identified epochs representing EEG activity in the validation dataset with a sensitivity of 82.4% and a specificity of 83.3%. An ICA component was considered to represent EEG activity if the sum of the probabilities that its epochs represented EEG exceeded a threshold predetermined using the training data. Otherwise, the component represented artifact. Using this threshold on the validation set, the identification of EEG components was performed with a sensitivity of 87.6% and a specificity of 70.2%. Most misclassified components were a mixture of EEG and artifactual activity. CONCLUSIONS: The automated system successfully rejected a good proportion of artifactual components extracted by ICA, while preserving almost all EEG components. The misclassification rate was comparable to the variability observed in human classification. SIGNIFICANCE: Current ICA methods of artifact removal require a tedious visual classification of the components. The proposed system automates this process and removes simultaneously multiple types of artifacts.

Algorithms↗
PubMed2004

Potentials evoked by chirp-modulated tones: a new technique to evaluate oscillatory activity in the auditory pathway.

OBJECTIVE: Steady-state potentials are oscillatory responses generated by a rhythmic stimulation of a sensory pathway. The frequency of the response, which follows the frequency of stimulation, is maximal at a stimulus rate of 40 Hz for auditory stimuli. The exact cause of these maximal responses is not known, although some authors have suggested that they might be related to the 'working frequency' of the auditory cortex. Testing of the responses to different frequencies of stimulation may be lengthy if a single frequency is studied at a time. Our aim was to develop a fast technique to explore the oscillatory response to auditory stimuli, using a tone modulated in amplitude by a sinusoid whose frequency increases linearly in frequency ('chirp') from 1 to 120 Hz. METHODS: Time-frequency transforms were used for the analysis of the evoked responses in 10 subjects. Also, we analyzed whether the peaks in these responses were due to increases of amplitude or to phase-locking phenomena, using single-sweep time-frequency transforms and inter-trial phase analysis. RESULTS: The pattern observed in the time-frequency transform of the chirp-evoked potential was very similar in all subjects: a diagonal band of energy was observed, corresponding to the frequency of modulation at each time instant. Two components were present in the band, one around 45 Hz (30-60 Hz) and a smaller one between 80 and 120 Hz. Inter-trial phase analysis showed that these components were mainly due to phase locking phenomena. CONCLUSIONS: A simultaneous testing of the amplitude-modulation-following oscillatory responses to auditory stimulation is feasible using a tone modulated in amplitude at increasing frequencies. The maximal energies found at stimulation frequencies around 40 Hz are probably due to increased phase-locking of the individual responses.

Acoustic Stimulation↗
PubMed2002

[Lamotrigine in the adult-onset epilepsy: efficacy and long-term safety].

BACKGROUND: LTG is a new antiepileptic drug that is nowadays very often used in epileptic patients. OBJECTIVES: To determine efficacy and safety of Lamotrigine (LTG) in the first five years after its marketing in patients at a third level university hospital, as well as its impact on the management of classic antiepileptic drugs (AED). PATIENTS AND METHOD: We reviewed retrospectively our Epilepsy Unit Database. One hundred patients were treated with LTG in a 5-year period. Efficacy was evaluated comparing seizure frequency in a 6-month period before and after LTG. The type of epilepsy, side effects, blood levels and concomitant treatments were considered in the analysis. RESULTS: LTG was effective in all groups of epileptic patients studied. Eighteen percent of patients became seizure-free. Seventeen percent of patients improved more than 50%. Fifty-seven percent of patients remained treated with LTG after four years of follow-up. Side effects were mild, but frequent; only four patients discontinued LTG because of adverse effects. Serum levels were usually high, but showed no relation with clinical efficacy. The mean number of AED taken per patient increased. CONCLUSIONS: LTG is a safe an effective drug in epilepsy. It has a clear impact in the management of the epileptic patients.

Adolescent↗
PubMedDate not supplied

[Overall treatment of vascular epilepsy].

Cerebrovascular disease has different acute, ischemic and hemorrhagic presentations and may be associated with epileptic crises during the acute phase, or a later epileptic syndrome may develop. Status epilepticus is an infrequent complication which may appear at any time during the course of the illness, sometimes as the first and only sign of epilepsy. The risk of acute crises or of an epileptic syndrome varies depending on the nature of the vascular accident: its occurrence is more likely in hemorrhagic lesions and in those involving the cerebral cortex. The acute crises may be treated with benzodiazepines or with fast acting antiepileptic drugs; parenteral administration may sometimes be necessary. The need for prolonged prophylactic antiepileptic treatment is still under discussion, since there is no evidence that this prevents later development of an epileptic syndrome. The management of status epilepticus is the same whatever the etiology, although one has to take account of the risk of side-effects related to the age and general health of the patient. When deciding on treatment for vascular epilepsy consideration should be given not only to which drugs are to be used, but also their pharmacokinetic characteristics and interactions with any treatment required by the patient for coexisting conditions such as arterial hypertension, heart failure, anticoagulation, diabetes, etc.

Acute Disease↗
PubMedDate not supplied

[Vagal stimulation in the treatment of epilepsy].

INTRODUCTION: The vagal nerve stimulation is a new technique for the treatment of drug resistant epilepsies. DEVELOPMENT: In 1997, it was approved in United States by the FDA to be used in adults with refractory focal epilepsies not candidates for epilepsy surgery. Its mechanism of action is unknown. The results in the controlled studies indicated a decrease of 30 50% in the seizure frequency in around 50% of the patients. Although more experience is needed to corroborate these results, it seems reasonable as a treatment for patients with difficult epilepsies, especially when the response to the antiepileptic drugs is poor or they are producing secondary effects, and the resection of the focus is not possible.

Adolescent↗
PubMedDate not supplied

[Postictal paralysis during video-EEG monitoring studies].

OBJECTIVE: To know the frequency of Todd s paralysis during the video EEG monitoring studies, to investigate in its pathophysiology, and to confirm its value to localise the epileptic focus. PATIENTS AND METHODS: We reviewed 114 monitoring studies, in 102 patients. RESULTS: Sixty patients had epileptic seizures. An obvious paresis was noted in four seizures of two patients (3 and 1, respectively). Both patients had frontal epilepsy. During the paralysis, in the first patient the EEG showed ictal discharges on the contralateral centrotemporal area. In the second patient, the EEG demonstrated slow waves in the contralateral frontal region. The ictal onset was contralateral to the paresis in all cases. No patient with pseudoseizures had paralysis. CONCLUSIONS: Postconvulsive paralysis are not frequent in video EEG monitoring studies. However, if present it points out to a contralateral seizure onset. In our series it happened in patients with frontal seizures. The EEG may help to clarify if it correspond to a true postictal phenomenon or to a ictal paralysis.

Adult↗
PubMedDate not supplied

[Ictal asystolia in the differential diagnosis of dizziness].

Frequently, epileptic seizures are accompanied by changes in the heart rate. They are usually transient and irrelevant for the patient's symptoms and the patient recorders his usually baseline rhythm in second or a few minutes. In this report we present a case of a patient diagnosed previously of epilepsy who presented episodes of dizziness and presyncope. During the video-EEG study we recorded one of these spells. The diagnosis of this spell was a focal seizure associated with asystole: the seizure was almost asymptomatic, and only when the asystole developed (40 seconds after the EEG ictal changes) the patient complained about dizziness. Recovery was fast, but treatment with pacemaker must be considered.

Diagnosis, Differential↗
PubMedDate not supplied

[Independent Components Analysis (ICA) in the study of electroencephalographic signals].

Independent Component Analysis (ICA) is a mathematical tool able to separate complex signals in statistically independent components. It solves the blind source separation problem (BSS). The EEG satisfies most of the assumptions of ICA, so it may be an adequate signal for ICA for its use. In this paper we review the method and the applications of ICA in EEG. The studied applications are: a) artifacts removal; b) source estimation of spikes; c) analysis of seizures. Several studies have demonstrated that ICA is useful to remove artifacts from contaminated EEG records without distorting cerebral activity. It is able to decompose epileptic discharges and seizures in independent spatio-temporal components. In combination with techniques of source localisation, as dipole modelling, ICA improves the localization of the epileptic focus. Finally, we discuss the future role of ICA in the study of epileptic patients.

Algorithms↗
PubMedDate not supplied

[Mathematical analyses in the study of electroencephalographic signals].

AIM: The principal mathematical techniques applied to the EEG are reviewed. DEVELOPMENT: After the introduction of digital EEG, new mathematical tools have been developed for the EEG analysis. Nowadays there are several techniques that analyse the EEG signal in different ways, getting a better understanding of the EEG: development of new montages; artifact removal; analysis in time domain, phase coherence and synchrony; source analysis; epileptic seizures detection and prediction; superposition of electrical activity and other neuroimaging techniques. Although they have demonstrated their efficacy, the comparison between them is not always easy. CONCLUSIONS: The development of mathematical tools for EEG analysis has improved the knowledge of the electric cerebral activity in normal and pathological conditions. They study many different aspects of the EEG signal. Their continuous development will produce an increase the knowledge of the normal and pathological cerebral functions.

Diagnosis, Computer-Assisted↗