Sensations and reaction times evoked by electrical sinusoidal stimulation.

OBJECTIVE: To determine whether 5 Hz and 2000 Hz sinusoidal electric currents evoke different sensations and to indirectly evaluate which peripheral nerve fibers are stimulated by these different frequencies. METHODS: One hundred and fifty subjects chose three among eight descriptors of sensations evoked by 5 Hz and 2000 Hz currents and the results were submitted to factor analysis. In 20 subjects, reaction times to 5, 250 and 2000 Hz currents were determined at 1.1 x ST and reaction times to 5 Hz currents were also determined at 2 x ST. RESULTS: Responses were grouped in four factors: Factor 1, which loaded mainly in descriptors related to tweezers stimulation, was higher than the other factors during 2000 Hz stimulation at 1.5 x ST. Factor 2, which loaded mainly in descriptors related to needle stimulation, was higher than the other factors during 5 Hz stimulation. Factor 1 increased and Factor 2 decreased with an increase in 5 Hz intensity from 1.5 to 4x ST. Reaction times measured from the fastest responses were significantly different: 0.57 s (0.16 to 1.60), 0.34 s (0.12 to 0.71) and 0.22s (0.08 to 0.35) for 5, 250 and 2000 Hz, respectively, and 0.22s (0.11 to 0.34) for 5 Hz at 2 x ST. CONCLUSIONS: Sinusoidal electrical stimulation of 5 Hz and 2000 Hz evoke different sensations. At juxta-threshold intensities, RT measurements suggest that 2000 Hz stimulates Abeta-fibers, 250 Hz Abeta- or A partial differential-fibers, 5 Hz Abeta-, A partial differential- or C-fibers. The fiber type, which was initially stimulated by the lower frequencies, depended on inter-individual differences.

Complete remission of epileptic psychosis after temporal lobectomy: case report.

We report a case of a female patient with refractory complex partial seizures since 15 years of age, recurrent postictal psychotic episodes since 35 which evolved to a chronic refractory interictal psychosis and MRI with right mesial temporal sclerosis (MTS). After a comprehensive investigation (video-EEG intensive monitoring, interictal and ictal SPECT, and a neuropsychological evaluation including WADA test) she was submitted to a right temporal lobectomy. Since then, she has been seizure-free with remission of psychosis, although with some persistence of personality traits (hiperreligiosity, viscosity) which had been present before surgery. This case supports the idea that temporal lobectomy can be a safe and effective therapeutic measure for patients with MTS, refractory epilepsy and recurrent postictal epileptic psychosis or interictal epileptic psychosis with postictal exacerbation.

Secondary bilateral synchrony due to fronto-mesial lesions. An invasive recording study.

Frontal lobe epilepsies may present difficulties in focus localization in the pre-operative work-up for epilepsy surgery. This is specially true in patients with normal MRIs. We report on a 16 years-old girl that started with seizures by the age of 8 years. They were brief nocturnal episodes with automatisms such as bicycling and boxing. Seizure frequency ranged from 4-10 per night. Scalp EEG showed few right frontal convexity spiking and intense secondary bilateral synchrony (SBS). High resolution MRI directed to the frontal lobes was normal. Ictal SPECT suggested a right fronto-lateral focus. Ictal video-EEG showed no focal onset. She was submitted to invasive recordings after subdural plates implantation. Electrodes covered all the frontal convexity and mesial surface bilaterally. Ictal recordings disclosed stereotyped seizures starting from the right mesial frontal. Using a high-resolution tool to measure intra and interhemispheric latencies, the timing and direction of seizure spread from the right fronto-mesial region were studied. Motor strip mapping was performed by means of electrical stimulation. She was submitted to a right frontal lobe resection, 1.5 cm ahead of the motor strip and has been seizure free since surgery (8 months). Pathological examination found a 4 mm area of cortical dysplasia. Invasive studies are needed to allow adequate localization in patients with non-localizatory non-invasive work-up and may lead to excellent results in relation to seizures after surgery.

Monoamines and their metabolites in cerebrospinal fluid and temporal cortex of epileptic patients.

The involvement of monoamines in the initiation or maintenance of epileptic phenomena has been extensively studied in cerebral tissues and in cerebrospinal fluid. The present work was undertaken to study monoamines and their metabolites in human spiking and non-spiking temporal cortex excised from patients with complex partial seizures unresponsive to available anticonvulsants. The same substances were also analyzed by HPLC-ED in cerebrospinal fluid obtained 24 h before the surgical procedure and compared with those from patients with chronic headache and normal neurological evaluation. The results show increased 5-HT, 5-HIAA and HVA levels in spiking compared with non-spiking cortex. Cerebrospinal fluid levels of 5-HIAA and HVA are concomitantly increased in epileptic compared with headache patients.

Surgical treatment of refractory epilepsy associated with space occupying lesions. Experience and review.

Surgery for space occupying lesions of the brain associated with intractable epilepsy represents a special problem because relief of the epilepsy in as much an operative goal as excision of the space occupying lesion itself. This study concerns 32 patients with space occupying lesions and intractable epilepsy who underwent excision of the lesion with acute intraoperative electrocorticography guided resection of the epileptogenic focus. Of the 32 patients, 16 formed a subgroup of gangliogliomas alone. The remaining were mixed lesions, predominantly benign. The duration of seizures in these patients ranged from 2 to 30 years, and the seizure frequency varied from 1 to 300 convulsions per month. The operative procedures included temporal corticectomy, amygdalo-hippocampectomy, and extratemporal corticectomies. Twenty nine patients were in Engel class I postoperatively, and three patients were in Engel class II. The findings with gangliogliomas were also considered in a separate group. This study strongly suggests that the operative procedure under electrocorticography guidance improves seizure outcome in space occupying lesions related intractable epilepsy.

Surgical approaches to tumors and epileptogenic zones close to Wernicke's area.

Surgical procedures near to language related brain regions may cause severe morbidity in relation to speech. Operations performed under local anesthesia and intraoperative cortical mapping may minimize these risks. Six patients with tumors near the Wernicke's area were treated (2 low-grade astrocytomas, 1 ganglioglioma, 1 xanthoastrocytoma, 1 metastasis, 1 glioblastoma). Their clinical presentation consisted of epilepsy (n = 4) and dysphasia (n = 2). The skin and periosteum were infiltrated with local anesthetic and an ample craniotomy was performed. Cortical stimulation with an unipolar electrode was then carried out with concomitant speech testing (mainly comprehension and sequential speech). After mapping, the best surgical approach aiming to avoid the mapped area was elected. In 5 cases the resection was total and in 1, partial (glioblastoma). There was a transitory (10 days) worsening of the pre-operative deficit in 1 case (glioblastoma). In 3 patients, the speech areas were displaced: posteriorly (n = 2) or anteriorly (n = 1). Surgical procedures under local anesthesia are safe and may avoid post-operative language disturbances in patients with tumors near to Wernicke's area.

Results from the intracarotid amytal procedure in patients with uni or bitemporal lobe epilepsy and mesial sclerosis.

This study discusses the results from the IAP and its lateralizing and prognostic value in patients with temporal lobe epilepsy (TLE) and mesial temporal sclerosis (MTS). Eighteen patients were submitted to the IAP. Fifteen had bitemporal and 3 unitemporal lobe epilepsies. All patients had MTS on MRI and in one there was an unrelated lesion in the contralateral hippocampus. Nine bitemporal patients passed after the injection ipsilateral to the MTS and 4 failed bilaterally. One bitemporal passed bilaterally. Seven of these bitemporal patients passed an injection ipsilateral to MTS and failed on contralateral injection. Two of the unitemporal lobe patients passed the ipsilateral injection and failed the contralateral one. One of the unitemporal lobe patients failed bilaterally the IAP. Overall, 56% of the group disclosed the pass ipsi-/fail contralateral pattern in the IAP. Eight patients were operated, are seizure free and had no additional memory deficit. Many patients with TLE were found to have the pass ipsi-/fail contralateral pattern in the IAP. This might prove to be of lateralizing and prognostic value in such cases.

Recomendaçöes referentes ao registro clínico digital do EEG / Recommendations of Digital Clinical Recording (EEG)

Até recentemente o registro do EEG convencional era feito quase exclusivamente em papel, com a análise sendo executada visualmente. Considerando apenas a gravaçäo (aquisiçä) do EEG, pode-se atualmente dividi-la de forma arbitrária em: 1) sistemas convencionais de registro de EEG em papel; 2) sistemas híbridos com registro em papel e a presença de processadores, porém sem registro digital; os processadores podem permitir, por exemplo, a alteraçäo de programas; 3) sistemas do tipo "paperless" näo digital, com registro através de sistema de modulaçäo em "tape"; 4) sistemas de registro digital do EEG (DEEG). A análise do EEG continua sendo feita da forma visual clássica, porém o registro digital permite também executar diferentes tipos de processamento do sinal do DEEG. Estas recomendaçöes, envolvendo apenas aspectos referentes ao registro clínico digital do EEG, representam o trabalho de uma comissäo organizada pelo departamento de mapeamento topográfico da SBNC e visam näo somente delinear requisitos mínimos como também comentá-los do ponto de vista didático

[Related observations for the use of mounting between neck posterior and scalp in evoked potentials by median nerve stimulation]. / Observações relacionadas à utilização de montagens entre a face posterior do pescoço e o couro cabeludo no potencial evocado por estimulação do nervo mediano.

Somatosensory evoked potentials after stimulation of the median nerve were obtained in a group of normal individuals. The components obtained between 12 and 22 ms were analysed with cephalic and non-cephalic references. It is shown that the P13-14 complex is the major contributor for the amplitude of the N13 component recorded with electrodes between the posterior neck and the scalp. It has not been possible to detect differences in amplitude or latencies for the components N18 and P22 recorded between FZ-non cephalic and C6-FZ. Implications of these findings to clinical interpretations of the responses are discussed.

Observaçöes relacionadas à utilizaçäo de montagens entre a face posterior do pescoço e o couro cabeludo no potencial evocado por estimulaçäo do nervo mediano / Related observations for the use of mounting between neck posterior and scalp in evoked potentials by median nerve stimulation

Foram realizados potenciais evocados por estimulaçäo do nervo mediano no punho, em grupo de voluntários normais. Foram avaliados os componentes que ocorreram entre 12 e 22 ms. Os registros foram feitos com referências cefálicas e näo cefálicas. Foi evidenciada maior contribuiçäo do complexo P13-14 na amplitude do componente N13 registrado entre C6 e Fz. Näo foram detectadas diferenças significativas na amplitude e latência dos componentes N18 e P22 quando avaliados nas montagens FZ-näo cefálico e C6-FZ. Säo discutidas as implicaçöes desses achados para a interpretaçäo clínica dessas respostas