RESUMO
OBJECTIVE: To investigate the P18 component in the posterior to anterior neck montage after median nerve stimulation. METHODS: Somatosensory evoked potentials, through electrical wrist stimulation, were collected. In 12 subjects, the presence of the P18 component was evaluated in the posterior to anterior neck montage. In 10 subjects, the effects of simultaneous vibration of the hand were evaluated. In five subjects, responses after double-pulse stimulation (ISI 20 ms) were evaluated. RESULTS: The P18 component was identified in all subjects. Vibration reduced the amplitude of all components except the P18 and N18. Double-pulse stimulation reduced the amplitude of the P18 and the N18 components without significantly changing the amplitude of the other components. CONCLUSIONS: The posterior to anterior neck montage allows for recording the P18 component. The amplitude reduction of all components during vibration, except N18 and P18, is interpreted as reflecting inhibitory activities at the cuneiform nucleus and at the segmental dorsal horn of the spinal cord, respectively. The reduction in the P18 component after double-pulse stimulation is compatible with previous observations on the positive component of cord dorsum potentials. SIGNIFICANCE: Studying this component may add to the knowledge of the function of the spinal cord in humans.
Assuntos
Potenciais Somatossensoriais Evocados/fisiologia , Nervo Mediano/fisiologia , Córtex Somatossensorial/fisiologia , Adulto , Estimulação Elétrica , Eletroencefalografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Tempo de Reação/fisiologia , Medula Espinal/fisiologiaRESUMO
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.
Assuntos
Estimulação Elétrica/métodos , Fibras Nervosas Mielinizadas/fisiologia , Fibras Nervosas Amielínicas/fisiologia , Tempo de Reação , Tato/fisiologia , Adolescente , Adulto , Estimulação Elétrica/efeitos adversos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Dor/etiologia , Dor/fisiopatologia , Parestesia/etiologia , Parestesia/fisiopatologia , Pressão , Valores de Referência , Limiar Sensorial , Vibração , Adulto JovemRESUMO
OBJECTIVE: To evaluate the effects of an acute dose of the benzodiazepine (BZ) lorazepam in young healthy volunteers on five distinguishable visual perception abilities determined by previous factor-analytic studies. METHODS: This was a double-blind, cross-over design study of acute oral doses of lorazepam (2 mg) and placebo in young healthy volunteers. We focused on a set of paper-and-pencil tests of visual perceptual abilities that load on five correlated but distinguishable factors (Spatial Visualization, Spatial Relations, Perceptual Speed, Closure Speed, and Closure Flexibility). Some other tests (DSST, immediate and delayed recall of prose; measures of subjective mood alterations) were used to control for the classic BZ-induced effects. RESULTS: Lorazepam impaired performance in the DSST and delayed recall of prose, increased subjective sedation and impaired tasks of all abilities except Spatial Visualization and Closure Speed. Only impairment in Perceptual Speed (Identical Pictures task) and delayed recall of prose were not explained by sedation. CONCLUSION: Acute administration of lorazepam, in a dose that impaired episodic memory, selectively affected different visual perceptual abilities before and after controlling for sedation. Central executive demands and sedation did not account for results, so impairment in the Identical Pictures task may be attributed to lorazepam's visual processing alterations.
Assuntos
Hipnóticos e Sedativos/farmacologia , Lorazepam/farmacologia , Percepção Visual/efeitos dos fármacos , Adolescente , Adulto , Cognição/efeitos dos fármacos , Estudos Cross-Over , Método Duplo-Cego , Humanos , Masculino , Desempenho Psicomotor/efeitos dos fármacosRESUMO
RATIONALE: Benzodiazepines slow reasoning performance, but it is still unknown which phase of reasoning is affected and whether this effect is present for different types of relations between entities in reasoning problems. OBJECTIVES: We investigated which phases of deductive reasoning are affected by lorazepam and whether this effect varies according to the type of relations in deductive reasoning problems. METHODS: This was a double-blind, crossover design study of acute oral doses of lorazepam (2 mg) and placebo, using young healthy volunteers. We focused on response delay of three separable phases of deductive reasoning and matched working memory tasks (that involved only maintenance of information) the premise processing phase, the premise integration phase, and the validation phase, in which reasoners decide whether a conclusion logically follows from the premises (reasoning task) or is identical to one of the premises (maintenance task). Type of relations in the premises was also manipulated. We employed material that was difficult to envisage visually and visuospatially ("subiconic") and material easy to envisage visually or visuospatially. RESULTS: Lorazepam slowed response as memory load increased, irrespective of type of relations. It also specifically slowed validation in reasoning problems with visual relations, an effect that disappeared after subtraction of maintenance scores, and increased validation time in problems with subiconic relations, which remained after this subtraction. CONCLUSION: Acute lorazepam administration affected reasoning in two ways: it slowed processing nonspecifically when working memory demands increased and augmented validation time depending on the difficulty in generating and/or manipulating mental representations by the central executive.
Assuntos
Tomada de Decisões/efeitos dos fármacos , Lorazepam/farmacologia , Resolução de Problemas/efeitos dos fármacos , Análise e Desempenho de Tarefas , Administração Oral , Adulto , Análise de Variância , Benzodiazepinas/administração & dosagem , Benzodiazepinas/farmacologia , Estudos Cross-Over , Tomada de Decisões/fisiologia , Método Duplo-Cego , Humanos , Lorazepam/administração & dosagem , Masculino , Rememoração Mental/efeitos dos fármacos , Rememoração Mental/fisiologia , Resolução de Problemas/fisiologia , Tempo de Reação/efeitos dos fármacos , Tempo de Reação/fisiologia , Reprodutibilidade dos Testes , Fatores de TempoRESUMO
OBJECTIVE: The aim of this study was to evaluate the relationship between carpal tunnel syndrome symptoms and compression of the median nerve at the wrist in symptomatic patients. METHODS: A total of 250 patients were selected among those referred for electrodiagnostic evaluation with complaints involving hand or wrist. Primary and secondary symptoms were extracted from the answers to the instrument proposed by Levine et al. [J Bone Joint Surg Am 1993;75:1585]. The association of symptoms and the presence of compression of the median nerve at the wrist were ascertained through a multiple logistic regression test. RESULTS: Secondary symptoms (pain and weakness) were inversely associated with the presence of median nerve compression. Furthermore, primary symptoms (paresthesia, disability and nocturnal symptom) occurred similarly in patients with and without electrophysiologic findings of median nerve compression at the wrist.
Assuntos
Síndrome do Túnel Carpal/diagnóstico , Síndrome do Túnel Carpal/patologia , Neuropatia Mediana/diagnóstico , Neuropatia Mediana/patologia , Condução Nervosa , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Dor/etiologia , Parestesia/etiologia , Sensibilidade e Especificidade , Punho/inervaçãoRESUMO
RATIONALE: There is a dearth of studies which have employed sophisticated paradigms to investigate the effects of zolpidem on memory. OBJECTIVES: To explore anterograde cognitive deficits induced by acute oral doses of zolpidem by means of the process-dissociation procedure (PDP). METHODS: The present study followed a placebo-controlled, double-blind, parallel-group design. Young, healthy females were randomly allocated to one of three treatments with 12 subjects each: placebo, 5 mg and 10 mg zolpidem. Two word-stem completion tasks were carried out close to theoretical peak-plasma concentration: a) direct inclusion task with cued recall, in which participants had to try to use words seen at study to complete stems; and b) direct exclusion task, in which words seen at study were to be avoided as completions. The PDP was applied to the results in these tasks to yield indices of explicit/controlled (C) and implicit/automatic (A) memory. Classical psychometric tests were also carried out. RESULTS: Zolpidem 10 mg led to cognitive effects similar to benzodiazepines (except for the atypical lorazepam), including impairment of exclusion, but not inclusion-task performance. Results of the application of the PDP were inconclusive but concurred with the pattern established in previously published work on benzodiazepine effects, i.e. that zolpidem (10 mg) impaired C. CONCLUSIONS: Zolpidem leads to cognitive effects similar to most benzodiazepines. Although the application of PDP in drug studies may be counterproductive in view of methodological difficulties that are discussed, the pattern of effects on the stem-completion tasks involved in this paradigm is potentially useful in the investigation of cognitive effects of psychoactive drugs.
Assuntos
Agonistas GABAérgicos/efeitos adversos , Transtornos da Memória/induzido quimicamente , Piridinas/efeitos adversos , Administração Oral , Adulto , Análise de Variância , Relação Dose-Resposta a Droga , Método Duplo-Cego , Feminino , Humanos , Transtornos da Memória/fisiopatologia , Rememoração Mental/efeitos dos fármacos , Medição da Dor/métodos , Psicometria/métodos , Análise e Desempenho de Tarefas , Aprendizagem Verbal/efeitos dos fármacos , ZolpidemRESUMO
OBJECTIVE: To evaluate exercise test responses in hypokalaemic periodic paralysis (HPP), to determine its value as a diagnostic tool and the factors that could affect the responses. METHODS: 22 subjects were studied from two families with HPP caused by R528H mutation, four patients with thyrotoxic periodic paralysis, 15 normal controls, and four controls with hyperthyroidism. All family members were submitted to clinical evaluation, electrophysiological exercise testing, and DNA analysis. Patients with thyrotoxic periodic paralysis had exercise tests before and after treatment of their hyperthyroidism. RESULTS: Abnormal responses to the exercise tests were obtained only in subjects with recent attacks of weakness. They were not correlated with genotype, as asymptomatic carriers were unaffected. Patients with thyrotoxic periodic paralysis showed pronounced impairment while they were hyperthyroid, but improved when they were euthyroid. One patient with HPP and chronic KCl use had an increase in amplitude potentials over approximately 20 minutes, possibly related to alteration of potassium homeostasis. CONCLUSIONS: The exercise test is a useful diagnostic test for periodic paralysis, but in the absence of recent weakness negative results must be viewed with caution. It has advantages over the DNA test in being a non-invasive functional test that can provide insights into abnormalities of muscle excitability.
Assuntos
Teste de Esforço , Paralisia Periódica Hipopotassêmica/diagnóstico , DNA/análise , Diagnóstico Diferencial , Progressão da Doença , Eletrofisiologia , Genótipo , Humanos , Paralisia Periódica Hipopotassêmica/genética , Paralisia Periódica Hipopotassêmica/patologia , Debilidade Muscular/fisiopatologia , Linhagem , Sensibilidade e EspecificidadeRESUMO
Lorazepam has been reported to atypically disrupt visual processing compared to other benzodiazepines (BZs), but it is not known to what extent this effect extends to impairment in other modalities. Our objective was to compare the effects of lorazepam with those of flunitrazepam, a BZ with standard effects, on visual and auditory event-related potentials (ERPs) using the same paradigm. The study followed a placebo-controlled, double-blind, parallel group-design and involved single oral doses of lorazepam (2.0 mg), flunitrazepam (1.2 mg) and placebo. Thirty-six young, healthy subjects completed a test battery before and after treatment including classic behavioural tests, visual and auditory ERPs. Both drugs led to comparable alterations on behavioural tests and double-dissociations were found, indicating that the doses used were equipotent: lorazepam was more deleterious than flunitrazepam and placebo in fragmented shape identification, while simple reaction times were prolonged for flunitrazepam in comparison to lorazepam and placebo. Effects on P3 latencies were also distinct: alterations in both modalities for flunitrazepam were equivalent and greater than placebo's. In contrast, lorazepam at the frontal and central electrode sites led to greater changes in visual than in auditory latency, and also to longer visual latencies than flunitrazepam and placebo, but lorazepam's auditory latency effects were only different to placebo's at the parietal electrode site. Peripheral visual changes were not responsible for these effects. Differences in the impairment profile between equipotent doses of lorazepam and flunitrazepam suggests that lorazepam induces atypical central visual processing changes.
Assuntos
Ansiolíticos/efeitos adversos , Potenciais Evocados Auditivos/efeitos dos fármacos , Potenciais Evocados Visuais/efeitos dos fármacos , Flunitrazepam/efeitos adversos , Lorazepam/efeitos adversos , Adolescente , Adulto , Análise de Variância , Cognição/efeitos dos fármacos , Método Duplo-Cego , Feminino , Humanos , Masculino , Desempenho Psicomotor/efeitos dos fármacos , Fatores de TempoRESUMO
We reviewed some physiological aspects of the F-wave studies, mainly related to the motoneurone sizes involved in the generation of this potentials and the number of stimuli necessary to analyze the F-wave parameters. F-wave latencies and F-wave conduction velocities obtained in a group of normal volunteers and in a group of diabetic patients are analyzed.
Assuntos
Diabetes Mellitus Tipo 1/fisiopatologia , Condução Nervosa , Tempo de Reação , Nervo Ulnar/fisiopatologia , Adolescente , Estudos de Casos e Controles , Nefropatias Diabéticas/diagnóstico , Nefropatias Diabéticas/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Neurônios Motores/fisiologiaRESUMO
Ulnar nerve F-waves were studied in 23 healthy volunteers and 27 diabetic patients. Latencies and chronodispersion were analyzed in each group. In the diabetic group all the parameters were normal in 14 patients (52%) and in 13 (48%) at least one parameter was altered. In these patients the most frequently altered parameter was the maximum latency (92%), followed by mean latency (85%), minimum latency (54%) and chronodispersion (54%). These findings suggest that maximum and mean latencies are better parameters to be analyzed in ulnar F-wave studies than minimum latency.