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.