RESUMO
Spatial integration of cold pressor pain (CPP) in the hand was studied in healthy human subjects by measuring the latency to the ice water-induced first pain sensation with and without conditioning CPP. CPP alone showed a marked spatial summation effect. When conditioning and test CPP were applied at the same time, conditioning CPP suppressed test CPP both in an adjacent and a distant site. When test CPP was applied after the conditioning CPP (i.e. pain induced by conditioning CPP was considerably stronger than that evoked by test CPP) conditioning CPP suppressed the test CPP only in a distant site but enhanced it in an adjacent site. A decrease in the test stimulus area increased the suppressive effect by conditioning CPP. Thus, CPP shows spatial summation or inhibition depending on experimental parameters.
Assuntos
Vias Aferentes/fisiologia , Temperatura Baixa/efeitos adversos , Nociceptores/fisiologia , Dor/fisiopatologia , Pele/inervação , Adulto , Vasos Sanguíneos/inervação , Vasos Sanguíneos/fisiologia , Sistema Nervoso Central/fisiologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Condução Nervosa/fisiologia , Limiar da Dor/fisiologia , Estimulação Física , Tempo de Reação/fisiologia , Transmissão Sináptica/fisiologiaRESUMO
The effect of stimulus duration and frequency on subjective sensations evoked by electrical tooth stimulation was studied in 12 subjects. The sensory responses were classified using 5 equi-sensation categories (perception threshold, prepain, pain threshold, moderate pain, intense pain). Both continuously increasing and randomised stimuli were applied. A comparison was made with the activation thresholds of intradental A- and C-fibres in the cat. The mean threshold of intradental A-fibres was lower than the perception threshold at all pulse durations. Perception threshold decreased with increasing stimulus frequency. Current intensities which evoked prepain at a stimulus frequency of 1 Hz were rated as pain at 20 Hz. At supraliminal pain levels the effects of summation were more marked. High-frequency stimulation produced intense pain sensations at intensities well below the activation thresholds of pulpal C-fibres in the cat. We conclude that both perception and pain thresholds and supraliminal pain are modified by temporal summation, and that activation of different pulpal fibre populations is not responsible for production of prepain and pain sensations.
