Postpulse effects on blink reflex responses.
The technique of paired stimulation is routinely used in many laboratories in the assessment of the excitability recovery curve of the blink reflex. Other effects, such as prepulse inhibition or classical conditioning, can also be investigated with repeated presentation of pairs of time-locked stimuli. Regularly repeated presentations of an unpleasant stimulus may give rise to a transient excitability enhancement in neural structures in the reflex circuit. We have investigated whether such a transient shift in excitability can be demonstrated before the actual stimulus is applied. In 10 normal volunteers, we regularly alternated series of 5 trials containing an auditory tone of mild intensity with series of the same auditory tone followed by a relatively strong supraorbital nerve electrical stimulus. We calculated the habituation percentage of the orbicularis oculi responses to the auditory stimulus within a series and compared the results obtained in series containing the auditory tone alone with those from series containing the auditory tone followed by the electrical stimulus. Habituation was significantly less with paired stimulation than with the auditory tone alone, the mean area of the response to the 3rd trial in percentage of that to the first trial being 34.0 +/- 16.4% for paired stimuli, and 20.3 +/- 14.1% for auditory stimulus alone (P = 0.008). This effect, induced by the presence of an impending electrical stimulus on the response to a preceding stimulus, is defined as a postpulse effect in contradistinction to the prepulse effects induced by a weak stimulus on the response to a subsequent startle-eliciting stimulus. When a paradigm with a stimulus pair is used in human subjects, the possibility of effects occurring in both temporal directions should be taken into account. Blink reflex responses to a given stimulus may exhibit excitability changes induced by a preceding or by an impending stimulus.
Valls-Solé
J
J
Departament de Medicina, Universitat de Barcelona, Spain.
Hallett
M
M
Alvarez
R
R
D000161:Acoustic Stimulation; D000328:Adult; D001767:Blinking / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006185:Habituation, Psychophysiologic / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors