Perceptual, cognitive and motor responses to contact heat stimuli

Abstract

Objective Afferent inputs in humans lead to a trace of excitability in the corresponding sensory channel, perception, cognition and prepared motor responses. We investigated how the events related to each of these aspects of sensory processing are affected by stimulus intensity. Methods Nine healthy subjects performed a wrist extension reaction time (RT) task experiment in front of the Libet’s clock in order to assess the time at which they perceived the contact heat stimulus used as imperative signal (awareness = AW). We recorded also the thermoalgesic evoked potentials (N2/P2). Stimuli were either strong (52 °C) or mild (42 °C). We monitored RT, N2 latency, amplitude of N2–P2, and the time of AW for each stimulation condition. Results Usual order of responses was RT, AW, N2. N2–P2 amplitude had a negative correlation with AW ( p Conclusions Reaction time is executed as soon as the imperative signal is processed, while a late cognitive response does not depend on stimulus intensity. Key message The test used allows for separation of perceptual levels in humans.