Do nociceptive stimulation intensity and temporal predictability influence pain-induced corticospinal excitability modulation?

Temporal predictability and intensity of an impending nociceptive input both shape pain experience and modulate laser-evoked potentials (LEPs) amplitude. However, it remains unclear whether and how these two factors could influence pain-induced corticospinal excitability modulation. The current study investigated the influence of nociceptive stimulation intensity and temporal predictability on motor-evoked potentials (MEPs) modulation, in parallel to their effect on pain perception and LEPs amplitude. Twenty participants completed electroencephalographic and transcranial magnetic stimulation experiments during which two laser nociceptive stimulation intensities (high and low) were either unpredictably delivered (random delay) or preceded by a fixed-timing cue (fixed delay). The amplitude of the conditioned MEPs was significantly reduced only for the high nociceptive stimulation and was not affected by the temporal predictability of pain (despite the fact that temporal predictability modulated the amplitude of P2 LEP component amplitude). However, a posteriori analyses based on patterns of pain-induced MEPs modulation revealed that participants in which nociceptive stimulation resulted in an increase in corticospinal excitability were more affected by the predictability of pain (i.e. increasing corticospinal excitability even more when pain occurrence was predictable), regardless of the nociceptive stimulation intensity; whereas participants in which nociceptive stimulation resulted in a decrease in corticospinal excitability were sensitive to the intensity of the stimulation but not its predictability. These results suggest a potential influence of cognitive factors such as temporal predictability on the response of the motor system in the presence of pain for some participants, contributing to explain, at least in part, the high variability highlighted in a number of previous studies.