Heterotopic nociceptive conditioning stimuli and mental task modulate differently the perception and physiological correlates of short CO2 laser stimuli

Abstract

The present study was aimed at examining the specificity of the action of heterotopic nociceptive conditioning stimulation (HNCS) by comparing its effects of those induced by a mental task (MT). Five test stimuli made from short CO2 laser pulses (duration: 40 msec; diameter: 10 mm; intensity: 0.25-0.8 Joules) were delivered every 30 to 45 sec at random to 4 different spots on the skin of the upper lip in 3 groups of 10 healthy subjects. The two most intense stimuli were perceived as painful, the two least intense stimuli as warm, and the intermediate stimulus as hot or near painful. Perception (VAS), reaction time (T) and cerebral evoked potentials (CEPs) were monitored before, during and after conditioning stimulation consisting either of HNCS (hand submerged in cold water) or of MT (arithmetic subtraction). Pain perception (first pain) threshold was increased in both conditioning stimulations; however, the stimulus-response curve and the neurophysiological correlates were differently affected. During HNCS, the stimulus-response curve was depressed and T was increased mainly for the intermediate stimulus, whilst CEP power density was reduced for all stimulus intensities; discrimination performance near pain threshold was dramatically depressed. During MT, the stimulus-response curve was shifted down toward higher stimulus intensities, T was equally increased for all stimulus intensities, whereas CEP power density was not changed; discrimination performance remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Nociceptive Steady-State Evoked Potentials Elicited by Rapid Periodic Thermal Stimulation of Cutaneous Nociceptors

“…At the energies used in the present study, this laser is able to generate laser pulses with a highly reproducible energy output (variance from trial to trial, Ͻ1%) (Plaghki et al, 1994). The irradiance profile of the laser beam has a Gaussian shape.…”

Neurophysiological observation of the nociceptive system using electrocutaneous stimulation

“…For both SP and PT, the difference between NRS scores of CPT and control was different for all stimulus amplitudes or NoP. Unequal inhibition effects by CPT were also reported for laser stimuli with changing energy [115]. Largest effect of CPT were found near pain threshold and no effect for stimuli below pain threshold [115].…”

“…Unequal inhibition effects by CPT were also reported for laser stimuli with changing energy [115]. Largest effect of CPT were found near pain threshold and no effect for stimuli below pain threshold [115]. On the contrary, laser modulating stimuli resulted in almost equal inhibitory effects regardless of stimulus amplitudes of electrical tooth stimulation [111].…”

“…Late EP components can also be influenced by attention or distraction. Furthermore, Plaghki et al [115] obtained inhibition of EEG and subjective rating by both a CPT and mental task but in a dissimilar manner. In the present study, subjects were asked to focus their attention to the electrical stimuli by rating each of them during both control and CPT.…”

“…The DNIC can be induced by diverse tonic noxious stimulation methods, such as ischemic tourniquet pressure [46], capsaicin [150] or cold pressor test (CPT) [115]. Ischemic tourniquet pressure produces pain by inflating a tourniquet for a couple of minutes.…”