Effects of diffuse noxious inhibitory controls on temporal summation of the RIII reflex in humans

Abstract

The aim of this study was to investigate the effects of diffuse noxious inhibitory controls (DNICs) on the temporal summation of the nociceptive flexion reflex (RIII reflex) in humans. Recordings were obtained from 36 healthy adults (16 M, 20 F), and the area and temporal summation threshold (TST) of the RIII reflex were measured. The subjective intensity of the painful sensation was rated on an 11-point visual analogue scale (VAS). Neurophysiological and VAS measurements were recorded after activation of DNICs by means of the cold pressor test (CPT), which involved immersing the hand in cold water (2-4 degrees C). A slight significant lower TST was found in the females versus the males. In all the subjects, the CPT induced a significant TST increase and RIII area reduction compared with the control session. The VAS results paralleled those of the RIII reflex area and TST. During the CPT, a significant difference in the percentage TST increase emerged between females and males, being lower in the former. Similarly, we found a significantly lower percentage reduction of the RIII area in women than in men during the CPT. To summarize, activation of DNICs through the CPT significantly increased the TST of the RIII reflex in healthy subjects. This inhibitory effect was gender-specific. Whereas other findings are based on psychophysical evaluations, the results of this experimental study provide an objective neurophysiological demonstration that DNICs attenuate temporal summation in humans and confirm the presence of significant differences in pain modulation mechanisms between men and women.

Hip-phase-dependent flexion reflex modulation and expression of spasms in patients with spinal cord injury

“…The temporal summation of the flexion reflex in humans following repeated electrical stimulation is due mainly to a summation of inputs from A-delta and C-fibers (see review of Sandrini et al, 2005). Thus, absence of this phenomenon in this study might be attributed to different stimulation protocols employed in this study compared to others (Serrao et al, 2004;Andersen et al, 2005).…”

Altered processing of sensory stimuli in patients with migraine

“…112,113 Temporal summation of pain develops in parallel with tem poral summation of the NWR of the lower limbs, reflected by a progressive increase in magnitude of the NWR after constant intensity electrical stimula tion (which activates both Aδ and C fibres, [113][114][115] and is inhibited by N methyl d aspartate receptor antago nists). 116 Interestingly, descending pain control systems modulate temporal summation of the NWR, 117 and might be dysfunctional in a number of chronic pain dis orders, including migraine. For example, studies of tem poral summation of the NWR in people with migraine show facilitation of temporal pain processing between attacks.…”

Sex differences in endogenous pain modulation by distracting and painful conditioning stimulation

“…All other female subjects were tested during the follicular phase of their menstrual cycle (days 3 through 11) to reduce group heterogeneity in gonadal hormone levels, which may influence pain perception (Riley et al 1999). Testing during the follicular phase was selected because sex differences between males and follicular phase females have been observed for numerous pain measures, including pain threshold, temporal summation of pain, and endogenous analgesia (Goolkasian 1980;Sarlani et al 2004;Serrao et al 2004;Kowalczyk et al 2006). Informed consent was obtained from all subjects prior to experimentation.…”

“…Demonstration of sex differences in endogenous pain modulation among healthy subjects would provide support for this hypothesis. However, the few studies examining this issue have produced conflicting results, with some reporting reduced hypoalgesic magnitude (Staud et al 2003;Serrao et al 2004) or duration (Ge et al 2004) in women, and others reporting no sex differences (France and Suchowiecki 1999;Baad-Hansen et al 2005;Pud et al 2005). …”