Spinal spatial integration of nociception and its functional role assessed via the nociceptive withdrawal reflex and psychophysical measures in healthy humans

Abstract

Many pain-related conditions are characterized by poorly localized pain areas in the body which is likely to reflect abnormal processing of spatial characteristics of the noxious phenomenon driving the condition (Gran, 2003; Graven-Nielsen & Arendt-Nielsen, 2010; Kamaleri et al., 2008; Wolfe et al., 1990). Within the spinal cord, several primary afferents converge onto spinal neurons and constitute the first relay for somatosensory integration. Electrophysiological studies in animals have shown that neurons located in this first relay play a role in

Spinal temporal and spatial integration of multiple nociceptive input assessed by the Nociceptive Withdrawal Reflex in humans

“…Animal studies confirmed that spinal neuronal networks indeed encode spatial characteristics of the stimulus to elaborate a reflex response [148]. Similarly, the results of Study I [1] seem to indicate that spinal nociceptive processing integrates spatial information of the stimulus to elaborate the optimal reflex response in healthy humans. Whether that information is preserved through the whole integrative process, and whether it becomes available to the human subjective experience of pain, remains elusive to clarify.…”

“…Evidence of spatial summation assessed via the NWR in healthy humans is scarce. Study I [1]showed that paired stimulation elicits significantly larger NWR than single stimulation. The magnitude of the NWR increased 73% when the area of stimulation doubled in size, suggesting SS in the NWR pathway.…”

“…Evidence from human [140] and animal [97], [147] studies suggest that mechanisms of inhibition between RRF indeed exist. In Study I [1], a schematic model of inhibition between lateral RRF is presented that might explain the observed results.…”

“…Study I: "Spinal spatial integration of nociception and its functional role assessed via the nociceptive withdrawal reflex and psychophysical measures in healthy humans" [1] There is an apparent agreement in the literature that SSP is a key phenomenon behind encoding pain intensity. The NWR, at the same time, has a strong defensive behavioral value that would most likely benefit from an analogous spatial summation (SS) mechanism.…”

“…As discussed before, SS due to neuronal recruitment might be optimally facilitated separating the paired stimuli, since the probability of stimulating different RFs increases. In Study I [1], different IEDs were used ("IED 1"=1.5cm, "IED 2"=3cm, "IED 3"=4.5cm, "IED 4"=6cm) to assess the effect of distance on the spatial integration. A significant effect of distance was found, and post hoc comparison confirmed that smaller IEDs induce significantly larger NWR.…”