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Showing papers on "Summation published in 2020"


Journal ArticleDOI
TL;DR: The results confirm that no crosstalk exists between the eyes and that the system can reliably separate the stimuli presented to the eyes, and introduce a stimulus phase shift, which reduced the binocular CFF in normally sighted subjects.

7 citations


Journal ArticleDOI
TL;DR: The measured interaction between conditioned pain modulation and temporal summation of pain supports the participant-controlled temperature approach as a promising method to explore dynamic inhibitory and facilitatory pain processes previously undetected by rating-based approaches.
Abstract: OBJECTIVE Descending pain modulation can be experimentally assessed by way of testing conditioned pain modulation. The application of tonic heat as a test stimulus in such paradigms offers the possibility of observing dynamic pain responses, such as adaptation and temporal summation of pain. Here we investigated conditioned pain modulation effects on tonic heat employing participant-controlled temperature, an alternative tonic heat pain assessment. Changes in pain perception are thereby represented by temperature adjustments performed by the participant, uncoupling this approach from direct pain ratings. Participant-controlled temperature has emerged as a reliable and sex-independent measure of tonic heat. METHODS Thirty healthy subjects underwent a sequential conditioned pain modulation paradigm, in which a cold water bath was applied as the conditioning stimulus and tonic heat as a test stimulus. Subjects were instructed to change the temperature of the thermode in response to variations in perception to tonic heat in order to maintain their initial rating over a two-minute period. Two additional test stimuli (i.e., lower limb noxious withdrawal reflex and pressure pain threshold) were included as positive controls for conditioned pain modulation effects. RESULTS Participant-controlled temperature revealed conditioned pain modulation effects on temporal summation of pain (P = 0.01). Increased noxious withdrawal reflex thresholds (P = 0.004) and pressure pain thresholds (P < 0.001) in response to conditioning also confirmed inhibitory conditioned pain modulation effects. CONCLUSIONS The measured interaction between conditioned pain modulation and temporal summation of pain supports the participant-controlled temperature approach as a promising method to explore dynamic inhibitory and facilitatory pain processes previously undetected by rating-based approaches.

5 citations


Journal ArticleDOI
TL;DR: By the NWR, spatial summation was shown to affect the nociceptive processing within the spinal cord, and the inhibited motor response obtained when simultaneously stimulating the medial and lateral side of the sole of the foot suggests the presence of an inhibitory mechanism with a functional, behaviorally oriented function.
Abstract: Animal studies have previously shown that deep dorsal horn neurons play a role in the processing of spatial characteristics of nociceptive information in mammals. Human studies have supported the role of the spinal neurons; however, the mechanisms involved, and its significance, remain to be clarified. The aim of this study was to investigate spatial aspects of the spinal integration of concurrent nociceptive electrical stimuli in healthy humans using the Nociceptive Withdrawal Reflex (NWR) as an objective indication of spinal nociceptive processing. Fifteen healthy volunteers participated in the study. Electrical stimuli were delivered, using five electrodes located across the sole of the foot in a mediolateral disposition, as a single or double simultaneous stimuli with varying Inter-Electrode Distances (IEDs). The stimulation intensity was set at 1.5× NWR threshold (TA muscle). The size of the NWR was quantified in the 60-180 ms poststimulus window as a primary outcome measure. Psychophysical measures were secondary outcomes. Single stimulation elicited significantly smaller NWRs and perceived intensity than double stimulation (p < .01), suggesting the presence of spatial summation occurring within the spinal processing. During double stimulation, increasing the inter-electrode distance produced significantly smaller NWR sizes (p < .05) but larger pain intensity ratings (p < .05). By the NWR, spatial summation was shown to affect the nociceptive processing within the spinal cord. The inhibited motor response obtained when simultaneously stimulating the medial and lateral side of the sole of the foot suggests the presence of an inhibitory mechanism with a functional, behaviorally oriented function.

4 citations


Posted ContentDOI
16 Jul 2020-bioRxiv
TL;DR: The aim of this study was to describe the SSp effect as a function of the size of a stimulated area(s) and investigate the effect of pain intensity on SSp, and to evaluate the influence of the SS type on the magnitude of SSp.
Abstract: Pain intensity is difficult to predict. Mostly, because of modulatory processes underlying its formation. For example, when nociceptive stimulation occupies a larger body area, pain increases disproportionally. This modulation is called spatial summation of pain (SSp) and is responsible for coding pain intensity. To predict pain based on spatial variables, a profound understanding of the SSp effect is crucial. The aim of this study was i) to describe the SSp effect as a function of the size (or distance) of a stimulated area(s), ii) to investigate the effect of pain intensity on SSp and iii) to evaluate the influence of the SS type on the magnitude of SSp. Thirty-one healthy participants took part in a within-subject experiment. Participants were exposed to area- and distanced based SSp. In the former, electrocutaneous noxious stimuli were applied by up to 5 electrodes (5 areas) forming a line-like pattern at the ulnar side of the hand, while in the latter the same position and lengths of stimuli were used but only two electrodes were stimulated (5 separations). Each paradigm was repeated using pain of low, moderate and high intensity in a random and counterbalanced order. Each stimulus was assessed on a 0-100 scale. It was found that the pattern of increase in pain followed a logarithmic rather than a linear function. The dynamics of the pain increase were statistically different across pain intensities, with more summation occurring, if stimuli were calibrated to eliciting 9high9 pain. SSp was resistant to saturation in the area-based but not in the distance-based SSp, where 0.8cm separation between two electrodes produced a similar pain intensity as 1.6cm and 2.4cm. Results indicate that area-based SSp is more painful than distance-based SSp when low and moderate but not when high pain intensity is induced. Presented findings have important implications for all studies, in which the spatial dimension of pain is measured. When the area or separation between nociceptive stimulation increases, pain does not increase linearly. Furthermore, the pattern of the pain increase depends on i) intensity and ii) the number of sites of nociception. In conclusion, a logarithmic function should be considered when predicting the size of a nociceptive source. This pattern is indicative for inhibitory processes underlying SSp.