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Frahm KS, Andersen OK, Arendt-Nielsen L, Gervasio S, Mørch CD. Topical capsaicin modulates the two-point discrimination threshold-Modulation depends on stimulation modality and intensity. Eur J Pain 2024. [PMID: 39116004 DOI: 10.1002/ejp.4701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 06/07/2024] [Accepted: 07/04/2024] [Indexed: 08/10/2024]
Abstract
BACKGROUND Spatial acuity concerns the ability to localize and discriminate sensory input and is often tested using the two-point discrimination threshold (2PDT). Sensitization of the pain system can affect the spatial acuity, but it is unclear how 2PDTs of different testing modalities are affected. The aim was to investigate if the 2PDTs for mechanical and heat stimulation at different intensities were modulated by topical capsaicin sensitization. METHODS 30 healthy subjects were divided into either a capsaicin or a placebo group. The 2PDT was tested using two different modalities, mechanical and thermal (laser) delivered at innocuous and noxious intensities. The 2PDT were determined at baseline and re-assessed 48 h later. In the follow-up session, the subjects either had a capsaicin patch (8%) or placebo patch placed in the testing area for 30 min before re-testing the 2PDT. RESULTS The 2PDT was highly dependent on stimulation modality and intensity. The lowest 2PDT was found for innocuous mechanical stimuli (40.0 mm, 95% CI 38.1-41.9 mm), and the highest 2PDT was found for innocuous thermal stimuli (81.7 mm, 95% CI 73.9-89.5 mm). Topical capsaicin generally increased the 2PDT, but this was only significant for innocuous mechanical stimuli. The perceived intensity of the stimuli was increased following capsaicin and was generally higher for noxious stimuli than for innocuous stimuli (ANOVA, p < 0.001). CONCLUSIONS This study showed that capsaicin provoked pain sensitization increased the 2PDT. The 2PDT tested using innocuous mechanical stimuli showed less variable results indicating that this test is most suitable to detect this aspect of spatial acuity. SIGNIFICANCE STATEMENT This study investigated how the two-point discrimination threshold (2PDT) can be modulated by topical capsaicin. The 2PDT was assessed for two different modalities (thermal and mechanical) and for two different intensities (innocuous and noxious) before and after capsaicin. The results showed that the 2PDT was generally impaired following capsaicin, but this was only significant for mechanical innocuous stimuli. Furthermore, it was shown that mechanical innocuous stimuli assessed the 2PDT with lower variability than other combinations.
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Affiliation(s)
- Ken Steffen Frahm
- Integrative Neuroscience Group, CNAP-Center for Neuroplasticity and Pain, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Ole Kæseler Andersen
- Integrative Neuroscience Group, CNAP-Center for Neuroplasticity and Pain, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Lars Arendt-Nielsen
- Translational Pain Biomarkers, CNAP-Center for Neuroplasticity and Pain, SMI®, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
- Department of Gastroenterology & Hepatology, Mech-Sense, Department of Clinical Medicine, Aalborg University Hospital, Aalborg, Denmark
- Steno Diabetes Center North Denmark, Aalborg University Hospital, Aalborg, Denmark
| | - Sabata Gervasio
- Neural Engineering and Neurophysiology Group, SMI®, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Carsten Dahl Mørch
- Integrative Neuroscience Group, CNAP-Center for Neuroplasticity and Pain, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
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Henrich MC, Garenfeld MA, Malesevic J, Strbac M, Dosen S. Encoding contact size using static and dynamic electrotactile finger stimulation: natural decoding vs. trained cues. Exp Brain Res 2024; 242:1047-1060. [PMID: 38467759 PMCID: PMC11078849 DOI: 10.1007/s00221-024-06794-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Accepted: 01/24/2024] [Indexed: 03/13/2024]
Abstract
Electrotactile stimulation through matrix electrodes is a promising technology to restore high-resolution tactile feedback in extended reality applications. One of the fundamental tactile effects that should be simulated is the change in the size of the contact between the finger and a virtual object. The present study investigated how participants perceive the increase of stimulation area when stimulating the index finger using static or dynamic (moving) stimuli produced by activating 1 to 6 electrode pads. To assess the ability to interpret the stimulation from the natural cues (natural decoding), without any prior training, the participants were instructed to draw the size of the stimulated area and identify the size difference when comparing two consecutive stimulations. To investigate if other "non-natural" cues can improve the size estimation, the participants were asked to enumerate the number of active pads following a training protocol. The results demonstrated that participants could perceive the change in size without prior training (e.g., the estimated area correlated with the stimulated area, p < 0.001; ≥ two-pad difference recognized with > 80% success rate). However, natural decoding was also challenging, as the response area changed gradually and sometimes in complex patterns when increasing the number of active pads (e.g., four extra pads needed for the statistically significant difference). Nevertheless, by training the participants to utilize additional cues the limitations of natural perception could be compensated. After the training, the mismatch in the activated and estimated number of pads was less than one pad regardless of the stimulus size. Finally, introducing the movement of the stimulus substantially improved discrimination (e.g., 100% median success rate to recognize ≥ one-pad difference). The present study, therefore, provides insights into stimulation size perception, and practical guidelines on how to modulate pad activation to change the perceived size in static and dynamic scenarios.
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Affiliation(s)
- Mauricio Carlos Henrich
- Department of Health Science and Technology, Aalborg University, Selma Lagerløfs Vej 249, 9260, Gistrup, Denmark
| | - Martin A Garenfeld
- Department of Health Science and Technology, Aalborg University, Selma Lagerløfs Vej 249, 9260, Gistrup, Denmark
| | | | - Matija Strbac
- Tecnalia Serbia Ltd, Deligradska 9/39, 11000, Belgrade, Serbia
| | - Strahinja Dosen
- Department of Health Science and Technology, Aalborg University, Selma Lagerløfs Vej 249, 9260, Gistrup, Denmark.
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Rujoie A, Andersen OK, Frahm KS. Investigation of directional discrimination in the nociceptive system using temperature-controlled laser stimuli. Eur J Pain 2024. [PMID: 38440936 DOI: 10.1002/ejp.2259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 01/30/2024] [Accepted: 02/26/2024] [Indexed: 03/06/2024]
Abstract
BACKGROUND Cutaneous laser stimulation has commonly been employed to investigate the thermal properties of the nociceptive system. The aim of this study was to investigate how a temperature-controlled laser system improves the assessment of directional discrimination in the nociceptive system. METHODS In total, twenty healthy volunteers participated in this study. To determine the directional discrimination threshold (stimulation length 50% correct, expressed in mm), thermal stimuli were delivered using a diode laser and the laser beam was perpendicularly displaced across the skin to give a linear stimulation in four different directions (distal, proximal, lateral and medial) and displacement lengths (3 for lateral-medial and 5 for distal-proximal). Two temperature control modes were used in the stimulation system, open-loop and closed-loop control. The subjects had to report the perceived stimulus direction, the degree of certainty regarding the perceived direction and the intensity of the perceived stimulus (0-10 numerical rating scale, 3: pain threshold). RESULTS During closed-loop control, the orientation of stimuli was discriminated significantly more accurately than during open-loop control. During closed-loop control, the directional discrimination threshold was 31.9 and 26.1 mm for distal-proximal and lateral-medial directed stimuli, respectively. A numerical rating scale was significantly higher for the lateral/medial directions. Moreover, the variability of the discrimination threshold is reduced in the closed-loop control system. CONCLUSIONS The findings show that discrimination ability is better in the lateral-medial directions compared to the distal-proximal directions. This study indicates that using a system enabling closed-loop temperature control, allows more robust probing of the temporo-spatial mechanisms in the nociceptive system. SIGNIFICANCE This study shows that a newly developed temperature-controlled laser stimulation system enhances the possibilities to investigate the nociceptive temporo-spatial integration, as shown by a less variable directional discrimination threshold. The results also show that different orthogonal directions are discriminated differently. This new method allows a better investigation of the combined temporal and spatial mechanisms in the nociceptive system.
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Affiliation(s)
- Ahmad Rujoie
- Integrative Neuroscience Group, Center for Neuroplasticity and Pain (CNAP), Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - Ole Kaeseler Andersen
- Integrative Neuroscience Group, Center for Neuroplasticity and Pain (CNAP), Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - Ken Steffen Frahm
- Integrative Neuroscience Group, Center for Neuroplasticity and Pain (CNAP), Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
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Mohamadi M, Meftahi N, Javidi-Alsaadi P. Comparison of tactile acuity between patients with chronic patellofemoral pain with central sensitization and healthy persons: A cross-sectional study. Physiother Theory Pract 2024:1-7. [PMID: 38165123 DOI: 10.1080/09593985.2023.2300040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Accepted: 12/21/2023] [Indexed: 01/03/2024]
Abstract
BACKGROUND Patellofemoral pain (PFP) is a common multifactorial condition in young and physically active people. OBJECTIVE The occurrence of central sensitization may play an important role in sensory disturbance. This study was designed to investigate, in patients with chronic PFP, the presence of disturbances in tactile acuity with central sensitization. METHODS Thirty patients with chronic PFP and 30 matched healthy controls entered this cross-sectional study. Graphesthesia (numerical score), two-point discrimination (mm), and point-to-point sensation (mm) were assessed in all participants. RESULTS The results of between-group comparisons showed that there were significant differences between the involved knee in patients with chronic PFP and healthy participants in graphesthesia (median = 13 [case], 19 [control]; p < .001), two-point discrimination (median = 25.8 [case], 20.3 [control]; p < .001), and point-to-point sensation (median = 14.5 [case], 6.2 [control]; p < .001). There was also a significant difference in graphesthesia between the non-involved knee in patients with chronic PFP and healthy participants (median = 17 [case], 19 [control]; p = .003). The results of within-group comparisons revealed a significant difference in graphesthesia, two-point discrimination, and point-to-point sensation between the involved and non-involved knee in patients with chronic PFP (p < .001). Moreover, there was a positive correlation between two-point discrimination and pain in patients with chronic PFP (r = 0.446, p = .014). CONCLUSION The findings of this study reveal that there is a sensory deficit in patients with chronic PFP. Because sensory information is necessary for motor control and pain perception, we can assume that clinical symptoms in these patients are related to sensory deficits.
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Affiliation(s)
- Marzieh Mohamadi
- Rehabilitation Research Center, Department of Physiotherapy, School of Rehabilitation Sciences, Shiraz University of Medical Sciences, Shiraz, Fars, Iran
| | - Narges Meftahi
- Rehabilitation Research Center, Department of Physiotherapy, School of Rehabilitation Sciences, Shiraz University of Medical Sciences, Shiraz, Fars, Iran
| | - Pouria Javidi-Alsaadi
- Rehabilitation Research Center, Department of Physiotherapy, School of Rehabilitation Sciences, Shiraz University of Medical Sciences, Shiraz, Fars, Iran
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Frahm KS, Gervasio S, Arguissain F, Mouraux A. Influence of skin type and laser wavelength on laser-evoked potentials. Eur J Pain 2023; 27:1226-1238. [PMID: 37358263 DOI: 10.1002/ejp.2152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 05/03/2023] [Accepted: 06/08/2023] [Indexed: 06/27/2023]
Abstract
BACKGROUND Infrared laser stimulation is a valuable tool in pain research, its primary application being the recording of laser-evoked brain potentials (LEPs). Different types of laser stimulators, varying in their skin penetrance, are likely to have a large influence on the LEPs, when stimulating different skin types. The aim of this study was to investigate how LEPs depend on laser type and skin location. METHODS Two different laser stimulators (CO2 and Nd:YAP) were used to compare LEPs in healthy subjects. Stimuli were delivered to the hand dorsum and palm to investigate the effects of skin type on the evoked responses. Stimulus-evoked brain responses were recorded using EEG and perceived intensity ratings were recorded. Computational modelling was used to investigate the observed differences. RESULTS LEPs evoked by stimulation of the hairy skin were similar between CO2 and Nd:YAP stimulation. In contrast, LEPs elicited from the palm were markedly different and barely present for CO2 stimulation. There was a significant interaction between laser type and skin type (RM-ANOVA, p < 0.05) likely due to smaller CO2 LEPs in the palm. CO2 stimuli to the palm also elicited significantly lower perceived intensities. The computational model showed that the observed differences were explainable by the laser absorption characteristics and skin thickness affecting the temperature profile at the dermo-epidermal junction (DEJ). CONCLUSIONS This study shows that LEP elicitation depends on the combination of laser penetrance and skin type. Low penetrance stimuli, from a CO2 laser, elicited significantly lower LEPs and perceived intensities in the palm. SIGNIFICANCE This study showed that the elicitation of laser-evoked potentials in healthy humans greatly depends on the combination of laser stimulator type and skin type. It was shown that high penetrance laser stimuli are capable of eliciting responses in both hairy and glabrous skin, whereas low penetrance stimuli barely elicited responses from the glabrous skin. Computational modelling was used to demonstrate that the results could be fully explained by the combination of laser type and skin thickness.
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Affiliation(s)
- Ken Steffen Frahm
- Integrative Neuroscience Group, CNAP - Center for Neuroplasticity and Pain, SMI©, Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - Sabata Gervasio
- Neural Engineering and Neurophysiology Group, SMI©, Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - Federico Arguissain
- Integrative Neuroscience Group, CNAP - Center for Neuroplasticity and Pain, SMI©, Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - André Mouraux
- Université Catholique de Louvain, Institute of Neuroscience (IoNS), Faculty of Medicine, Bruxelles, Belgium
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Valette R, Gonzalez-Vargas J, Dosen S. The impact of walking on the perception of multichannel electrotactile stimulation in individuals with lower-limb amputation and able-bodied participants. J Neuroeng Rehabil 2023; 20:108. [PMID: 37592336 PMCID: PMC10436512 DOI: 10.1186/s12984-023-01234-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 08/09/2023] [Indexed: 08/19/2023] Open
Abstract
BACKGROUND One of the drawbacks of lower-limb prostheses is that they do not provide explicit somatosensory feedback to their users. Electrotactile stimulation is an attractive technology to restore such feedback because it enables compact solutions with multiple stimulation points. This allows stimulating a larger skin area to provide more information concurrently and modulate parameters spatially as well as in amplitude. However, for effective use, electrotactile stimulation needs to be calibrated and it would be convenient to perform this procedure while the subject is seated. However, amplitude and spatial perception can be affected by motion and/or physical coupling between the residual limb and the socket. In the present study, we therefore evaluated and compared the psychometric properties of multichannel electrotactile stimulation applied to the thigh/residual limb during sitting versus walking. METHODS The comprehensive assessment included the measurement of the sensation and discomfort thresholds (ST & DT), just noticeable difference (JND), number of distinct intervals (NDI), two-point discrimination threshold (2PD), and spatial discrimination performance (SD). The experiment involved 11 able-bodied participants (4 females and 7 males; 29.2 ± 3.8 years), 3 participants with transtibial amputation, and 3 participants with transfemoral amputation. RESULTS In able-bodied participants, the results were consistent for all the measured parameters, and they indicated that both amplitude and spatial perception became worse during walking. More specifically, ST and DT increased significantly during walking vs. sitting (2.90 ± 0.82 mA vs. 2.00 ± 0.52 mA; p < 0.001 for ST and 7.74 ± 0.84 mA vs. 7.21 ± 1.30 mA; p < 0.05 for DT) and likewise for the JND (22.47 ± 12.21% vs. 11.82 ± 5.07%; p < 0.01), while the NDI became lower (6.46 ± 3.47 vs. 11.27 ± 5.18 intervals; p < 0.01). Regarding spatial perception, 2PD was higher during walking (69.78 ± 17.66 mm vs. 57.85 ± 14.87 mm; p < 0.001), while the performance of SD was significantly lower (56.70 ± 10.02% vs. 64.55 ± 9.44%; p < 0.01). For participants with lower-limb amputation, the ST, DT, and performance in the SD assessment followed the trends observed in the able-bodied population. The results for 2PD and JND were however different and subject-specific. CONCLUSION The conducted evaluation demonstrates that electrotactile feedback should be calibrated in the conditions in which it will be used (e.g., during walking). The calibration during sitting, while more convenient, might lead to an overly optimistic (or in some cases pessimistic) estimate of sensitivity. In addition, the results underline that calibration is particularly important in people affected by lower-limb loss to capture the substantial variability in the conditions of the residual limb and prosthesis setup. These insights are important for the implementation of artificial sensory feedback in lower-limb prosthetics applications.
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Affiliation(s)
- Romain Valette
- Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | | | - Strahinja Dosen
- Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
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Adamczyk WM, Katra M, Szikszay TM, Peugh J, King CD, Luedtke K, Coghill RC. Spatial Tuning in Nociceptive Processing Is Driven by Attention. THE JOURNAL OF PAIN 2023; 24:1116-1125. [PMID: 36965648 PMCID: PMC10330125 DOI: 10.1016/j.jpain.2023.03.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 03/07/2023] [Accepted: 03/13/2023] [Indexed: 03/27/2023]
Abstract
When the source of nociception expands across a body area, the experience of pain increases due to the spatial integration of nociceptive information. This well-established effect is called spatial summation of pain (SSp) and has been the subject of multiple investigations. Here, we used cold-induced SSp to investigate the effect of attention on the spatial tuning of nociceptive processing. Forty pain-free volunteers (N = 40, 20 females) participated in this experiment. They took part in an SSp paradigm based on three hand immersions into cold water (5°C): Participants either immersed the radial segment ("a"), ulnar segment ("b") or both hand segments ("a+b") and provided overall pain ratings. In some trials based on "a+b" immersions, they were also asked to provide divided (ie, first pain in "a" then in "b"; or reversed) and directed attention ratings (ie, pain only in "a" or "b"). Results confirmed a clear SSp effect in which reported pain during immersions of "a" or "b" was less intense than pain during immersions of "a+b" (P < .001). Data also confirmed that spatial tuning was altered. SSp was abolished when participants provided two ratings in a divided fashion (P < .001). Furthermore, pain was significantly lower when attention was directed only to one segment ("a" OR "b") during "a+b" immersion (P < .001). We conclude that spatial tuning is dynamically driven by attention as reflected in abolished SSp. Directed attention was sufficient to focus spatial tuning and abolish SSp. Results support the role of cognitive processes such as attention in spatial tuning. PERSPECTIVE: This article presents experimental investigation of spatial tuning in pain and offers mechanistic insights of contiguous spatial summation of pain in healthy volunteers. Depending on how pain is evaluated in terms of attentional derivative (overall pain, directed, divided attention) the pain is reduced and spatial summation abolished.
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Affiliation(s)
- Waclaw M Adamczyk
- Pediatric Pain Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Pediatrics, University of Cincinnati School of Medicine, Cincinnati, Ohio; Laboratory of Pain Research, Institute of Physiotherapy and Health Sciences, The Jerzy Kukuczka Academy of Physical Education, Katowice, Poland.
| | - Michal Katra
- Laboratory of Pain Research, Institute of Physiotherapy and Health Sciences, The Jerzy Kukuczka Academy of Physical Education, Katowice, Poland
| | - Tibor M Szikszay
- Department of Physiotherapy, Pain and Exercise Research Lübeck (P.E.R.L.), Institute of Health Sciences, Universität zu Lübeck, Lübeck, Germany
| | - James Peugh
- Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Pediatrics, University of Cincinnati School of Medicine, Cincinnati, Ohio
| | - Christopher D King
- Pediatric Pain Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Pediatrics, University of Cincinnati School of Medicine, Cincinnati, Ohio
| | - Kerstin Luedtke
- Laboratory of Pain Research, Institute of Physiotherapy and Health Sciences, The Jerzy Kukuczka Academy of Physical Education, Katowice, Poland; Department of Physiotherapy, Pain and Exercise Research Lübeck (P.E.R.L.), Institute of Health Sciences, Universität zu Lübeck, Lübeck, Germany
| | - Robert C Coghill
- Pediatric Pain Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Pediatrics, University of Cincinnati School of Medicine, Cincinnati, Ohio
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Rujoie A, Andersen OK, Frahm KS. A novel temperature-controlled laser system to uniformly activate cutaneous thermal receptors during movable thermal stimulation. J Neural Eng 2023; 20. [PMID: 36638531 DOI: 10.1088/1741-2552/acb2f9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 01/13/2023] [Indexed: 01/15/2023]
Abstract
Objective. Laser stimulators have been widely used in pain studies to selectively activate Aδand C nociceptors without coactivation of mechanoreceptors. Temperature-controlled laser systems have been implemented with low-temperature variations during stimulations, however, these systems purely enabled stationary stimulation. This study aimed to implement, test and validate a new laser stimulation system that controls skin temperature by continuously adjusting laser output during stimulus movement to allow accurate investigation of tempo-spatial mechanisms in the nociceptive system.Approach. For validation, laser stimuli were delivered to the right forearm of eight healthy subjects using a diode laser. The laser beam was displaced across the skin to deliver a moving thermal stimulation to the skin surface. To test the function and feasibility of the system, different stimulation parameters were investigated involving two control modes (open-loop and closed-loop), three displacement velocities (5, 10 and 12 mm s-1), two intensities (high 46 °C and low 42 °C), two stimulus lengths (20 and 100 mm) and two directions (distal and proximal).Main results. During closed-loop control, the stimulation error and variation of stimulation temperatures were significantly smaller than during open-loop control. The standard deviation of stimulation temperatures increased significantly with stimulation intensity and displacement length.Significance. This study showed that more accurate, less variable laser stimulations were delivered to the skin using closed-loop control during a movable stimulus. The more uniform skin temperature during stimuli is likely to ensure a more uniform nociceptor activation.
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Affiliation(s)
- Ahmad Rujoie
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - Ole Kæseler Andersen
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
| | - Ken Steffen Frahm
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Department of Health Science & Technology, Aalborg University, Aalborg, Denmark
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Henrich MC, Frahm KS, Andersen OK. Spinal spatial integration of nociception and its functional role assessed via the nociceptive withdrawal reflex and psychophysical measures in healthy humans. Physiol Rep 2021; 8:e14648. [PMID: 33217191 PMCID: PMC7679129 DOI: 10.14814/phy2.14648] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 10/20/2020] [Accepted: 10/23/2020] [Indexed: 12/11/2022] Open
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.
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Affiliation(s)
- Mauricio Carlos Henrich
- Integrative Neuroscience, Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Aalborg University, Aalborg Ø, Denmark
| | - Ken Steffen Frahm
- Integrative Neuroscience, Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Aalborg University, Aalborg Ø, Denmark
| | - Ole Kaeseler Andersen
- Integrative Neuroscience, Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Aalborg University, Aalborg Ø, Denmark
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Henrich MC, Frahm KS, Andersen OK. Tempo-spatial integration of nociceptive stimuli assessed via the nociceptive withdrawal reflex in healthy humans. J Neurophysiol 2021; 126:373-382. [PMID: 34191609 DOI: 10.1152/jn.00155.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spatial information of nociceptive stimuli applied in the skin of healthy humans is integrated in the spinal cord to determine the appropriate withdrawal reflex response. Double-simultaneous stimulus applied in different skin sites are integrated, eliciting a larger reflex response. The temporal characteristics of the stimuli also modulate the reflex, e.g., by temporal summation. The primary aim of this study was to investigate how the combined tempo-spatial aspects of two stimuli are integrated in the nociceptive system. This was investigated by delivering single- and double-simultaneous stimulation and sequential stimulation with different interstimulus intervals (ISIs ranging 30-500 ms) to the sole of the foot of 15 healthy subjects. The primary outcome measure was the size of the nociceptive withdrawal reflex (NWR) recorded from the tibialis anterior (TA) and biceps femoris (BF) muscles. Pain intensity was measured using a numerical rating scale (NRS) scale. Results showed spatial summation in both TA and BF when delivering simultaneous stimulation. Simultaneous stimulation provoked larger reflexes than sequential stimulation in TA, but not in BF. Larger ISIs elicited significantly larger reflexes in TA, whereas the opposite pattern occurred in BF. This differential modulation between proximal and distal muscles suggests the presence of spinal circuits eliciting a functional reflex response based on the specific tempo-spatial characteristics of a noxious stimulus. No modulation was observed in pain intensity ratings across ISIs. Absence of modulation in the pain intensity ratings argues for an integrative mechanism located within the spinal cord governed by a need for efficient withdrawal from a potentially harmful stimulus.NEW & NOTEWORTHY Tempo-spatial integration of electrical noxious stimuli was studied using the nociceptive withdrawal reflex and a perceived intensity. Tibialis anterior and biceps femoris muscles were differentially modulated by the temporal characteristics of the stimuli and stimulated sites. These findings suggest that spinal neurons are playing an important role in the tempo-spatial integration of nociceptive information, leading to a reflex response that is distributed across multiple spinal cord segments and governed by an efficient defensive withdrawal strategy.
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Affiliation(s)
- Mauricio Carlos Henrich
- Integrative Neuroscience, Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Ken Steffen Frahm
- Integrative Neuroscience, Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Ole Kæseler Andersen
- Integrative Neuroscience, Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
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Frahm KS, Gervasio S. The two-point discrimination threshold depends both on the stimulation noxiousness and modality. Exp Brain Res 2021; 239:1439-1449. [PMID: 33682043 DOI: 10.1007/s00221-021-06068-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 02/18/2021] [Indexed: 11/30/2022]
Abstract
The two-point discrimination threshold (2PDT) has been used to investigate the integration of sensory information, especially in relation to spatial acuity. The 2PDT has been investigated for both innocuous mechanical stimuli and noxious thermal stimuli; however, previous studies used different stimulation modalities to compare innocuous and noxious stimuli. This study investigated the 2PDT in 19 healthy participants, using both thermal (laser) and mechanical stimulation modalities. Within each modality, both innocuous and noxious intensities were applied. Concurrent point stimuli were applied to the right volar forearm, with separation distances of 0-120 mm, in steps of 10 mm. 0 mm corresponds to a single point. Following each stimulus, the participants indicated the number of perceived points (1 or 2) and the perceived intensity (NRS: 0: no perception, 3: pain threshold, 10: maximum pain). The order of stimulation modality, intensity and distance was randomized. The 2PDT for innocuous and noxious mechanical stimuli was 34.7 mm and 47.1 mm, respectively. For thermal stimuli, the 2PDT was 80.5 mm for innocuous stimuli and 66.9 mm for noxious stimuli. The average NRS for thermal stimuli was 1.6 for innocuous intensities and 4.0 for noxious intensities, while for mechanical stimuli, the average NRS was 0.9 for innocuous intensities and 3.6 for noxious intensities. This study showed that the 2PDT highly depends on both stimulation modality and intensity. Within each modality, noxious intensities modulates the 2PDT differently, i.e., noxious intensities lowers the 2PDT for thermal stimuli, but increases the 2PDT for mechanical stimuli.
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Affiliation(s)
- Ken Steffen Frahm
- Department of Health Science and Technology, Integrative Neuroscience group, CNAP-Center for Neuroplasticity and Pain, SMI®, Aalborg University, Fredrik Bajersvej 7D3, 9220, Aalborg, Denmark.
| | - Sabata Gervasio
- Neural Engineering and Neurophysiology Group, SMI®, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
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12
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Adamczyk WM, Szikszay TM, Kung T, Carvalho GF, Luedtke K. Not as "blurred" as expected? Acuity and spatial summation in the pain system. Pain 2021; 162:794-802. [PMID: 32925592 PMCID: PMC7920491 DOI: 10.1097/j.pain.0000000000002069] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 08/27/2020] [Accepted: 08/28/2020] [Indexed: 11/27/2022]
Abstract
ABSTRACT Spatial acuity measured by 2-point discrimination (2PD) threshold and spatial summation of pain (SSp) are useful paradigms to probe the pain system in humans. Whether the results of these paradigms are influenced by different stimulus modalities and intensities is unclear. The aim of this study was to test 2PD controlling the stimulus modality and the intensity and to investigate the effect of modality on SSp. Thirty-seven healthy volunteers were tested for 2PDs with 2 stimulus modalities (electrocutaneous and mechanical) and intensity (noxious and innocuous). For each condition, participants received stimuli to either 1 or 2 points on their lower back with different distances (2-14 cm, steps of 2 cm). It was found that 2PDs were significantly smaller for noxious stimuli for both modalities. By contrast, between-modality comparison reproduced previous reports of impaired acuity for noxious stimulation. Higher pain intensities were reported when a larger area was stimulated (SSp), independent of the modality. Furthermore, reported pain intensities were higher when the distance between 2 stimulated areas was increased from 2 to 6 cm (P < 0.001), 8 cm (P < 0.01), and 14 cm (P < 0.01). 2PDs determined by mechanical and electrocutaneous stimuli were significantly correlated within both stimulus intensities, ie, innocuous (r = 0.34, P < 0.05) and noxious (r = 0.35, P < 0.05). The current results show 3 novel findings: (1) the precision of the pain system might be higher than in the innocuous (tactile) system when mechanical and electrocutaneous modalities are used, (2) the pattern of distance-based and area-based SSp seems to be comparable irrespective of the modality applied (mechanical and electrocutaneous), and (3) both modalities are moderately correlated.
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Affiliation(s)
- Wacław M. Adamczyk
- Department of Health Sciences, Academic Physiotherapy, Pain and Exercise Research Luebeck (P.E.R.L.), University of Luebeck, Luebeck, Germany
- Center of Brain, Behavior and Metabolism (CBBM), University of Luebeck, Luebeck, Germany
- Laboratory of Pain Research, Institute of Physiotherapy and Health Sciences, The Jerzy Kukuczka Academy of Physical Education, Katowice, Poland
| | - Tibor M. Szikszay
- Department of Health Sciences, Academic Physiotherapy, Pain and Exercise Research Luebeck (P.E.R.L.), University of Luebeck, Luebeck, Germany
- Center of Brain, Behavior and Metabolism (CBBM), University of Luebeck, Luebeck, Germany
| | - Tiffany Kung
- BSc Study Program, University of Alberta, Edmonton, AB, Canada
| | | | - Kerstin Luedtke
- Department of Health Sciences, Academic Physiotherapy, Pain and Exercise Research Luebeck (P.E.R.L.), University of Luebeck, Luebeck, Germany
- Center of Brain, Behavior and Metabolism (CBBM), University of Luebeck, Luebeck, Germany
- Laboratory of Pain Research, Institute of Physiotherapy and Health Sciences, The Jerzy Kukuczka Academy of Physical Education, Katowice, Poland
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Iwasaki Y, Ando K, Iizuka S, Kitazaki M, Iwata H. Detachable Body: The Impact of Binocular Disparity and Vibrotactile Feedback in Co-Presence Tasks. IEEE Robot Autom Lett 2020. [DOI: 10.1109/lra.2020.2977320] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Frahm K, Mørch C, Andersen O. Directional discrimination is better for noxious laser stimuli than for innocuous laser stimuli. Eur J Pain 2019; 24:742-751. [DOI: 10.1002/ejp.1521] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 11/29/2019] [Accepted: 12/06/2019] [Indexed: 11/09/2022]
Affiliation(s)
- K.S. Frahm
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), SMI®, Dept. of Health Science & Technology Aalborg University Aalborg Denmark
| | - C.D. Mørch
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), SMI®, Dept. of Health Science & Technology Aalborg University Aalborg Denmark
| | - O.K. Andersen
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), SMI®, Dept. of Health Science & Technology Aalborg University Aalborg Denmark
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Frahm KS, Mørch CD, Andersen OK. Cutaneous nociceptive sensitization affects the directional discrimination – but not the 2-point discrimination. Scand J Pain 2019; 19:605-613. [DOI: 10.1515/sjpain-2018-0344] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 03/28/2019] [Indexed: 11/15/2022]
Abstract
Abstract
Background and aims
Several pain conditions have been shown to reduce the discriminative abilities of external stimuli. The aim of this study was to investigate how cutaneous sensitization affects the tempo-spatial discrimination for both painful laser stimulation and mechanical stimulation.
Methods
Fifteen healthy subjects were presented with two different stimulation paradigms, a continuous line stimulation and a 2-point stimulation. Line stimulations were delivered in two different directions in lengths of 25, 50, 75, and 100 mm. Two-point distances from 0 to 100 mm were tested. The subjects reported the perceived intensity, and either direction (line stimulations) or number of perceived points (2-point stimulations). All stimuli were tested both before and after topical capsaicin (8% concentration) sensitization (30 min).
Results
All mechanical line stimulations were reported correctly before capsaicin and 3 stimulations (out of 240) were reported incorrectly after capsaicin. For the laser line stimulation, the directional discrimination threshold (DDT) was 69.5 mm before capsaicin and 76.3 mm after capsaicin. The 2-point discrimination threshold for laser stimulation was 70.3 mm before capsaicin and 68.0 mm after, for the mechanical stimuli it was 31.5 mm before capsaicin and 31.0 mm after capsaicin. The perceived intensities were increased for the laser line stimulations after capsaicin (linear mixed model (LMM), p < 0.001) and increased with stimulation length (LMM, p < 0.001). For mechanical stimuli, NRS was increased following capsaicin (LMM, p < 0.001). The intensities for both mechanical and laser 2-point stimuli increased after capsaicin and increased with distance between points (LMM, p < 0.01).
Conclusions
The findings show how cutaneous sensitization appears to affect directional discrimination to a larger extent than the 2-point discrimination.
Implications
This study is the first to investigate how directional discrimination is altered during sensitization. If such measures can be optimized they may provide a new method to probe the neural mechanisms in pain patients.
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Affiliation(s)
- Ken Steffen Frahm
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), SMI , Department of Health Science and Technology , Aalborg University , Fredrik Bajersvej 7D3 (Office A2-204) , Aalborg , Denmark , Phone: +45 99 40 98 42
| | - Carsten Dahl Mørch
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), SMI , Department of Health Science and Technology , Aalborg University , Aalborg , Denmark
| | - Ole Kæseler Andersen
- Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), SMI , Department of Health Science and Technology , Aalborg University , Aalborg , Denmark
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O’Neill S, Larsen JB, Nim C, Arendt-Nielsen L. Topographic mapping of pain sensitivity of the lower back – a comparison of healthy controls and patients with chronic non-specific low back pain. Scand J Pain 2018; 19:25-37. [DOI: 10.1515/sjpain-2018-0113] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Accepted: 08/27/2018] [Indexed: 11/15/2022]
Abstract
Abstract
Background and aims
The choice of testing site for quantitative sensory testing (QST) of pain sensitivity is important and previous studies have demonstrated patterns in pain sensitivity within discrete areas in different body regions. Some areas are characterized by a relatively high degree of spatial pain discrimination and recognizable patterns of pain referral, whilst others are not. The lumbar region is likely to have relatively low pain acuity and overlapping of pain referral. The current study was conducted to determine whether patterns of pain sensitivity (detection thresholds) could be identified in the lower back, whether differences in such patterns exist between different groups and whether such patterns could help identify a clinical source of pain and localized increased pain sensitivity.
Methods
Twenty-one patients with non-specific chronic low back pain and 21 healthy controls were tested for pressure and heat pain thresholds on 30 pre-defined locations over the mid and lower back. Topographical maps of mean pain thresholds and variability were produced, inspected visually and analyzed statistically. Between group differences in pain threshold were analyzed statistically as an indicator of widespread increased pain sensitivity. Evidence of segmental increased pain sensitivity was examined by group statistical comparison of mid-line lower range.
Results
A clear pattern of higher pain thresholds in the mid-line was evident in both groups and for both pain modalities. No discernible patterns were evident for variability within groups, but marked differences were seen between groups: variability for pressure pain thresholds appeared similar between groups, however for heat pain threshold, variability was uniformly low in the control group and uniformly high in the patient group. A highly significant (p<0.0001) difference in pain thresholds for pressure and heat was found with patients exhibiting lower thresholds than controls. No between group difference was found for mid-line lower range for either modality (p>0.05).
Conclusions
The current study supports previous findings of widespread, increased pain sensitivity in chronic non-specific low-back pain patients. It also indicates that there are discernible and similar topographical patterns of pain sensitivity in the dorsal area in both groups, but that this pattern is related to the lateral position of the test site and not the segmental level. Specific segments with increased pain sensitivity could not be identified in the patient group, which casts doubt on the utility of pressure and heat pain thresholds as indicators of the clinical source of spinal pain – at least in a population of chronic non-specific low-back pain.
Implications
In a cohort of chronic non-specific low-back pain patients and with the chosen methodology, topographical QST mapping in the lumbar region does not appear useful for identifying the spinal segment responsible for clinical pain, but it does demonstrate widespread group differences in pain sensitivity.
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Affiliation(s)
- Søren O’Neill
- Spinecenter of Southern Denmark, Lillebælt Hospital, Østre Hougvej 55 , Middelfart DK-5500 , Denmark
- Institute of Regional Health Research, University of Southern Denmark, Campusvej 55 , Odense M DK-5230 , Denmark , Phone: +45 4043 2004
| | - Johanne Brinch Larsen
- Institute of Regional Health Research, University of Southern Denmark , Odense M , Denmark
- Spinecenter of Southern Denmark, Lillebælt Hospital , Middelfart , Denmark
| | - Casper Nim
- Institute of Regional Health Research, University of Southern Denmark , Odense M , Denmark
- Spinecenter of Southern Denmark, Lillebælt Hospital , Middelfart , Denmark
| | - Lars Arendt-Nielsen
- Centre for Sensory-Motor Interaction, School of Medicine , University of Aalborg , Aalborg , Denmark
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Abstract
Spatial summation of pain (SSP) is the increase of perceived intensity that occurs as the stimulated area increases. Spatial summation of pain is subadditive in that increasing the stimulus area produces a disproportionately small increase in the perceived intensity of pain. A possible explanation for subadditive summation may be that convergent excitatory information is modulated by lateral inhibition. To test the hypothesis that lateral inhibition may limit SSP, we delivered different patterns of noxious thermal stimuli to the abdomens of 15 subjects using a computer-controlled CO2 laser. Lines (5 mm wide) of variable lengths (4, 8 cm) were compared with 2-point stimuli delivered at the same position/separation as the length of lines. When compared with one-point control stimuli, 2-point stimulus patterns produced statistically significant SSP, while no such summation was detected during line stimulus patterns. Direct comparison of pain intensity evoked by 2-point pattern stimuli with line pattern stimuli revealed that 2-point patterns were perceived as significantly more painful, despite the fact that the 2-point pattern stimulated far smaller areas of skin. Thus, the stimulation of the skin region between the endpoints of the lines appears to produce inhibition. These findings indicate that lateral inhibition limits SSP and is an intrinsic component of nociceptive information processing. Disruption of such lateral inhibition may contribute substantially to the radiation of some types of chronic pain.
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Ligato D, Petersen K, Mørch C, Arendt-Nielsen L. Offset analgesia: The role of peripheral and central mechanisms. Eur J Pain 2018; 22:142-149. [DOI: 10.1002/ejp.1110] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Affiliation(s)
- D. Ligato
- Center for Sensory-Motor Interaction (SMI); Department of Health Science and Technology; Faculty of Medicine; Aalborg University; Denmark
| | - K.K. Petersen
- Center for Sensory-Motor Interaction (SMI); Department of Health Science and Technology; Faculty of Medicine; Aalborg University; Denmark
| | - C.D. Mørch
- Center for Sensory-Motor Interaction (SMI); Department of Health Science and Technology; Faculty of Medicine; Aalborg University; Denmark
| | - L. Arendt-Nielsen
- Center for Sensory-Motor Interaction (SMI); Department of Health Science and Technology; Faculty of Medicine; Aalborg University; Denmark
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19
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20
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Comparison of spatial summation properties at different body sites. Scand J Pain 2017; 17:126-131. [DOI: 10.1016/j.sjpain.2017.07.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 07/03/2017] [Accepted: 07/07/2017] [Indexed: 11/17/2022]
Abstract
Abstract
Background and aims
The nociceptive system appears to have evolved a range of protective characteristics that are of great interest in understanding both acute and chronic pain. Spatial summation is one important characteristic, whereby increasing area of a stimulus, or distance between multiple stimuli, results in more intense pain—not only greater area of pain. One of the mysteries of chronic pain is why spinal pain is so prevalent relative to pain at other sites. Since pathological tissue models have failed to fully explain spinal pain, we theorized that body region specific differences in sensory processing—such as a greater propensity for spatial summation—may help to explain its vulnerability. We aimed to examine this by comparing the properties of summation at different body parts: the dorsal forearm, neck, and back.
Methods
Spatial summation of pain was investigated using noxious intra-dermal electrical stimuli in healthy pain-free adults (14 males, 6 females), and the perceived pain intensity was rated on a 0-100 pain scale. Area-based stimulation was investigated by doubling the stimulation area with the addition of a second electrode placed adjacent to the first. Distance-based summation was investigated by randomly varying the separation distance between paired noxious electrical stimuli at separations of 0,10,15, and 20 cm.
Results
This study demonstrated that the properties of area- and distance-based summation are uniform across the neck, back, and forearm in healthy adults. Spatial summation of pain was also found to be greatest at 15- and 20-cm paired separations for all body regions tested, confirming that noxious information can be integrated over an extensive anatomical area.
Conclusion
Data from this investigation refutes the thesis that spatial summation of pain may be a contributing factor for the reported difference in chronicity rates between spinal and peripheral sites. It remains, however, a potentially important mechanism by which noxious inputs from multi-level pathology might integrate and contribute to pain.
Implications
While data from this project suggest that there are no regional differences in the properties of spatial summation of noxious stimuli, regional differences in other characteristics of the nociceptive system may yet provide insight into why some spinal pain is so highly prevalent; nociceptive distance-based summation may be highly relevant where two or more conditions co-exist in close proximity.
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Franceschi M, Seminara L, Dosen S, Strbac M, Valle M, Farina D. A System for Electrotactile Feedback Using Electronic Skin and Flexible Matrix Electrodes: Experimental Evaluation. IEEE TRANSACTIONS ON HAPTICS 2017; 10:162-172. [PMID: 27775538 DOI: 10.1109/toh.2016.2618377] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Myoelectric prostheses are successfully controlled using muscle electrical activity, thereby restoring lost motor functions. However, the somatosensory feedback from the prosthesis to the user is still missing. The sensory substitution methods described in the literature comprise mostly simple position and force sensors combined with discrete stimulation units. The present study describes a novel system for sophisticated electrotactile feedback integrating advanced distributed sensing (electronic skin) and stimulation (matrix electrodes). The system was tested in eight healthy subjects who were asked to recognize the shape, trajectory, and direction of a set of dynamic movement patterns (single lines, geometrical objects, letters) presented on the electronic skin. The experiments demonstrated that the system successfully translated the mechanical interaction into the moving electrotactile profiles, which the subjects could recognize with a good performance (shape recognition: 86±8% lines, 73±13% geometries, 72±12% letters). In particular, the subjects could identify the movement direction with a high confidence. These results are in accordance with previous studies investigating the recognition of moving stimuli in human subjects. This is an important development towards closed-loop prostheses providing comprehensive and sophisticated tactile feedback to the user, facilitating the control and the embodiment of the artificial device into the user body scheme.
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22
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Distinct temporal filtering mechanisms are engaged during dynamic increases and decreases of noxious stimulus intensity. Pain 2016; 156:1906-1912. [PMID: 26035254 PMCID: PMC4770340 DOI: 10.1097/j.pain.0000000000000250] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Offset analgesia could be activated with a feedback-controlled near-infrared laser system. Larger and delayed response to temperature decrease than to temperature increase was observed. Physical stimuli are subject to pronounced temporal filtering during afferent processing such that changes occurring at certain rates are amplified and others are diminished. Temporal filtering of nociceptive information remains poorly understood. However, the phenomenon of offset analgesia, where a disproportional drop in perceived pain intensity is caused by a slight drop in noxious heat stimulation, indicates potent temporal filtering in the pain pathways. To develop a better understanding of how dynamic changes in a physical stimulus are constructed into an experience of pain, a transfer function between the skin temperature and the perceived pain intensity was modeled. Ten seconds of temperature-controlled near-infrared (970 nm) laser stimulations above the pain threshold with a 1°C increment, decrement, or constant temperature were applied to the dorsum of the hand of healthy human volunteers. The skin temperature was assessed by an infrared camera. Offset analgesia was evoked by laser heat stimulation. The estimated transfer functions showed shorter latencies when the temperature was increased by 1°C (0.53 seconds [0.52-0.54 seconds]) than when decreased by 1°C (1.15 seconds [1.12-1.18 seconds]) and smaller gains (increase: 0.89 [0.82-0.97]; decrease: 2.61 [1.91-3.31]). The maximal gain was observed at rates around 0.06 Hz. These results show that temperature changes occurring around 0.06 Hz are best perceived and that a temperature decrease is associated with a larger but slower change in pain perception than a comparable temperature increase. These psychophysical findings confirm the existence of differential mechanisms involved in temporal filtering of dynamic increases and decreases in noxious stimulus intensity.
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Stanton TR, Gilpin HR, Reid E, Mancini F, Spence C, Moseley GL. Modulation of pain via expectation of its location. Eur J Pain 2015; 20:753-66. [PMID: 26491945 DOI: 10.1002/ejp.801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/17/2015] [Indexed: 11/07/2022]
Abstract
BACKGROUND The spatial precision of expectancy effects on pain is unclear. We hypothesized that expecting nociceptive stimuli at particular skin sites would have an analgesic effect on nociceptive stimuli presented between them (middle zone). METHODS Laser stimuli (evoking pin-prick pain) were delivered to three discrete skin zones on the forearm, under two conditions. During 'Localization', participants' expectation of stimuli was spatially divided between two locations (expected stimuli in only the outer two skin zones): pain intensity and stimulus location were judged. During 'No-localization' (control condition), participants had no expectation concerning stimulus location; only pain intensity was rated. Additional experiments assessed the importance of the actual location on the forearm by: shifting all skin zones proximally towards the elbow (control for joint proximity, Experiment 2); adding a fourth zone distally (control for interaction between joint proximity and enhanced distal inhibition, Experiment 3). RESULTS All experiments demonstrated spatially specific pain modulation, but only Experiment 2 (near elbow) supported our hypothesis: middle zone pain intensity was significantly lower (p = 0.02) during Localization than No-localization. Experiment 1 (near wrist) found reduced pain intensity during Localization only for the distal zone (p = 0.04). Experiment 3 confirmed this effect: reduced pain during Localization occurred only for the most distal zone (p = 0.046). CONCLUSION Expecting a painful stimulus in non-adjacent skin sites has spatially specific effects on pain modulation, but this reflects an interaction between the expected location of stimulation and the actual location. This suggests a more complex connection between somatotopic maps and nociceptive modulation than previously thought; several distinct mechanisms likely contribute.
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Affiliation(s)
- T R Stanton
- The Sansom Institute for Health Research, The University of South Australia, Adelaide, Australia
- Neuroscience Research Australia, Sydney, Australia
| | - H R Gilpin
- The Sansom Institute for Health Research, The University of South Australia, Adelaide, Australia
- School of Psychology, The University of Nottingham, UK
| | - E Reid
- The Sansom Institute for Health Research, The University of South Australia, Adelaide, Australia
| | - F Mancini
- Department of Neuroscience, Physiology and Pharmacology, University College London, UK
- Institute of Cognitive Neuroscience, University College London, UK
| | - C Spence
- Crossmodal Research Laboratory, Department of Experimental Psychology, University of Oxford, UK
| | - G L Moseley
- The Sansom Institute for Health Research, The University of South Australia, Adelaide, Australia
- Neuroscience Research Australia, Sydney, Australia
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24
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Coghill RC, Keefe FJ. Quantitative sensory testing in predicting persistent pain after joint replacement surgery. Pain 2015; 156:4-5. [DOI: 10.1016/j.pain.0000000000000025] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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25
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Mancini F, Bauleo A, Cole J, Lui F, Porro CA, Haggard P, Iannetti GD. Whole-body mapping of spatial acuity for pain and touch. Ann Neurol 2014; 75:917-24. [PMID: 24816757 PMCID: PMC4143958 DOI: 10.1002/ana.24179] [Citation(s) in RCA: 145] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 05/08/2014] [Accepted: 05/08/2014] [Indexed: 12/30/2022]
Abstract
Objective Tactile spatial acuity is routinely tested in neurology to assess the state of the dorsal column system. In contrast, spatial acuity for pain is not assessed, having never been systematically characterized. More than a century after the initial description of tactile acuity across the body, we provide the first systematic whole-body mapping of spatial acuity for pain. Methods We evaluated the 2-point discrimination thresholds for both nociceptive-selective and tactile stimuli across several skin regions. Thresholds were estimated using pairs of simultaneous stimuli, and also using successive stimuli. Results and interpretation These two approaches produced convergent results. The fingertip was the area of highest spatial acuity, for both pain and touch. On the glabrous skin of the hand, the gradient of spatial acuity for pain followed that observed for touch. On the hairy skin of the upper limb, spatial acuity for pain and touch followed opposite proximal–distal gradients, consistent with the known innervation density of this body territory. Finally, by testing spatial acuity for pain in a rare participant completely lacking Aβ fibers, we demonstrate that spatial acuity for pain does not rely on a functioning system of tactile primary afferents. This study represents the first systematic characterization of spatial acuity for pain across multiple regions of the body surface. Ann Neurol 2014;75:917–924
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Affiliation(s)
- Flavia Mancini
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London, United Kingdom; Institute of Cognitive Neuroscience, University College London, London, United Kingdom
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26
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Mancini F, Sambo CF, Ramirez JD, Bennett DLH, Haggard P, Iannetti GD. A fovea for pain at the fingertips. Curr Biol 2013; 23:496-500. [PMID: 23477726 PMCID: PMC3778751 DOI: 10.1016/j.cub.2013.02.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Revised: 01/14/2013] [Accepted: 02/04/2013] [Indexed: 11/24/2022]
Abstract
The spatial resolution of sensory systems is not homogeneous across their receptive surfaces. For example, tactile acuity is greatest on the fingertips, reflecting the high innervation density and small mechanoreceptive fields in this area [1, 2]. In contrast, pain is considered to lack any equivalent to the tactile fovea on the fingertips, where the density of nociceptive fibers is remarkably low [3]. Here, by combining psychophysics with histology, we show that this established notion is incorrect. By delivering small-diameter nociceptive-specific laser pulses to human volunteers, we discovered that (1) the spatial acuity for pain is higher on the fingertips than on proximal skin regions such as the hand dorsum, and (2) this distal-proximal gradient for pain is comparable to that for touch. In contrast, skin biopsies in the same participants showed that the intraepidermal nerve fiber density is lower in the fingertips than in the hand dorsum. The increased spatial acuity for pain on the fingertips therefore cannot be explained simply by peripheral innervation density. This finding is, however, consistent with the existence of fine-grained maps of nociceptive input to individual digits in the human primary somatosensory cortex [4]. Video Abstract
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Affiliation(s)
- Flavia Mancini
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK.
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27
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Thullier F, Bolmont B, Lestienne FG. Vibrotactile pattern recognition: a portable compact tactile matrix. IEEE Trans Biomed Eng 2011; 59:525-30. [PMID: 22084044 DOI: 10.1109/tbme.2011.2175483] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Compact tactile matrix (CTM) is a vibrotactile device composed of a seven-by-seven array of electromechanical vibrators "tactip" used to represent tactile patterns applied to a small skin area. The CTM uses a dynamic feature to generate spatiotemporal tactile patterns. The design requirements focus particularly on maximizing the transmission of the vibration from one tactip to the others as well as to the skin over a square area of 16 cm (2) while simultaneously minimizing the transmission of vibrations throughout the overall structure of the CTM. Experiments were conducted on 22 unpracticed subjects to evaluate how the CTM could be used to develop a tactile semantics for communication of instructions in order to test the ability of the subjects to identify: 1) directional prescriptors for gesture guidance and 2) instructional commands for operational task requirements in a military context. The results indicate that, after familiarization, recognition accuracies in the tactile patterns were remarkably precise for more 80% of the subjects.
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Weissman-Fogel I, Brayer-Zwi N, Defrin R. Spatial resolution of the pain system: a proximal-to-distal gradient of sensitivity revealed with psychophysical testing. Exp Brain Res 2011; 216:181-90. [DOI: 10.1007/s00221-011-2924-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 10/20/2011] [Indexed: 12/31/2022]
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Lewis JS, Coales K, Hall J, McCabe CS. ‘Now you see it, now you do not’: sensory–motor re-education in complex regional pain syndrome. HAND THERAPY 2011. [DOI: 10.1258/ht.2011.011005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The patient with complex regional pain syndrome (CRPS) commonly describes a lack of ownership of their painful limb, poor definition of that body part and difficulty with localization of the limb when performing daily activities. These descriptions suggest that sensory input from the limb may be reduced leading to neglect of the limb and poor motor control. However, the cardinal symptom of CRPS is pain, commonly severe, which demands a high level of attention. Patients are highly protective of the painful region and hypervigilant to any potential threats to their affected limb. These seemingly conflicting behavioural responses and sensory descriptions are confusing for the patient and health-care professional. In recent years our understanding has greatly advanced on how altered sensory perception of a CRPS affected limb relates to changes in the central representation of that body part, and how this may interact with motor planning and autonomic function. Excitingly, this increased knowledge has directly informed clinical practice via a new evaluation of sensory–motor re-education techniques and the development of novel interventions to enhance sensory discrimination. We review the common sensory problems seen in CRPS, the mechanisms that may be behind these clinical symptoms, and how sensory, motor and autonomic systems interact. Therapies designed to enhance sensory discrimination and motor planning are discussed, supported by the results of a small case series undergoing sensory re-education for CRPS. The clinical protocol and two case studies are available as additional online material to illustrate how all of this is applied in practice.
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Affiliation(s)
| | - Karen Coales
- The Royal National Hospital for Rheumatic Diseases, Bath, UK
| | - Jane Hall
- The Royal National Hospital for Rheumatic Diseases, Bath, UK
| | - Candida S McCabe
- The Royal National Hospital for Rheumatic Diseases, Bath, UK
- The Faculty of Health and Life Sciences, University of the West of England, Bristol, UK
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Painful numbers – The ability of the pain system to encode complex skin stimuli. Pain 2010; 151:7-8. [DOI: 10.1016/j.pain.2010.06.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Accepted: 06/26/2010] [Indexed: 11/19/2022]
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