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Gusso MM, Christison-Lagay KL, Zuckerman D, Chandrasekaran G, Kronemer SI, Ding JZ, Freedman NC, Nohama P, Blumenfeld H. More than a feeling: Scalp EEG and eye signals in conscious tactile perception. Conscious Cogn 2022; 105:103411. [PMID: 36156359 DOI: 10.1016/j.concog.2022.103411] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 08/22/2022] [Accepted: 08/28/2022] [Indexed: 01/27/2023]
Abstract
Understanding the neural basis of consciousness is a fundamental goal of neuroscience, and sensory perception is often used as a proxy for consciousness in empirical studies. However, most studies rely on reported perception of visual stimuli. Here we present behavior, high density scalp EEG and eye metric recordings collected simultaneously during a novel tactile threshold perception task. We found significant N80, N140 and P300 event related potentials in perceived trials and in perceived versus not perceived trials. Significance was limited to a P100 and P300 in not perceived trials. We also found an increase in pupil diameter and blink rate and a decrease in microsaccade rate following perceived relative to not perceived tactile stimuli. These findings support the use of eye metrics as a measure of physiological arousal associated with conscious perception. Eye metrics may also represent a novel path toward the creation of tactile no-report tasks in the future.
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Affiliation(s)
- Mariana M Gusso
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA; Programa de Pós-Graduação em Tecnologia em Saúde, Pontifícia Universidade Católica do Paraná, R. Imaculada Conceição, 1155, Prado Velho, Curitiba, Paraná 80215-901, Brazil
| | - Kate L Christison-Lagay
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - David Zuckerman
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Ganesh Chandrasekaran
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Sharif I Kronemer
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA; Departments of Interdepartmental Neuroscience Program, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Julia Z Ding
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Noah C Freedman
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Percy Nohama
- Programa de Pós-Graduação em Tecnologia em Saúde, Pontifícia Universidade Católica do Paraná, R. Imaculada Conceição, 1155, Prado Velho, Curitiba, Paraná 80215-901, Brazil
| | - Hal Blumenfeld
- Departments of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA; Departments of Interdepartmental Neuroscience Program, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA; Departments of Neuroscience, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA; Departments of Neurosurgery, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
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The capsaicin receptor TRPV1 is the first line defense protecting from acute non damaging heat: a translational approach. J Transl Med 2020; 18:28. [PMID: 31952468 PMCID: PMC6966804 DOI: 10.1186/s12967-019-02200-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 12/26/2019] [Indexed: 02/07/2023] Open
Abstract
Background Pain is the vital sense preventing tissue damage by harmful noxious stimuli. The capsaicin receptor TRPV1 is activated by noxious temperatures, however, acute heat pain is only marginally affected in mice after TRPV1 knockout but completely eliminated in mice lacking TRPV1 positive fibers. Exploring contribution of candidate signal transduction mechanisms to heat pain in humans needs translational models. Methods We used focused, non-damaging, short near-infrared laser heat stimuli (wavelength 1470/1475 nm) to study the involvement of TRPV1-expressing nerve fibers in the encoding of heat pain intensity. Human psychophysics (both sexes) were compared to calcium transients in native rat DRG neurons and heterologously expressing HEK293 cells. Results Heating of dermal and epidermal nerve fibers in humans with laser stimuli of ≥ 2.5 mJ (≥ 25 ms, 100 mW) induced pain that increased linearly as a function of stimulus intensity in double logarithmic space across two orders of magnitude and was completely abolished by desensitization using topical capsaicin. In DRG neurons and TRPV1-expressing HEK cells, heat sensitivity was restricted to capsaicin sensitive cells. Strength duration curves (2–10 ms range) and thresholds (DRGs 0.56 mJ, HEK cells 0.52 mJ) were nearly identical. Tachyphylaxis upon repetitive stimulation occurred in HEK cells (54%), DRGs (59%), and humans (25%). Conclusion TRPV1-expressing nociceptors encode transient non-damaging heat pain in humans, thermal gating of TRPV1 is similar in HEK cells and DRG neurons, and TRPV1 tachyphylaxis is an important modulator of heat pain sensitivity. These findings suggest that TRPV1 expressed in dermal and epidermal populations of nociceptors serves as first line defense against heat injury.
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Liberati G, Algoet M, Klöcker A, Ferrao Santos S, Ribeiro-Vaz JG, Raftopoulos C, Mouraux A. Habituation of phase-locked local field potentials and gamma-band oscillations recorded from the human insula. Sci Rep 2018; 8:8265. [PMID: 29844373 PMCID: PMC5974133 DOI: 10.1038/s41598-018-26604-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 05/15/2018] [Indexed: 01/18/2023] Open
Abstract
Salient nociceptive and non-nociceptive stimuli elicit low-frequency local field potentials (LFPs) in the human insula. Nociceptive stimuli also elicit insular gamma-band oscillations (GBOs), possibly preferential for thermonociception, which have been suggested to reflect the intensity of perceived pain. To shed light on the functional significance of these two responses, we investigated whether they would be modulated by stimulation intensity and temporal expectation - two factors contributing to stimulus saliency. Insular activity was recorded from 8 depth electrodes (41 contacts) implanted in the left insula of 6 patients investigated for epilepsy. Thermonociceptive, vibrotactile, and auditory stimuli were delivered using two intensities. To investigate the effects of temporal expectation, the stimuli were delivered in trains of three identical stimuli (S1-S2-S3) separated by a constant 1-s interval. Stimulation intensity affected intensity of perception, the magnitude of low-frequency LFPs, and the magnitude of nociceptive GBOs. Stimulus repetition did not affect perception. In contrast, both low-frequency LFPs and nociceptive GBOs showed a marked habituation of the responses to S2 and S3 as compared to S1 and, hence, a dissociation with intensity of perception. Most importantly, although insular nociceptive GBOs appear to be preferential for thermonociception, they cannot be considered as a correlate of perceived pain.
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Affiliation(s)
- Giulia Liberati
- Institute of Neuroscience, Université catholique de Louvain, 1200, Brussels, Belgium.
| | - Maxime Algoet
- Institute of Neuroscience, Université catholique de Louvain, 1200, Brussels, Belgium
| | - Anne Klöcker
- Institute of Neuroscience, Université catholique de Louvain, 1200, Brussels, Belgium
| | | | | | | | - André Mouraux
- Institute of Neuroscience, Université catholique de Louvain, 1200, Brussels, Belgium
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Not an Aspirin: No Evidence for Acute Anti-Nociception to Laser-Evoked Pain After Motor Cortex rTMS in Healthy Humans. Brain Stimul 2016; 9:48-57. [DOI: 10.1016/j.brs.2015.08.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 08/18/2015] [Accepted: 08/28/2015] [Indexed: 02/06/2023] Open
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Madsen CS, Finnerup NB, Baumgärtner U. Assessment of small fibers using evoked potentials. Scand J Pain 2014; 5:111-118. [DOI: 10.1016/j.sjpain.2013.11.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Accepted: 11/16/2013] [Indexed: 01/08/2023]
Abstract
Abstract
Background and purpose
Conventional neurophysiological techniques do not assess the function of nociceptive pathways and are inadequate to detect abnormalities in patients with small-fiber damage. This overview aims to give an update on the methods and techniques used to assess small fiber (Aδ- and C-fibers) function using evoked potentials in research and clinical settings.
Methods
Noxious radiant or contact heat allows the recording of heat-evoked brain potentials commonly referred to as laser evoked potentials (LEPs) and contact heat-evoked potentials (CHEPs). Both methods reliably assess the loss of Aδ-fiber function by means of reduced amplitude and increased latency of late responses, whereas other methods have been developed to record ultra-late C-fiber-related potentials. Methodological considerations with the use of LEPs and CHEPs include fixed versus variable stimulation site, application pressure, and attentional factors. While the amplitude of LEPs and CHEPs often correlates with the reported intensity of the stimulation, these factors may also be dissociated. It is suggested that the magnitude of the response may be related to the saliency of the noxious stimulus (the ability of the stimulus to stand out from the background) rather than the pain perception.
Results
LEPs and CHEPs are increasingly used as objective laboratory tests to assess the pathways mediating thermal pain, but new methods have recently been developed to evaluate other small-fiber pathways. Pain-related electrically evoked potentials with a low-intensity electrical simulation have been proposed as an alternative method to selectively activate Aδ-nociceptors. A new technique using a flat tip mechanical stimulator has been shown to elicit brain potentials following activation of Type I A mechano-heat (AMH) fibers. These pinprick-evoked potentials (PEP) have a morphology resembling those of heat-evoked potentials following activation of Type II AMH fibers, but with a shorter latency. Cool-evoked potentials can be used for recording the non-nociceptive pathways for cooling. At present, the use of cool-evoked potentials is still in the experimental state. Contact thermodes designed to generate steep heat ramps may be programmed differently to generate cool ramps from a baseline of 35◦C down to 32◦C or 30◦C. Small-fiber evoked potentials are valuable tools for assessment of small-fiber function in sensory neuropathy, central nervous system lesion, and for the diagnosis of neuropathic pain. Recent studies suggest that both CHEPs and pinprick-evoked potentials may also be convenient tools to assess sensitization of the nociceptive system.
Conclusions
In future studies, small-fiber evoked potentials may also be used in studies that aim to understand pain mechanisms including different neuropathic pain phenotypes, such as cold- or touch-evoked allodynia, and to identify predictors of response to pharmacological pain treatment.
Implications
Future studies are needed for some of the newly developed methods.
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Affiliation(s)
- Caspar Skau Madsen
- Danish Pain Research Center , Aarhus University Hospital , Aarhus , Denmark
| | | | - Ulf Baumgärtner
- Department of Neurophysiology, Center for Biomedicine and Medical Technology Mannheim (CBTM) , Heidelberg University , Mannheim , Germany
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The respiratory cycle modulates brain potentials, sympathetic activity, and subjective pain sensation induced by noxious stimulation. Neurosci Res 2014; 84:47-59. [PMID: 24667456 DOI: 10.1016/j.neures.2014.03.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 03/12/2014] [Accepted: 03/13/2014] [Indexed: 12/30/2022]
Abstract
To test the hypothesis that a respiratory cycle influences pain processing, we conducted an experimental pain study in 10 healthy volunteers. Intraepidermal electrical stimulation (IES) with a concentric bipolar needle electrode was applied to the hand dorsum at pain perceptual threshold or four times the perceptual threshold to produce first pain during expiration or inspiration either of which was determined by the abrupt change in an exhaled CO2 level. IES-evoked potentials (IESEPs), sympathetic skin response (SSR), digital plethysmogram (DPG), and subjective pain intensity rating scale were simultaneously recorded. With either stimulus intensity, IES during expiration produced weaker pain feeling compared to IES during inspiration. The mean amplitude of N200/P400 in IESEPs and that of SSR were smaller when IES was applied during expiration. The magnitude of DPG wave gradually decreased after IES, but a decrease in the magnitude of DPG wave was less evident when IES was delivered during expiration. Regardless of stimulus timing or stimulus intensity, pain perception was always concomitant with appearance of IESEPs and SSR, and changes in DPG. Our findings suggest that pain processing fluctuates during normal breathing and that pain is gated within the central nervous system during expiration.
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7
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Pazzaglia C, Valeriani M. Brain-evoked potentials as a tool for diagnosing neuropathic pain. Expert Rev Neurother 2014; 9:759-71. [DOI: 10.1586/ern.09.16] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Predictability of painful stimulation modulates the somatosensory-evoked potential in the rat. PLoS One 2013; 8:e61487. [PMID: 23613862 PMCID: PMC3629015 DOI: 10.1371/journal.pone.0061487] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 03/13/2013] [Indexed: 11/29/2022] Open
Abstract
Somatosensory-evoked potentials (SEPs) are used in humans and animals to increase knowledge about nociception and pain. Since the SEP in humans increases when noxious stimuli are administered unpredictably, predictability potentially influences the SEP in animals as well. To assess the effect of predictability on the SEP in animals, classical fear conditioning was applied to compare SEPs between rats receiving SEP-evoking electrical stimuli either predictably or unpredictably. As in humans, the rat’s SEP increased when SEP-evoking stimuli were administered unpredictably. These data support the hypothesis that the predictability of noxious stimuli plays a distinctive role in the processing of these stimuli in animals. The influence of predictability should be considered when studying nociception and pain in animals. Additionally, this finding suggests that animals confronted with (un)predictable noxious stimuli can be used to investigate the mechanisms underlying the influence of predictability on central processing of noxious stimuli.
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Hu L, Zhao C, Li H, Valentini E. Mismatch responses evoked by nociceptive stimuli. Psychophysiology 2012; 50:158-73. [DOI: 10.1111/psyp.12000] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Accepted: 10/11/2012] [Indexed: 12/29/2022]
Affiliation(s)
- Li Hu
- Key Laboratory of Cognition and Personality (Ministry of Education) and School of Psychology; Southwest University; Chongqing; China
| | - Chen Zhao
- Key Laboratory of Cognition and Personality (Ministry of Education) and School of Psychology; Southwest University; Chongqing; China
| | - Hong Li
- Research Center of Psychological Development and Education; Liaoning Normal University; Liaoning; China
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Gamma-band oscillations in the primary somatosensory cortex--a direct and obligatory correlate of subjective pain intensity. J Neurosci 2012; 32:7429-38. [PMID: 22649223 DOI: 10.1523/jneurosci.5877-11.2012] [Citation(s) in RCA: 217] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Electroencephalographic gamma band oscillations (GBOs) induced over the human primary somatosensory cortex (SI) by nociceptive stimuli have been hypothesized to reflect cortical processing involved directly in pain perception, because their magnitude correlates with pain intensity. However, as stimuli perceived as more painful are also more salient, an alternative interpretation of this correlation is that GBOs reflect unspecific stimulus-triggered attentional processing. In fact, this is suggested by recent observations that other features of the electroencephalographic (EEG) response correlate with pain perception when stimuli are presented in isolation, but not when their saliency is reduced by repetition. Here, by delivering trains of three nociceptive stimuli at a constant 1 s interval, and using different energies to elicit graded pain intensities, we demonstrate that GBOs recorded over SI always predict the subjective pain intensity, even when saliency is reduced by repetition. These results provide evidence for a close relationship between GBOs and the cortical activity subserving pain perception.
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12
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Liu CC, Ohara S, Franaszczuk PJ, Crone NE, Lenz FA. Attention to painful cutaneous laser stimuli evokes directed functional interactions between human sensory and modulatory pain-related cortical areas. Pain 2011; 152:2781-2791. [PMID: 22033363 PMCID: PMC3433227 DOI: 10.1016/j.pain.2011.09.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 08/25/2011] [Accepted: 09/01/2011] [Indexed: 12/30/2022]
Abstract
The human 'pain network' includes cortical areas that are activated during the response to painful stimuli (termed category 1) or during psychological processes that modulate pain, for example, distraction (termed category 2). These categories include parts of the parasylvian (PS), medial frontal (MF), and paracentral cortex (S1&M1). Here we test the hypothesis that causal interactions both within and between category 1 and category 2 modules occur during attention to a painful stimulus. Event-related causality (ERC) was calculated from local field potentials recorded directly from these cortical areas during the response to a painful cutaneous laser stimulus in patients being monitored for epilepsy. The number of electrodes involved in pairs with significant ERC in category 1 was greater for pre-stimulus vs post-stimulus and for attention vs distraction. This is consistent with our prior evidence that the category 1 'pain network' changes rapidly with time intervals and tasks. In contrast, the interaction between categories was often unchanged or stable across intervals and tasks, particularly in MF. The proportion of contacts involved in interactions with PS was greater during distraction vs attention while activation was less, which suggests that distraction involves an inhibitory process in PS. Functional interactions between categories were overwhelmingly in the direction from category 2>1, particularly for contacts in MF which often had a driver role. These results demonstrate that MF is densely interconnected throughout the 'pain network' so that stimulation of MF might be used to disrupt the 'pain network' as a therapy for pain.
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Affiliation(s)
- Chang-Chia Liu
- Department of Neurosurgery, Johns Hopkins University, Baltimore, Maryland, USA Department of Neurology, Johns Hopkins University, Baltimore, Maryland, USA
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Valentini E. The role of perceptual expectation on repetition suppression: a quest to dissect the differential contribution of probability of occurrence and event predictability. Front Hum Neurosci 2011; 5:143. [PMID: 22125520 PMCID: PMC3221400 DOI: 10.3389/fnhum.2011.00143] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 11/02/2011] [Indexed: 11/13/2022] Open
Affiliation(s)
- Elia Valentini
- Dipartimento di Psicologia, Sapienza Università di Roma Roma, Italy
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Valentini E, Torta DME, Mouraux A, Iannetti GD. Dishabituation of Laser-evoked EEG Responses: Dissecting the Effect of Certain and Uncertain Changes in Stimulus Modality. J Cogn Neurosci 2011; 23:2822-37. [DOI: 10.1162/jocn.2011.21609] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Abstract
The repetition of nociceptive stimuli of identical modality, intensity, and location at short and constant interstimulus intervals (ISIs) determines a strong habituation of the corresponding EEG responses, without affecting the subjective perception of pain. To understand what determines this response habituation, we (i) examined the effect of introducing a change in the modality of the repeated stimulus, and (ii) dissected the relative contribution of bottom–up, stimulus-driven changes in modality and top–down, cognitive expectations of such a change, on both laser-evoked and auditory-evoked EEG responses. Multichannel EEG was recorded while participants received trains of three stimuli (S1–S2–S3, a triplet) delivered to the hand dorsum at 1-sec ISI. S3 belonged either to the same modality as S1 and S2 or to the other modality. In addition, participants were either explicitly informed or not informed of the modality of S3. We found that introducing a change in stimulus modality produced a significant dishabituation of the laser-evoked N1, N2, and P2 waves; the auditory N1 and P2 waves; and the laser- and auditory-induced event-related synchronization and desynchronization. In contrast, the lack of explicit knowledge of a possible change in the sensory modality of the stimulus (i.e., uncertainty) only increased the ascending portion of the laser-evoked and auditory-evoked P2 wave. Altogether, these results indicate that bottom–up novelty resulting from the change of stimulus modality, and not top–down cognitive expectations, plays a major role in determining the habituation of these brain responses.
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Affiliation(s)
| | | | - André Mouraux
- 3Universitè Catholique de Louvain, Brussels, Belgium
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15
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Liu CC, Ohara S, Franaszczuk PJ, Lenz FA. Attention to painful cutaneous laser stimuli evokes directed functional connectivity between activity recorded directly from human pain-related cortical structures. Pain 2011; 152:664-675. [PMID: 21255929 PMCID: PMC3043083 DOI: 10.1016/j.pain.2010.12.016] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 12/10/2010] [Accepted: 12/10/2010] [Indexed: 01/14/2023]
Abstract
Our previous studies show that attention to painful cutaneous laser stimuli is associated with functional connectivity between human primary somatosensory cortex (SI), parasylvian cortex (PS), and medial frontal cortex (MF), which may constitute a pain network. However, the direction of functional connections within this network is unknown. We now test the hypothesis that activity recorded from the SI has a driver role, and a causal influence, with respect to activity recorded from PS and MF during attention to a laser. Local field potentials (LFP) were recorded from subdural grid electrodes implanted for the treatment of epilepsy. We estimated causal influences by using the Granger causality (GRC), which was computed while subjects performed either an attention task (counting laser stimuli) or a distraction task (reading for comprehension). Before the laser stimuli, directed attention to the painful stimulus (counting) consistently increased the number of GRC pairs both within the SI cortex and from SI upon PS (SI>PS). After the laser stimulus, attention to a painful stimulus increased the number of GRC pairs from SI>PS, and SI>MF, and within the SI area. LFP at some electrode sites (critical sites) exerted GRC influences upon signals at multiple widespread electrodes, both in other cortical areas and within the area where the critical site was located. Critical sites may bind these areas together into a pain network, and disruption of that network by stimulation at critical sites might be used to treat pain. Electrical activity recorded from the somatosensory cortex drives activity recorded elsewhere in the pain network and may bind the network together; disruption of that network by stimulation at critical sites might be used to treat pain.
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Affiliation(s)
- C-C Liu
- Department of Neurosurgery, Johns Hopkins University, Baltimore, MD, USA Department of Neurology, Johns Hopkins University, Baltimore, MD, USA
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On the selective activation of unmyelinated C-fibers using sinusoidal electrical stimulation: an ERP study. Clin Neurophysiol 2011; 122:1042-7. [PMID: 21353630 DOI: 10.1016/j.clinph.2011.01.046] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 01/07/2011] [Accepted: 01/31/2011] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To verify the possibility of selective activation of C-fibers by a 5-Hz transcutaneous electrical stimulus. METHODS Because Aβ-, Aδ- and C-fibers have different conduction velocities, we verified the selective activation of A- and C-fibers on the basis of evoked potential latencies. We tested whether a 5-Hz sinusoidal electric stimulus could selectively activate C-fibers and consequently generate ultra-late N2/P2 components in the 750-1200 ms range. RESULTS We found that a 5-Hz sine wave stimulus, whether of high or low intensity, elicited N2/P2 complexes only in the late latencies (160-390 ms), suggesting that A-fibers were concomitantly activated along with C-fibers. CONCLUSIONS These findings are in agreement with those of previous simulation studies suggesting that activation of fibers of diameter less than 2.5 μm (i.e., C-fibers) at the 5-Hz frequency requires accompanying activity from Aβ- and Aδ-fibers. SIGNIFICANCE Transcutaneous electrical stimulation with sine wave currents of different frequencies does not seem to be a reliable method for the selective assessment of somatosensory pathways.
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Maarrawi J, Mertens P, Peyron R, Garcia-Larrea L, Sindou M. Functional exploration for neuropathic pain. Adv Tech Stand Neurosurg 2011:25-63. [PMID: 21997740 DOI: 10.1007/978-3-7091-0673-0_2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Neuropathic pain (NP) may become refractory to conservative medical management, necessitating neurosurgical procedures in carefully selected cases. In this context, the functional neurosurgeon must have suitable knowledge of the disease he or she intends to treat, especially its pathophysiology. This latter factor has been studied thanks to advances in the functional exploration of NP, which will be detailed in this review. The study of the flexion reflex is a useful tool for clinical and pharmacological pain assessment and for exploring the mechanisms of pain at multiple levels. The main use of evoked potentials is to confirm clinical, or detect subclinical, dysfunction in peripheral and central somato-sensory pain pathways. LEP and SEP techniques are especially useful when used in combination, allowing the exploration of both pain and somato-sensory pathways. PET scans and fMRI documented rCBF increases to noxious stimuli. In patients with chronic NP, a decreased resting rCBF is observed in the contralateral thalamus, which may be reversed using analgesic procedures. Abnormal pain evoked by innocuous stimuli (allodynia) has been associated with amplification of the thalamic, insular and SII responses, concomitant to a paradoxical CBF decrease in ACC. Multiple PET studies showed that endogenous opioid secretion is very likely to occur as a reaction to pain. In addition, brain opioid receptors (OR) remain relatively untouched in peripheral NP, while a loss of ORs is most likely to occur in central NP, within the medial nociceptive pathways. PET receptor studies have also proved that antalgic Motor Cortex Stimulation (MCS), indicated in severe refractory NP, induces endogenous opioid secretion in key areas of the endogenous opioid system, which may explain one of the mechanisms of action of this procedure, since the secretion is proportional to the analgesic effect.
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Affiliation(s)
- J Maarrawi
- (Faculty of Medicine) and Hôtel-Dieu de France Hospital (Department of Neurosurgery), St Joseph University, Beirut, Lebanon
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Legrain V, Iannetti GD, Plaghki L, Mouraux A. The pain matrix reloaded: a salience detection system for the body. Prog Neurobiol 2010; 93:111-24. [PMID: 21040755 DOI: 10.1016/j.pneurobio.2010.10.005] [Citation(s) in RCA: 580] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2010] [Revised: 10/08/2010] [Accepted: 10/20/2010] [Indexed: 01/18/2023]
Abstract
Neuroimaging and neurophysiological studies have shown that nociceptive stimuli elicit responses in an extensive cortical network including somatosensory, insular and cingulate areas, as well as frontal and parietal areas. This network, often referred to as the "pain matrix", is viewed as representing the activity by which the intensity and unpleasantness of the perception elicited by a nociceptive stimulus are represented. However, recent experiments have reported (i) that pain intensity can be dissociated from the magnitude of responses in the "pain matrix", (ii) that the responses in the "pain matrix" are strongly influenced by the context within which the nociceptive stimuli appear, and (iii) that non-nociceptive stimuli can elicit cortical responses with a spatial configuration similar to that of the "pain matrix". For these reasons, we propose an alternative view of the functional significance of this cortical network, in which it reflects a system involved in detecting, orienting attention towards, and reacting to the occurrence of salient sensory events. This cortical network might represent a basic mechanism through which significant events for the body's integrity are detected, regardless of the sensory channel through which these events are conveyed. This function would involve the construction of a multimodal cortical representation of the body and nearby space. Under the assumption that this network acts as a defensive system signaling potentially damaging threats for the body, emphasis is no longer on the quality of the sensation elicited by noxious stimuli but on the action prompted by the occurrence of potential threats.
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Affiliation(s)
- Valéry Legrain
- Department of Experimental-Clinical and Health Psychology, Ghent University, Belgium.
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19
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Wang AL, Mouraux A, Liang M, Iannetti GD. Stimulus Novelty, and Not Neural Refractoriness, Explains the Repetition Suppression of Laser-Evoked Potentials. J Neurophysiol 2010; 104:2116-24. [DOI: 10.1152/jn.01088.2009] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Brief radiant laser pulses selectively activate skin nociceptors and elicit transient brain responses (laser-evoked potentials [LEPs]). When LEPs are elicited by pairs of stimuli (S1–S2) delivered at different interstimulus intervals (ISIs), the S2-LEP is strongly reduced at short ISIs (250 ms) and progressively recovers at longer ISIs (2,000 ms). This finding has been interpreted in terms of order of arrival of nociceptive volleys and refractoriness of neural generators of LEPs. However, an alternative explanation is the modulation of another experimental factor: the novelty of the eliciting stimulus. To test this alternative hypothesis, we recorded LEPs elicited by pairs of nociceptive stimuli delivered at four ISIs (250, 500, 1,000, 2,000 ms), using two different conditions. In the constant condition, the ISI was identical across the trials of each block, whereas in the variable condition, the ISI was varied randomly across trials and single-stimulus trials were intermixed with paired trials. Therefore the time of occurrence of S2 was both less novel and more predictable in the constant than in the variable condition. In the constant condition, we observed a significant ISI-dependent suppression of the biphasic negative–positive wave (N2–P2) complex of the S2-LEP. In contrast, in the variable condition, the S2-LEP was completely unaffected by stimulus repetition. The pain ratings elicited by S2 were not different in the two conditions. These results indicate that the repetition-suppression of the S2-LEP is not due to refractoriness in nociceptive afferent pathways, but to a modulation of novelty and/or temporal predictability of the eliciting stimulus. This provides further support to the notion that stimulus saliency constitutes a crucial determinant of LEP magnitude and that a significant fraction of the brain activity time-locked to a brief and transient sensory stimulus is not directly related to the quality and the intensity of the corresponding sensation, but to bottom-up attentional processes.
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Affiliation(s)
- A. L. Wang
- Department of Neuroscience, Physiology and Pharmacology, University College London, London
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom; and
| | - A. Mouraux
- Institute of Neurosciences, Université Catholique de Louvain, Louvan, Belgium
| | - M. Liang
- Department of Neuroscience, Physiology and Pharmacology, University College London, London
| | - G. D. Iannetti
- Department of Neuroscience, Physiology and Pharmacology, University College London, London
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom; and
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20
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Iannetti GD, Mouraux A. From the neuromatrix to the pain matrix (and back). Exp Brain Res 2010; 205:1-12. [PMID: 20607220 DOI: 10.1007/s00221-010-2340-1] [Citation(s) in RCA: 383] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2010] [Accepted: 06/14/2010] [Indexed: 12/29/2022]
Abstract
Pain is a conscious experience, crucial for survival. To investigate the neural basis of pain perception in humans, a large number of investigators apply noxious stimuli to the body of volunteers while sampling brain activity using different functional neuroimaging techniques. These responses have been shown to originate from an extensive network of brain regions, which has been christened the Pain Matrix and is often considered to represent a unique cerebral signature for pain perception. As a consequence, the Pain Matrix is often used to understand the neural mechanisms of pain in health and disease. Because the interpretation of a great number of experimental studies relies on the assumption that the brain responses elicited by nociceptive stimuli reflect the activity of a cortical network that is at least partially specific for pain, it appears crucial to ascertain whether this notion is supported by unequivocal experimental evidence. Here, we will review the original concept of the "Neuromatrix" as it was initially proposed by Melzack and its subsequent transformation into a pain-specific matrix. Through a critical discussion of the evidence in favor and against this concept of pain specificity, we show that the fraction of the neuronal activity measured using currently available macroscopic functional neuroimaging techniques (e.g., EEG, MEG, fMRI, PET) in response to transient nociceptive stimulation is likely to be largely unspecific for nociception.
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Affiliation(s)
- G D Iannetti
- Department of Neuroscience, Physiology and Pharmacology, University College London, Medical Sciences Building, Gower Street, London, WC1E 6BT, UK.
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21
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Wang AL, Mouraux A, Liang M, Iannetti GD. The enhancement of the N1 wave elicited by sensory stimuli presented at very short inter-stimulus intervals is a general feature across sensory systems. PLoS One 2008; 3:e3929. [PMID: 19081790 PMCID: PMC2597742 DOI: 10.1371/journal.pone.0003929] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Accepted: 11/16/2008] [Indexed: 01/14/2023] Open
Abstract
Background A paradoxical enhancement of the magnitude of the N1 wave of the auditory event-related potential (ERP) has been described when auditory stimuli are presented at very short (<400 ms) inter-stimulus intervals (ISI). Here, we examined whether this enhancement is specific for the auditory system, or whether it also affects ERPs elicited by stimuli belonging to other sensory modalities. Methodology and Principal Findings We recorded ERPs elicited by auditory and somatosensory stimuli in 13 healthy subjects. For each sensory modality, 4800 stimuli were presented. Auditory stimuli consisted in brief tones presented binaurally, and somatosensory stimuli consisted in constant-current electrical pulses applied to the right median nerve. Stimuli were delivered continuously, and the ISI was varied randomly between 100 and 1000 ms. We found that the ISI had a similar effect on both auditory and somatosensory ERPs. In both sensory modalities, ISI had an opposite effect on the magnitude of the N1 and P2 waves: the magnitude of the auditory and the somatosensory N1 was significantly increased at ISI≤200 ms, while the magnitude of the auditory and the somatosensory P2 was significantly decreased at ISI≤200 ms. Conclusion and Significance The observation that both the auditory and the somatosensory N1 are enhanced at short ISIs indicates that this phenomenon reflects a physiological property that is common across sensory systems, rather than, as previously suggested, unique for the auditory system. Two of the hypotheses most frequently put forward to explain this observation, namely (i) the decreased contribution of inhibitory postsynaptic potentials to the recorded scalp ERPs and (ii) the decreased contribution of ‘latent inhibition’, are discussed. Because neither of these two hypotheses can satisfactorily account for the concomitant reduction of the auditory and the somatosensory P2, we propose a third, novel hypothesis, consisting in the modulation of a single neural component contributing to both the N1 and the P2 waves.
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Affiliation(s)
- An Li Wang
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - André Mouraux
- Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, United Kingdom
- * E-mail:
| | - Meng Liang
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Gian Domenico Iannetti
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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22
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Iannetti GD, Hughes NP, Lee MC, Mouraux A. Determinants of laser-evoked EEG responses: pain perception or stimulus saliency? J Neurophysiol 2008; 100:815-28. [PMID: 18525021 PMCID: PMC2525705 DOI: 10.1152/jn.00097.2008] [Citation(s) in RCA: 288] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Accepted: 05/31/2008] [Indexed: 11/22/2022] Open
Abstract
Although laser-evoked electroencephalographic (EEG) responses are increasingly used to investigate nociceptive pathways, their functional significance remains unclear. The reproducible observation of a robust correlation between the intensity of pain perception and the magnitude of the laser-evoked N1, N2, and P2 responses has led some investigators to consider these responses a direct correlate of the neural activity responsible for pain intensity coding in the human cortex. Here, we provide compelling evidence to the contrary. By delivering trains of three identical laser pulses at four different energies, we explored the modulation exerted by the temporal expectancy of the stimulus on the relationship between intensity of pain perception and magnitude of the following laser-evoked brain responses: the phase-locked N1, N2, and P2 waves, and the non-phase-locked laser-induced synchronization (ERS) and desynchronization (ERD). We showed that increasing the temporal expectancy of the stimulus through stimulus repetition at a constant interstimulus interval 1) significantly reduces the magnitudes of the laser-evoked N1, N2, P2, and ERS; and 2) disrupts the relationship between the intensity of pain perception and the magnitude of these responses. Taken together, our results indicate that laser-evoked EEG responses are not determined by the perception of pain per se, but are mainly determined by the saliency of the eliciting nociceptive stimulus (i.e., its ability to capture attention). Therefore laser-evoked EEG responses represent an indirect readout of the function of the nociceptive system.
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Affiliation(s)
- G D Iannetti
- Department of Physiology, Anatomy, and Genetics, University of Oxford, South Parks Road, OX1 3QX, Oxford, UK.
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23
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Mouraux A, Iannetti GD. A review of the evidence against the “first come first served” hypothesis. Comment on Truini et al. [Pain 2007;131:43–7]. Pain 2008; 136:219-21; author reply 222-3. [DOI: 10.1016/j.pain.2008.02.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2007] [Revised: 01/28/2008] [Accepted: 02/04/2008] [Indexed: 10/22/2022]
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An inhibitory interaction of human cortical responses to stimuli preferentially exciting Adelta or C fibers. Neuroscience 2007; 152:798-808. [PMID: 18308475 DOI: 10.1016/j.neuroscience.2007.11.050] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2007] [Revised: 11/09/2007] [Accepted: 12/01/2007] [Indexed: 12/19/2022]
Abstract
Finely myelinated (type Adelta) and unmyelinated (type C) fibers are the major afferent inputs to spinothalamic tract neurons mediating sensory and reflex responses to noxious and thermal stimuli. These two fiber types differ in their sensory and biophysical properties, raising questions about the interaction of their supraspinal responses. Therefore, we investigated the interaction of cortical responses to stimuli that preferentially excite these fibers in human subjects using evoked potential recordings in a paired conditioning stimulation (CS) and test stimulation (TS) paradigm. There were two experiments, one with Adelta as CS and C as TS (Adelta-C) and another with these stimuli reversed (C-Adelta). We used intra-epidermal electrical pulses applied to the dorsal left hand at 2x and 1x pinprick threshold (pp) for the preferential stimulation of Adelta fibers and 37-50 degrees C contact heat pulses applied to the left or right thenar and left hypothenar eminences for the preferential stimulation of C fibers. We found that the cortical response to preferential Adelta or C fiber stimulation was attenuated whenever either cortical response preceded the other. Standardized values of peak and integrated amplitudes were <1 in all pairing conditions and in all subjects in both experiments. The suppressive effect varied in magnitude with the intensity of the conditioning stimulus in both Adelta-C and C-Adelta experiments. Furthermore, intra-segmental interaction was differentially effective for Adelta conditioning (peak amplitude, P<0.008; analysis of variance). Our experiments provide the first neurophysiological evidence for a somatotopically distributed, mutually suppressive interaction between cortical responses to preferentially activated Adelta and C afferents in humans. This suppressive interaction of cortical responses suggests contrasting and possibly mutually exclusive sensorimotor functions mediated through the Adelta and C fiber afferent channels.
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25
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Mouraux A, Plaghki L. Cortical interactions and integration of nociceptive and non-nociceptive somatosensory inputs in humans. Neuroscience 2007; 150:72-81. [DOI: 10.1016/j.neuroscience.2007.08.035] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2007] [Revised: 08/16/2007] [Accepted: 08/27/2007] [Indexed: 11/25/2022]
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Truini A, Galeotti F, Cruccu G, Garcia-Larrea L. Inhibition of cortical responses to Aδ inputs by a preceding C-related response: Testing the “first come, first served” hypothesis of cortical laser evoked potentials. Pain 2007; 131:341-347. [PMID: 17709206 DOI: 10.1016/j.pain.2007.06.023] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2007] [Revised: 06/14/2007] [Accepted: 06/20/2007] [Indexed: 11/25/2022]
Abstract
Although laser pulses activate concomitantly Adelta and C fibres, the corresponding brain evoked responses remain strictly limited to the Adelta component, without any potential consistent with C-fibre activation. To investigate whether this phenomenon depends on the order of arrival to the cortex ("first come first served" hypothesis) or is simply explained by A-to-C inhibition and/or lower energy associated with the desynchronised C-fibre input, we devised an experiment where the physiological order of arrival to the cortex was artificially inverted. Following a conditioning C-pulse, the cortical response to a second laser stimulus was significantly attenuated, whether it was Adelta or C. Thus, a C-volley was able to depress the response to a subsequent Adelta stimulus, in support of the "first come first served" hypothesis. However, the conditioning C-fibre stimulus attenuated significantly more a subsequent C-volley than a subsequent Adelta-volley, indicating that the suppression effect does not depend solely on the order of arrival to the cortex, but also on the ratio of energy per unit time conveyed by the successive inputs. This supports the notion that cortical evoked potentials to laser pulses (and probably to other sensory stimuli) reflect networks detecting rapid energy changes relative to a preceding baseline. The output of such networks should depend both on the time elapsed between successive inputs and on the relative energy per unit time conveyed by successive volleys. Such dedicated networks aimed at detecting energy changes may be related to orienting reactions, and can be dissociated from subjective perception.
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Affiliation(s)
- A Truini
- Department of Neurological Sciences, University La Sapienza, Rome, Italy INSERM Unit U879 "Central Integration of Pain", University Lyon 1, France
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27
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Schestatsky P, Algaba R, Pérez D, Casanova-Molla J, León L, Costa J, Valls-Solé J. Transient decrease of sensory perception after thermoalgesic stimuli for quantitative sensory testing. Muscle Nerve 2007; 36:466-70. [PMID: 17621355 DOI: 10.1002/mus.20837] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Transient decrease in the excitability of a reflex circuit following its activation by appropriate stimuli is a well-recognized phenomenon, but it is unclear how this applies to thermoalgesic stimuli during quantitative sensory testing (QST). We examined the effects induced by a thermoalgesic (conditioning) stimulus on the response to a subsequent (test) stimulus of the same characteristics. All tests were done using a Peltier thermode with a surface area of 12.5 cm(2) using ramp rates of 2 degrees C/s and variable interstimulus intervals (ISIs) ranging from 10 to 60 s. Perception was measured with an electronic visual analog scale. No changes were observed in latency of pain perception. However, latency of warm perception was significantly delayed and pain perception intensity was significantly reduced with respect to conditioning stimuli at ISIs below 60 s. Our results indicate a transient saturation of warm and heat pain perception systems after a thermoalgesic stimulus. We therefore recommend that time intervals of >1 min be used between two consecutive thermoalgesic stimuli when examining QST.
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Affiliation(s)
- Pedro Schestatsky
- Department of Neurology, Hospital Clínic, Universitat de Barcelona, Villarroel 170, Barcelona, Spain
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Garcia-Larrea L. Chapter 30 Evoked potentials in the assessment of pain. HANDBOOK OF CLINICAL NEUROLOGY 2006; 81:439-XI. [PMID: 18808852 DOI: 10.1016/s0072-9752(06)80034-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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Mouraux A, Plaghki L. Chapter 27 Are the processes reflected by late and ultra-late laser evoked potentials specific of nociception? SUPPLEMENTS TO CLINICAL NEUROPHYSIOLOGY 2006; 59:197-204. [PMID: 16893112 DOI: 10.1016/s1567-424x(09)70031-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- A Mouraux
- Laboratoire de Neurophysiologie (NEFY), Université Catholique de Louvain, B-1200 Brussels, Belgium.
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30
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Garcia-Larrea L. Somatosensory volleys and cortical evoked potentials: ‘First come, first served’? Pain 2004; 112:5-7. [PMID: 15494177 DOI: 10.1016/j.pain.2004.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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