Journal of Manipulative and Physiological Therapeutics, 2007
Objective: The objective of this study was to develop a measurement method that could be implemen... more Objective: The objective of this study was to develop a measurement method that could be implemented in chiropractic for the evaluation of angular and translational intervertebral motion of the cervical spine.
The anatomy of the somatosensory system allows both serial and parallel information flow but the ... more The anatomy of the somatosensory system allows both serial and parallel information flow but the conditions involving each mode of processing is a matter of debate. In this functional magnetic resonance imaging (fMRI) study, cutaneous electrical stimulation was applied to human volunteers at three intensities (low-innocuous, moderate-noxious and high-noxious) to investigate interactions between contralateral primary and secondary somatosensory cortices (S1c and S2c), and between contralateral and ipsilateral S2 (S2c and S2i), using dynamic causal modeling (DCM). Our results are consistent with serial processing with a key role of the direct input to S1c for all three intensity levels. The more intense stimulus also induced significantly more interactions between S2i and S2c, consistent with an increase in inter-hemispheric integration associated with the additional recruitment of nociceptive inputs. However, stronger pain reports were also associated with reduced information flow fr...
The mechanisms of chronic pain in irritable bowel syndrome (IBS) have been widely investigated bu... more The mechanisms of chronic pain in irritable bowel syndrome (IBS) have been widely investigated but remain unclear. The present study investigated the relation between visceral hypersensitivity, cutaneous thermal sensitivity, and central pain mechanisms. Rectal sensitivity was assessed with a barostat, and forearm and calf sensitivity with a contact thermode. Central mechanisms were assessed by counterirritation using sustained cold-pain to the hand and painful electric shocks to the ankle. Psychological symptoms were also assessed, using questionnaires. Female volunteers with diarrhea-predominant IBS (n = 27) and healthy controls (n = 25) participated in the study. IBS patients had lower rectal and calf pain thresholds compared to controls (p's < 0.05). IBS patients also reported more pain than controls for rectal distensions, and heat pain on the calf and forearm (all p's < 0.001). Cold-pain inhibited shock-pain in controls but not IBS patients (controls: À13.5 ± 5.3 vs IBS: +1.9 ± 10.5; p < 0.01). In addition, visceral hypersensitivity was significantly correlated to cutaneous thermal hypersensitivity and pain inhibition deficits, although effects were only weak and moderate, respectively. Furthermore, covariance analyses indicated that psychological factors accounted for group differences in visceral hypersensitivity and pain inhibition deficits. In conclusion, this study confirms the relation between altered pain inhibition processes and widespread hypersensitivity in IBS. The present results also suggests that psychological symptoms and altered pain processing in IBS patients may reflect at least in part, common underlying mechanisms.
Heterotopic noxious counterstimulation (HNCS) by the application of a sustained noxious stimulus ... more Heterotopic noxious counterstimulation (HNCS) by the application of a sustained noxious stimulus has been shown to inhibit nociceptive processes and decrease pain induced by a competing noxious stimulus. However, it is still not clear how attentional processes contribute to these effects. The main objective of this study was to compare the analgesic effects of HNCS in 2 sessions during which top-down attention was manipulated. Acute shock pain and the nociceptive flexion reflex were evoked by transcutaneous electrical stimulations of the right sural nerve in 4 blocks (15 stimuli/block): baseline, heterotopic innocuous counterstimulation (HICS), HNCS, and recovery. Counterstimulation was applied on the left upper limb with a thermode (HICS) or a cold pack (HNCS). Attention was manipulated between sessions by instructing participants to focus their attention on shock pain or counterstimulation. Shock pain ratings decreased significantly during counterstimulation (P < .001) with stronger effects of HNCS vs HICS in both sessions (P < .01). Furthermore, shock pain inhibition during HNCS relative to baseline was stronger with attention focusing on counterstimulation compared to attention focusing on shocks (P = .015). However, the relative decrease in pain ratings during HNCS vs HICS was not significantly affected by the direction of attention (P = .7). As for spinal nociceptive processes, nociceptive flexion reflex amplitude was significantly decreased during counterstimulation (P < .001) with larger reductions during HNCS compared to HICS (P = .03). However, these effects were not altered by attention (P = .35). Together, these results demonstrate that top-down attention and HNCS produce additive analgesic effects. However, attentional modulation of HNCS analgesia seems to depend on supraspinal processes. Ó
Vascular changes associated with brain functions are thought to be tightly coupled with neuronal ... more Vascular changes associated with brain functions are thought to be tightly coupled with neuronal activity through neuronal glucose consumption or the local release of vasoactive agents. In contrast, another view suggests that cortical blood flow is strongly regulated by the nucleus basalis of Meynert (NBM), independently of regional metabolism. Thus, although cortical regional cerebral blood flow (rCBF) variations induced by somatosensory stimulation are strongly linked to neuronal activity, they may also be partly controlled by the NBM. In the present study, cortical rCBF alterations in response to innocuous brushing of the hindlimb (HL) were investigated by laser speckle contrast imaging. The contribution of NBM to these changes was examined after injection of the GABAergic agonist muscimol into the right NBM, allowing comparison of somatosensory-evoked cortical rCBF modifications before and after NBM inactivation. As expected, HL brushing elicited a robust rCBF increase in the contralateral parietal cortex (PC), over the representation of the HL. However, these alterations were decreased, by approximately 40%, in the hemisphere ipsilateral to muscimol inactivation of NBM, whereas vehicle injection did not produce any significant variation. The results demonstrate that cortical rCBF changes induced by somatosensory stimulation are partly regulated by NBM.
Pain is a complex experience involving extensive interactions between brain and spinal cord proce... more Pain is a complex experience involving extensive interactions between brain and spinal cord processes. Various interventions that modulate pain, such as the application of a competing noxious stimulus (counterirritation), are thought to involve cerebrospinal regulation through diffuse noxious inhibitory controls (DNICs). However, no study has yet examined the relation between brain and spinal cord activity during counterirritation analgesia in humans. This fMRI study investigates brain responses to phasic painful electrical stimulation administered to the sural nerve to evoke a spinal nociceptive response (RIII reflex) before, during and after counterirritation induced by the immersion of the left contralateral foot in cold water. Responses are compared with a control condition without counterirritation. As expected, counterirritation produced robust pain inhibition with residual analgesia persisting during the recovery period. In contrast, RIII reflex amplitude was significantly decreased by counterirritation only in a subset of subjects. Modulatory effects of counterirritation on pain perception and spinal nociception were paralleled by decreased shock-evoked activity in pain-related areas. Individual changes in shock-evoked brain activity were specifically related to analgesia in primary somatosensory cortex (SI), anterior cingulate cortex and amygdala, and to RIII modulation in supplementary motor area and orbitofrontal cortex (OFC). Moreover, sustained activation induced by the counterirritation stimulus in the OFC predicted shock-pain decrease while sustained activity in SI and the periaqueductal gray matter predicted RIII modulation. These results provide evidence for the implication of at least two partly separable neural mechanisms underlying the effects of counterirritation on pain and spinal nociception in humans.
The analgesic effect of heterotopic noxious counter-stimulation (HNCS; ''pain inhibits pain'') ha... more The analgesic effect of heterotopic noxious counter-stimulation (HNCS; ''pain inhibits pain'') has been shown to decrease in older persons, while some neuropsychological studies have suggested a reduction in cognitive inhibition with normal aging. Taken together, these findings may reflect a generalized reduction in inhibitory processes. The present study assessed whether the decline in the efficacy of pain inhibition processes is associated with decreased cognitive inhibition in older persons. Healthy young (18-46 years old; n = 21) and older (56-75 years old; n = 23) adult volunteers participated in one experimental session to assess the effect of HNCS (cold pain applied on the left forearm) on shock pain and RIII reflex induced by transcutaneous electrical stimulation of the right sural nerve. In the same session, participants also performed a modified Stroop task, including a target condition requiring the frequent switching between inhibition and no inhibition of the meaning of color words. The analgesic effect induced by HCNS was significantly smaller in older participants for both shock-pain ratings (P < 0.001) and RIII-reflex amplitude (P < 0.05). The Stroop effect was significantly larger in elderly participants in the inhibition trials of the switching condition. Increased cognitive interference (ie, larger Stroop effect) correlated with smaller inhibition of the RIII reflex by HNCS across groups (r = À.34, P = 0.025). This association was independent from the age-related slowing observed in control reading and naming tasks. These results suggest a generalized age-related reduction in inhibitory processes affecting both executive functions and cerebrospinal processes involved in the regulation of pain-related responses induced by competing nociceptive threats. Ó
Please cite this article in press as: Piché, M., et al., Basal -opioid receptor availability in t... more Please cite this article in press as: Piché, M., et al., Basal -opioid receptor availability in the amygdala predicts the inhibition of pain-related brain activity during heterotopic noxious counter-stimulation. Neurosci. Res. (2014), http://dx.
The voluntary control of respiration is used as a common means to regulate pain and emotions and ... more The voluntary control of respiration is used as a common means to regulate pain and emotions and is fundamental to various relaxation and meditation techniques. The aim of the present study was to examine how breathing frequency and phase affect pain perception, spinal nociceptive activity (RIII-reflex) and brain activity (scalp somatosensoryevoked potentials -SEP's). In 20 healthy volunteers, painful electric shocks individually adjusted to 120% of the RIIIreflex threshold were delivered to the sural nerve near the end of inspiration or expiration phases, during three cuedbreathing conditions: (1) slow breathing (0.1 Hz) with slow (4 s) inspiration (0.1 Hz-SlowIns), (2) slow breathing (0.1 Hz) with fast (2 s) inspiration (0.1 Hz-FastIns), and (3) normal breathing (0.2 Hz) with fast (2 s) inspiration (0.2 Hz). Pain ratings were not affected by breathing patterns (p = 0.3), but were significantly lower during inspiration compared with expiration (p = 0.02). This phase effect was also observed on the N100 component of SEP's, but only in the 0.1-Hz-FastIns condition (p = 0.03). In contrast, RIIIreflex amplitude was greater during inspiration compared with expiration (p = 0.02). It was also decreased in the 0.1-Hz-SlowIns compared with the 0.2-Hz condition (p = 0.01). Slow breathing also increased the amplitude of respiratory sinus arrhythmia (RSA), although these changes were not significantly associated with changes in pain responses.
A number of studies on humans and animals have demonstrated better auditory abilities in blind wi... more A number of studies on humans and animals have demonstrated better auditory abilities in blind with respect to sighted subjects and have tried to define the mechanisms through which this compensation occurs. The aim of the present study, therefore, was to examine the participation of primary visual cortex (V1) to auditory processing in early enucleated rats. Here we show, using gaussian noise bursts, that about a third of the cells in V1 responded to auditory stimulation in blind rats and most of these (78%) had ON-type responses and low spontaneous activity. Moreover, they were distributed throughout visual cortex without any apparent tonotopic organization. Optimal frequencies determined using pure tones were rather high but comparable to those found in auditory cortex of blind and sighted rats. On the other hand, sensory thresholds determined at these frequencies were higher and bandwidths were wider in V1 of the blind animals. Blind and sighted rats were also stimulated for 60 min with gaussian noise, their brains removed and processed for c-Fos immunohistochemistry. Results revealed that c-Fos positive cells were not only present in auditory cortex of both groups of rats but there was a 10-fold increase in labeled cells in V1 and a fivefold increase in secondary visual cortex (V2) of early enucleated rats in comparisons to sighted ones. Also, the pattern of distribution of these labeled cells across layers suggests that the recruitment of V1 could originate at least in part through inputs arising from the thalamus. The ensemble of results appears to indicate that cross-modal compensation leading to improved performance in the blind depends on cell recruitment in V1 but probably also plastic changes in lower-and higher-order visual structures and possibly in the auditory system.
The evaluation of spinal cord neuronal activity in humans with functional magnetic resonance imag... more The evaluation of spinal cord neuronal activity in humans with functional magnetic resonance imaging (fMRI) is technically challenging. Major difficulties arise from cardiac and respiratory movement artifacts that constitute significant sources of noise. In this paper we assessed the Correction of Structured noise using spatial Independent Component Analysis (CORSICA). FMRI data of the cervical spinal cord were acquired in 14 healthy subjects using gradient-echo EPI. Nociceptive electrical stimuli were applied to the thumb. Additional data with short TR (250 ms, to prevent aliasing) were acquired to generate a spatial map of physiological noise derived from Independent Component Analysis (ICA). Physiological noise was subsequently removed from the long-TR data after selecting independent components based on the generated noise map. Stimulus-evoked responses were analyzed using the general linear model, with and without CORSICA and with a regressor generated from the cerebrospinal fluid region. Results showed higher sensitivity to detect stimulus-related activation in the targeted dorsal segment of the cord after CORSICA. Furthermore, fewer voxels showed stimulus-related signal changes in the CSF and outside the spinal region, suggesting an increase in specificity. ICA can be used to effectively reduce physiological noise in spinal cord fMRI time series.
Magnetic resonance imaging (MRI) has recently been applied to study spinal cord function in human... more Magnetic resonance imaging (MRI) has recently been applied to study spinal cord function in humans. However, spinal functional MRI (f MRI) encounters major technical challenges with cardiac noise being considered a major source of noise. The present study relied on echoplanar imaging of the cervical cord at short TR (TR=250 ms; TE=40 ms; flip=45°), combined with plethysmographic recordings to characterize the spatiotemporal properties of cardiac-induced signal changes in spinal f MRI. Frequency-based analyses examining signal change at the cardiac frequency confirmed mean fluctuations of about 10% (relative to the mean signal) in the spinal cord and surrounding cerebrospinal fluid (CSF), with maximal responses reaching up to 66% in some voxels. A spatial independent component analysis (sICA) confirmed that cardiac noise is an important source of variance in spinal f MRI with several components showing a response coherent with the cardiac frequency spectrum. The time course of the main cardiac components approximated a sinusoidal function tightly coupled to the cardiac systole with at least one component showing a comparable temporal profile across runs and subjects. Spatially, both the frequency-domain analysis and the sICA demonstrated cardiac noise distributed irregularly along the full rostrocaudal extent of the segments scanned with peaks concentrated in the ventral part of the lateral slices in all scans and subjects, consistent with the major channels of CSF flow. These results confirm that cardiacinduced changes are a significant source of noise likely to affect the detection of spinal Blood Oxygen Level Dependent (BOLD) responses. Most importantly, the complex spatiotemporal structure of cardiac noise is unlikely to be accounted for adequately by ad hoc linear methods, especially in data acquired using long TR (i.e. aliasing the cardiac frequency). However, the reliable spatiotemporal distribution of cardiac noise across scanning runs and within subjects may provide a valid means to identify and extract cardiac noise based on sICA methods.
Your article is protected by copyright and all rights are held exclusively by The Physiological S... more Your article is protected by copyright and all rights are held exclusively by The Physiological Society of Japan and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Journal of Manipulative and Physiological Therapeutics, 2012
Purpose: The purpose of this study was to investigate the alteration of pain-induced neuromuscula... more Purpose: The purpose of this study was to investigate the alteration of pain-induced neuromuscular trunk responses by expectations in healthy volunteers. Methods: Twenty-three asymptomatic participants performed series of flexion-extension movements in 3 different experimental conditions: innocuous heat stimulation (control) and noxious heat stimulation associated with expectations of low or high pain intensity. These stimuli were administered by a contact thermode placed over the lumbar region (L4 and L5) to assess the modulation of neuromuscular responses and kinematics during the flexionextension task. Surface electromyography (EMG) of lumbar erector spinae at L2 and L3 and L4 and L5 as well as lumbopelvic kinematic variables were compared across conditions. Results: Noxious stimulation significantly altered EMG responses but only in full trunk flexion. Interestingly, this alteration was significant only for muscles where noxious stimulation was applied (L4 and L5) and not for the other segment (L2 and L3). Conversely, expectations significantly altered EMG activity at L2 and L3 but not at the segment where noxious stimulation was applied. Conclusion: These results confirm previous findings and indicate that experimental pain can alter neuromuscular responses during a trunk flexion-extension task. Furthermore, this study suggests that expectations can alter some of these alterations. Future studies should determine whether neuromuscular changes induced by expectations may contribute to the transition from acute to chronic low-back pain. (J Manipulative Physiol Ther 2012;35:636-644)
Studies of electromyographic (EMG) activity and lumbopelvic rhythm have led to a better understan... more Studies of electromyographic (EMG) activity and lumbopelvic rhythm have led to a better understanding of neuromuscular alterations in chronic low back pain (cLBP) patients. Whether these changes reflect adaptations to chronic pain or are induced by acute pain is still unclear. This work aimed to assess the effects of experimental LBP on lumbar erector spinae (LES) EMG activity and lumbopelvic kinematics during a trunk flexion-extension task in healthy volunteers and LBP patients. The contribution of disability to these effects was also examined. Twelve healthy participants and 14 cLBP patients performed flexionextension tasks in three conditions; control, innocuous heat and noxious heat, applied on the skin over L5 or T7. The results indicated that noxious heat at L5 evoked specific increases in LES activity during static full trunk flexion and extension, irrespective of participants' group. Kinematic data suggested that LBP patients adopted a different movement strategy than controls when noxious heat was applied at the L5 level. Besides, high disability was associated with less kinematic changes when approaching and leaving full flexion. These results indicate that experimental pain can induce neuromechanical alterations in cLBP patients and healthy volunteers, and that higher disability in patients is associated with decreased movement pattern changes.
Patients with chronic low back pain exhibit characteristics such as clinical pain, psychological ... more Patients with chronic low back pain exhibit characteristics such as clinical pain, psychological symptoms and neuromuscular adaptations. The purpose of this study was to determine the independent contribution of clinical pain, psychological factors and neuromuscular adaptations to disability in patients with chronic low back pain. Clinical pain intensity, pain catastrophizing, fear-avoidance beliefs, anxiety, neuromuscular adaptations to chronic pain and neuromuscular responses to experimental pain were assessed in 52 patients with chronic low back pain. Lumbar muscle electromyographic activity was assessed during a flexion-extension task (flexion relaxation phenomenon) to assess both chronic neuromuscular adaptations and neuromuscular responses to experimental pain during the task. Multiple regressions showed that independent predictors of disability included neuromuscular adaptations to chronic pain (b = 0.25, p = 0.006, sr 2 = 0.06), neuromuscular responses to experimental pain (b = À0.24, p = 0.011, sr 2 = 0.05), clinical pain intensity (b = 0.28, p = 0.002, sr 2 = 0.08) and psychological factors (b = 0.58, p < 0.001, sr 2 = 0.32). Together, these predictors accounted for 65% of variance in disability (R 2 = 0.65 p < 0.001). The current investigation revealed that neuromuscular adaptations are independent from clinical pain intensity and psychological factors, and contribute to inter-individual differences in patients' disability. This suggests that disability, in chronic low back pain patients, is determined by a combination of factors, including clinical pain, psychological factors and neuromuscular adaptations.
In animals, somatic stimulation of the limbs can evoke sympathetic reflexes of supraspinal origin... more In animals, somatic stimulation of the limbs can evoke sympathetic reflexes of supraspinal origin. In addition, spinal reflexes can be elicited by stimulation of somatic tissues of the trunk. However, limited evidence is available concerning the specific modulation of sympathetic reflexes by afferents from the thoracic spine. This has also been largely overlooked in healthy humans. The aim of the present study was to determine whether tonic noxious heat (NH) applied to the skin over T3-T5 could segmentally increase supraspinal sympathetic reflexes (skin conductance responses - SCRs) induced by phasic electrical stimulation of the sural nerve. In addition, the effect of spinal manipulation (SM) on SCR amplitude and SCR amplification by NH was investigated. During the control session, palmar and plantar SCR amplitude was stable, showing no significant modulation. During NH and SM, however, palmar SCR amplitude was respectively increased and decreased in comparison to baseline, leading...
Enrichment of the environment is an effective means of enhancing neuronal development and plastic... more Enrichment of the environment is an effective means of enhancing neuronal development and plasticity but its effect on the cross-modal compensation resulting from sensory deprivation has never been investigated. The present study used c-Fos immunohistochemistry and dextran-biotin neuronal tracing to examine the reorganization of sensory modalities in the brain of anophthalmic mutant mice (ZRDCT/An) raised in either enriched or standard environments. Auditory stimulation was found to elicit strong neuronal activation in thalamic and cortical structures that are normally visual. An important finding was that the latter auditory-evoked cortical activity was considerably enhanced in blind mice raised in the enriched environment. The axonal tracing study demonstrated auditory inputs from the inferior colliculus to the visual thalamus. This animal model will be useful for understanding neuronal mechanisms underlying some cross-modal sensory phenomena observed in blind or deaf humans.
This study examines the effect of normal aging on temporal summation (TS) of pain and the nocicep... more This study examines the effect of normal aging on temporal summation (TS) of pain and the nociceptive flexion reflex (RIII). Two groups of healthy volunteers, young and elderly, received transcutaneous electrical stimulation applied to the right sural nerve to assess pain and the nociceptive flexion reflex (RIII-reflex). Stimulus intensity was adjusted individually to 120% of RIII-reflex threshold, and shocks were delivered as a single stimulus or as a series of 5 stimuli to assess TS at 5 different frequencies (0.17, 0.33, 0.66, 1, and 2 Hz). This study shows that robust TS of pain and RIII-reflex is observable in individuals aged between 18 and 75 years and indicates that these effects are comparable between young and older individuals. These results contrast with some previous findings and imply that at least some pain regulatory processes, including TS, may not be affected by normal aging, although this may vary depending on the method.
Journal of Manipulative and Physiological Therapeutics, 2007
Objective: The objective of this study was to develop a measurement method that could be implemen... more Objective: The objective of this study was to develop a measurement method that could be implemented in chiropractic for the evaluation of angular and translational intervertebral motion of the cervical spine.
The anatomy of the somatosensory system allows both serial and parallel information flow but the ... more The anatomy of the somatosensory system allows both serial and parallel information flow but the conditions involving each mode of processing is a matter of debate. In this functional magnetic resonance imaging (fMRI) study, cutaneous electrical stimulation was applied to human volunteers at three intensities (low-innocuous, moderate-noxious and high-noxious) to investigate interactions between contralateral primary and secondary somatosensory cortices (S1c and S2c), and between contralateral and ipsilateral S2 (S2c and S2i), using dynamic causal modeling (DCM). Our results are consistent with serial processing with a key role of the direct input to S1c for all three intensity levels. The more intense stimulus also induced significantly more interactions between S2i and S2c, consistent with an increase in inter-hemispheric integration associated with the additional recruitment of nociceptive inputs. However, stronger pain reports were also associated with reduced information flow fr...
The mechanisms of chronic pain in irritable bowel syndrome (IBS) have been widely investigated bu... more The mechanisms of chronic pain in irritable bowel syndrome (IBS) have been widely investigated but remain unclear. The present study investigated the relation between visceral hypersensitivity, cutaneous thermal sensitivity, and central pain mechanisms. Rectal sensitivity was assessed with a barostat, and forearm and calf sensitivity with a contact thermode. Central mechanisms were assessed by counterirritation using sustained cold-pain to the hand and painful electric shocks to the ankle. Psychological symptoms were also assessed, using questionnaires. Female volunteers with diarrhea-predominant IBS (n = 27) and healthy controls (n = 25) participated in the study. IBS patients had lower rectal and calf pain thresholds compared to controls (p's < 0.05). IBS patients also reported more pain than controls for rectal distensions, and heat pain on the calf and forearm (all p's < 0.001). Cold-pain inhibited shock-pain in controls but not IBS patients (controls: À13.5 ± 5.3 vs IBS: +1.9 ± 10.5; p < 0.01). In addition, visceral hypersensitivity was significantly correlated to cutaneous thermal hypersensitivity and pain inhibition deficits, although effects were only weak and moderate, respectively. Furthermore, covariance analyses indicated that psychological factors accounted for group differences in visceral hypersensitivity and pain inhibition deficits. In conclusion, this study confirms the relation between altered pain inhibition processes and widespread hypersensitivity in IBS. The present results also suggests that psychological symptoms and altered pain processing in IBS patients may reflect at least in part, common underlying mechanisms.
Heterotopic noxious counterstimulation (HNCS) by the application of a sustained noxious stimulus ... more Heterotopic noxious counterstimulation (HNCS) by the application of a sustained noxious stimulus has been shown to inhibit nociceptive processes and decrease pain induced by a competing noxious stimulus. However, it is still not clear how attentional processes contribute to these effects. The main objective of this study was to compare the analgesic effects of HNCS in 2 sessions during which top-down attention was manipulated. Acute shock pain and the nociceptive flexion reflex were evoked by transcutaneous electrical stimulations of the right sural nerve in 4 blocks (15 stimuli/block): baseline, heterotopic innocuous counterstimulation (HICS), HNCS, and recovery. Counterstimulation was applied on the left upper limb with a thermode (HICS) or a cold pack (HNCS). Attention was manipulated between sessions by instructing participants to focus their attention on shock pain or counterstimulation. Shock pain ratings decreased significantly during counterstimulation (P < .001) with stronger effects of HNCS vs HICS in both sessions (P < .01). Furthermore, shock pain inhibition during HNCS relative to baseline was stronger with attention focusing on counterstimulation compared to attention focusing on shocks (P = .015). However, the relative decrease in pain ratings during HNCS vs HICS was not significantly affected by the direction of attention (P = .7). As for spinal nociceptive processes, nociceptive flexion reflex amplitude was significantly decreased during counterstimulation (P < .001) with larger reductions during HNCS compared to HICS (P = .03). However, these effects were not altered by attention (P = .35). Together, these results demonstrate that top-down attention and HNCS produce additive analgesic effects. However, attentional modulation of HNCS analgesia seems to depend on supraspinal processes. Ó
Vascular changes associated with brain functions are thought to be tightly coupled with neuronal ... more Vascular changes associated with brain functions are thought to be tightly coupled with neuronal activity through neuronal glucose consumption or the local release of vasoactive agents. In contrast, another view suggests that cortical blood flow is strongly regulated by the nucleus basalis of Meynert (NBM), independently of regional metabolism. Thus, although cortical regional cerebral blood flow (rCBF) variations induced by somatosensory stimulation are strongly linked to neuronal activity, they may also be partly controlled by the NBM. In the present study, cortical rCBF alterations in response to innocuous brushing of the hindlimb (HL) were investigated by laser speckle contrast imaging. The contribution of NBM to these changes was examined after injection of the GABAergic agonist muscimol into the right NBM, allowing comparison of somatosensory-evoked cortical rCBF modifications before and after NBM inactivation. As expected, HL brushing elicited a robust rCBF increase in the contralateral parietal cortex (PC), over the representation of the HL. However, these alterations were decreased, by approximately 40%, in the hemisphere ipsilateral to muscimol inactivation of NBM, whereas vehicle injection did not produce any significant variation. The results demonstrate that cortical rCBF changes induced by somatosensory stimulation are partly regulated by NBM.
Pain is a complex experience involving extensive interactions between brain and spinal cord proce... more Pain is a complex experience involving extensive interactions between brain and spinal cord processes. Various interventions that modulate pain, such as the application of a competing noxious stimulus (counterirritation), are thought to involve cerebrospinal regulation through diffuse noxious inhibitory controls (DNICs). However, no study has yet examined the relation between brain and spinal cord activity during counterirritation analgesia in humans. This fMRI study investigates brain responses to phasic painful electrical stimulation administered to the sural nerve to evoke a spinal nociceptive response (RIII reflex) before, during and after counterirritation induced by the immersion of the left contralateral foot in cold water. Responses are compared with a control condition without counterirritation. As expected, counterirritation produced robust pain inhibition with residual analgesia persisting during the recovery period. In contrast, RIII reflex amplitude was significantly decreased by counterirritation only in a subset of subjects. Modulatory effects of counterirritation on pain perception and spinal nociception were paralleled by decreased shock-evoked activity in pain-related areas. Individual changes in shock-evoked brain activity were specifically related to analgesia in primary somatosensory cortex (SI), anterior cingulate cortex and amygdala, and to RIII modulation in supplementary motor area and orbitofrontal cortex (OFC). Moreover, sustained activation induced by the counterirritation stimulus in the OFC predicted shock-pain decrease while sustained activity in SI and the periaqueductal gray matter predicted RIII modulation. These results provide evidence for the implication of at least two partly separable neural mechanisms underlying the effects of counterirritation on pain and spinal nociception in humans.
The analgesic effect of heterotopic noxious counter-stimulation (HNCS; ''pain inhibits pain'') ha... more The analgesic effect of heterotopic noxious counter-stimulation (HNCS; ''pain inhibits pain'') has been shown to decrease in older persons, while some neuropsychological studies have suggested a reduction in cognitive inhibition with normal aging. Taken together, these findings may reflect a generalized reduction in inhibitory processes. The present study assessed whether the decline in the efficacy of pain inhibition processes is associated with decreased cognitive inhibition in older persons. Healthy young (18-46 years old; n = 21) and older (56-75 years old; n = 23) adult volunteers participated in one experimental session to assess the effect of HNCS (cold pain applied on the left forearm) on shock pain and RIII reflex induced by transcutaneous electrical stimulation of the right sural nerve. In the same session, participants also performed a modified Stroop task, including a target condition requiring the frequent switching between inhibition and no inhibition of the meaning of color words. The analgesic effect induced by HCNS was significantly smaller in older participants for both shock-pain ratings (P < 0.001) and RIII-reflex amplitude (P < 0.05). The Stroop effect was significantly larger in elderly participants in the inhibition trials of the switching condition. Increased cognitive interference (ie, larger Stroop effect) correlated with smaller inhibition of the RIII reflex by HNCS across groups (r = À.34, P = 0.025). This association was independent from the age-related slowing observed in control reading and naming tasks. These results suggest a generalized age-related reduction in inhibitory processes affecting both executive functions and cerebrospinal processes involved in the regulation of pain-related responses induced by competing nociceptive threats. Ó
Please cite this article in press as: Piché, M., et al., Basal -opioid receptor availability in t... more Please cite this article in press as: Piché, M., et al., Basal -opioid receptor availability in the amygdala predicts the inhibition of pain-related brain activity during heterotopic noxious counter-stimulation. Neurosci. Res. (2014), http://dx.
The voluntary control of respiration is used as a common means to regulate pain and emotions and ... more The voluntary control of respiration is used as a common means to regulate pain and emotions and is fundamental to various relaxation and meditation techniques. The aim of the present study was to examine how breathing frequency and phase affect pain perception, spinal nociceptive activity (RIII-reflex) and brain activity (scalp somatosensoryevoked potentials -SEP's). In 20 healthy volunteers, painful electric shocks individually adjusted to 120% of the RIIIreflex threshold were delivered to the sural nerve near the end of inspiration or expiration phases, during three cuedbreathing conditions: (1) slow breathing (0.1 Hz) with slow (4 s) inspiration (0.1 Hz-SlowIns), (2) slow breathing (0.1 Hz) with fast (2 s) inspiration (0.1 Hz-FastIns), and (3) normal breathing (0.2 Hz) with fast (2 s) inspiration (0.2 Hz). Pain ratings were not affected by breathing patterns (p = 0.3), but were significantly lower during inspiration compared with expiration (p = 0.02). This phase effect was also observed on the N100 component of SEP's, but only in the 0.1-Hz-FastIns condition (p = 0.03). In contrast, RIIIreflex amplitude was greater during inspiration compared with expiration (p = 0.02). It was also decreased in the 0.1-Hz-SlowIns compared with the 0.2-Hz condition (p = 0.01). Slow breathing also increased the amplitude of respiratory sinus arrhythmia (RSA), although these changes were not significantly associated with changes in pain responses.
A number of studies on humans and animals have demonstrated better auditory abilities in blind wi... more A number of studies on humans and animals have demonstrated better auditory abilities in blind with respect to sighted subjects and have tried to define the mechanisms through which this compensation occurs. The aim of the present study, therefore, was to examine the participation of primary visual cortex (V1) to auditory processing in early enucleated rats. Here we show, using gaussian noise bursts, that about a third of the cells in V1 responded to auditory stimulation in blind rats and most of these (78%) had ON-type responses and low spontaneous activity. Moreover, they were distributed throughout visual cortex without any apparent tonotopic organization. Optimal frequencies determined using pure tones were rather high but comparable to those found in auditory cortex of blind and sighted rats. On the other hand, sensory thresholds determined at these frequencies were higher and bandwidths were wider in V1 of the blind animals. Blind and sighted rats were also stimulated for 60 min with gaussian noise, their brains removed and processed for c-Fos immunohistochemistry. Results revealed that c-Fos positive cells were not only present in auditory cortex of both groups of rats but there was a 10-fold increase in labeled cells in V1 and a fivefold increase in secondary visual cortex (V2) of early enucleated rats in comparisons to sighted ones. Also, the pattern of distribution of these labeled cells across layers suggests that the recruitment of V1 could originate at least in part through inputs arising from the thalamus. The ensemble of results appears to indicate that cross-modal compensation leading to improved performance in the blind depends on cell recruitment in V1 but probably also plastic changes in lower-and higher-order visual structures and possibly in the auditory system.
The evaluation of spinal cord neuronal activity in humans with functional magnetic resonance imag... more The evaluation of spinal cord neuronal activity in humans with functional magnetic resonance imaging (fMRI) is technically challenging. Major difficulties arise from cardiac and respiratory movement artifacts that constitute significant sources of noise. In this paper we assessed the Correction of Structured noise using spatial Independent Component Analysis (CORSICA). FMRI data of the cervical spinal cord were acquired in 14 healthy subjects using gradient-echo EPI. Nociceptive electrical stimuli were applied to the thumb. Additional data with short TR (250 ms, to prevent aliasing) were acquired to generate a spatial map of physiological noise derived from Independent Component Analysis (ICA). Physiological noise was subsequently removed from the long-TR data after selecting independent components based on the generated noise map. Stimulus-evoked responses were analyzed using the general linear model, with and without CORSICA and with a regressor generated from the cerebrospinal fluid region. Results showed higher sensitivity to detect stimulus-related activation in the targeted dorsal segment of the cord after CORSICA. Furthermore, fewer voxels showed stimulus-related signal changes in the CSF and outside the spinal region, suggesting an increase in specificity. ICA can be used to effectively reduce physiological noise in spinal cord fMRI time series.
Magnetic resonance imaging (MRI) has recently been applied to study spinal cord function in human... more Magnetic resonance imaging (MRI) has recently been applied to study spinal cord function in humans. However, spinal functional MRI (f MRI) encounters major technical challenges with cardiac noise being considered a major source of noise. The present study relied on echoplanar imaging of the cervical cord at short TR (TR=250 ms; TE=40 ms; flip=45°), combined with plethysmographic recordings to characterize the spatiotemporal properties of cardiac-induced signal changes in spinal f MRI. Frequency-based analyses examining signal change at the cardiac frequency confirmed mean fluctuations of about 10% (relative to the mean signal) in the spinal cord and surrounding cerebrospinal fluid (CSF), with maximal responses reaching up to 66% in some voxels. A spatial independent component analysis (sICA) confirmed that cardiac noise is an important source of variance in spinal f MRI with several components showing a response coherent with the cardiac frequency spectrum. The time course of the main cardiac components approximated a sinusoidal function tightly coupled to the cardiac systole with at least one component showing a comparable temporal profile across runs and subjects. Spatially, both the frequency-domain analysis and the sICA demonstrated cardiac noise distributed irregularly along the full rostrocaudal extent of the segments scanned with peaks concentrated in the ventral part of the lateral slices in all scans and subjects, consistent with the major channels of CSF flow. These results confirm that cardiacinduced changes are a significant source of noise likely to affect the detection of spinal Blood Oxygen Level Dependent (BOLD) responses. Most importantly, the complex spatiotemporal structure of cardiac noise is unlikely to be accounted for adequately by ad hoc linear methods, especially in data acquired using long TR (i.e. aliasing the cardiac frequency). However, the reliable spatiotemporal distribution of cardiac noise across scanning runs and within subjects may provide a valid means to identify and extract cardiac noise based on sICA methods.
Your article is protected by copyright and all rights are held exclusively by The Physiological S... more Your article is protected by copyright and all rights are held exclusively by The Physiological Society of Japan and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Journal of Manipulative and Physiological Therapeutics, 2012
Purpose: The purpose of this study was to investigate the alteration of pain-induced neuromuscula... more Purpose: The purpose of this study was to investigate the alteration of pain-induced neuromuscular trunk responses by expectations in healthy volunteers. Methods: Twenty-three asymptomatic participants performed series of flexion-extension movements in 3 different experimental conditions: innocuous heat stimulation (control) and noxious heat stimulation associated with expectations of low or high pain intensity. These stimuli were administered by a contact thermode placed over the lumbar region (L4 and L5) to assess the modulation of neuromuscular responses and kinematics during the flexionextension task. Surface electromyography (EMG) of lumbar erector spinae at L2 and L3 and L4 and L5 as well as lumbopelvic kinematic variables were compared across conditions. Results: Noxious stimulation significantly altered EMG responses but only in full trunk flexion. Interestingly, this alteration was significant only for muscles where noxious stimulation was applied (L4 and L5) and not for the other segment (L2 and L3). Conversely, expectations significantly altered EMG activity at L2 and L3 but not at the segment where noxious stimulation was applied. Conclusion: These results confirm previous findings and indicate that experimental pain can alter neuromuscular responses during a trunk flexion-extension task. Furthermore, this study suggests that expectations can alter some of these alterations. Future studies should determine whether neuromuscular changes induced by expectations may contribute to the transition from acute to chronic low-back pain. (J Manipulative Physiol Ther 2012;35:636-644)
Studies of electromyographic (EMG) activity and lumbopelvic rhythm have led to a better understan... more Studies of electromyographic (EMG) activity and lumbopelvic rhythm have led to a better understanding of neuromuscular alterations in chronic low back pain (cLBP) patients. Whether these changes reflect adaptations to chronic pain or are induced by acute pain is still unclear. This work aimed to assess the effects of experimental LBP on lumbar erector spinae (LES) EMG activity and lumbopelvic kinematics during a trunk flexion-extension task in healthy volunteers and LBP patients. The contribution of disability to these effects was also examined. Twelve healthy participants and 14 cLBP patients performed flexionextension tasks in three conditions; control, innocuous heat and noxious heat, applied on the skin over L5 or T7. The results indicated that noxious heat at L5 evoked specific increases in LES activity during static full trunk flexion and extension, irrespective of participants' group. Kinematic data suggested that LBP patients adopted a different movement strategy than controls when noxious heat was applied at the L5 level. Besides, high disability was associated with less kinematic changes when approaching and leaving full flexion. These results indicate that experimental pain can induce neuromechanical alterations in cLBP patients and healthy volunteers, and that higher disability in patients is associated with decreased movement pattern changes.
Patients with chronic low back pain exhibit characteristics such as clinical pain, psychological ... more Patients with chronic low back pain exhibit characteristics such as clinical pain, psychological symptoms and neuromuscular adaptations. The purpose of this study was to determine the independent contribution of clinical pain, psychological factors and neuromuscular adaptations to disability in patients with chronic low back pain. Clinical pain intensity, pain catastrophizing, fear-avoidance beliefs, anxiety, neuromuscular adaptations to chronic pain and neuromuscular responses to experimental pain were assessed in 52 patients with chronic low back pain. Lumbar muscle electromyographic activity was assessed during a flexion-extension task (flexion relaxation phenomenon) to assess both chronic neuromuscular adaptations and neuromuscular responses to experimental pain during the task. Multiple regressions showed that independent predictors of disability included neuromuscular adaptations to chronic pain (b = 0.25, p = 0.006, sr 2 = 0.06), neuromuscular responses to experimental pain (b = À0.24, p = 0.011, sr 2 = 0.05), clinical pain intensity (b = 0.28, p = 0.002, sr 2 = 0.08) and psychological factors (b = 0.58, p < 0.001, sr 2 = 0.32). Together, these predictors accounted for 65% of variance in disability (R 2 = 0.65 p < 0.001). The current investigation revealed that neuromuscular adaptations are independent from clinical pain intensity and psychological factors, and contribute to inter-individual differences in patients' disability. This suggests that disability, in chronic low back pain patients, is determined by a combination of factors, including clinical pain, psychological factors and neuromuscular adaptations.
In animals, somatic stimulation of the limbs can evoke sympathetic reflexes of supraspinal origin... more In animals, somatic stimulation of the limbs can evoke sympathetic reflexes of supraspinal origin. In addition, spinal reflexes can be elicited by stimulation of somatic tissues of the trunk. However, limited evidence is available concerning the specific modulation of sympathetic reflexes by afferents from the thoracic spine. This has also been largely overlooked in healthy humans. The aim of the present study was to determine whether tonic noxious heat (NH) applied to the skin over T3-T5 could segmentally increase supraspinal sympathetic reflexes (skin conductance responses - SCRs) induced by phasic electrical stimulation of the sural nerve. In addition, the effect of spinal manipulation (SM) on SCR amplitude and SCR amplification by NH was investigated. During the control session, palmar and plantar SCR amplitude was stable, showing no significant modulation. During NH and SM, however, palmar SCR amplitude was respectively increased and decreased in comparison to baseline, leading...
Enrichment of the environment is an effective means of enhancing neuronal development and plastic... more Enrichment of the environment is an effective means of enhancing neuronal development and plasticity but its effect on the cross-modal compensation resulting from sensory deprivation has never been investigated. The present study used c-Fos immunohistochemistry and dextran-biotin neuronal tracing to examine the reorganization of sensory modalities in the brain of anophthalmic mutant mice (ZRDCT/An) raised in either enriched or standard environments. Auditory stimulation was found to elicit strong neuronal activation in thalamic and cortical structures that are normally visual. An important finding was that the latter auditory-evoked cortical activity was considerably enhanced in blind mice raised in the enriched environment. The axonal tracing study demonstrated auditory inputs from the inferior colliculus to the visual thalamus. This animal model will be useful for understanding neuronal mechanisms underlying some cross-modal sensory phenomena observed in blind or deaf humans.
This study examines the effect of normal aging on temporal summation (TS) of pain and the nocicep... more This study examines the effect of normal aging on temporal summation (TS) of pain and the nociceptive flexion reflex (RIII). Two groups of healthy volunteers, young and elderly, received transcutaneous electrical stimulation applied to the right sural nerve to assess pain and the nociceptive flexion reflex (RIII-reflex). Stimulus intensity was adjusted individually to 120% of RIII-reflex threshold, and shocks were delivered as a single stimulus or as a series of 5 stimuli to assess TS at 5 different frequencies (0.17, 0.33, 0.66, 1, and 2 Hz). This study shows that robust TS of pain and RIII-reflex is observable in individuals aged between 18 and 75 years and indicates that these effects are comparable between young and older individuals. These results contrast with some previous findings and imply that at least some pain regulatory processes, including TS, may not be affected by normal aging, although this may vary depending on the method.
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