The Experts below are selected from a list of 6378 Experts worldwide ranked by ideXlab platform

Leah R Bent - One of the best experts on this subject based on the ideXlab platform.

  • cutaneous afferent innervation of the human Foot Sole what can we learn from single unit recordings
    Journal of Neurophysiology, 2018
    Co-Authors: Nicholas D J Strzalkowski, Timothy J Inglis, Ryan M Peters, Leah R Bent
    Abstract:

    Cutaneous afferents convey exteroceptive information about the interaction of the body with the environment and proprioceptive information about body position and orientation. Four classes of low-t...

  • the firing characteristics of Foot Sole cutaneous mechanoreceptor afferents in response to vibration stimuli
    Journal of Neurophysiology, 2017
    Co-Authors: Nicholas D J Strzalkowski, Leah R Bent
    Abstract:

    Our work provides a mechanistic look at the capacity of Foot Sole cutaneous afferents to respond to vibration of varying frequency and amplitude. We found that Foot Sole afferent classes are unique...

  • Foot Sole skin vibration perceptual thresholds are elevated in a standing posture compared to sitting
    Gait & Posture, 2016
    Co-Authors: Robyn L Mildren, Nicholas D J Strzalkowski, Leah R Bent
    Abstract:

    Foot Sole sensitivity is commonly assessed while individuals are seated or prone; however the primary role of Foot Sole cutaneous feedback is for the control of upright stance and gait. The aim of this study was to compare vibration perceptual thresholds across the Foot Sole between sitting and standing postures. Vibration perceptual thresholds were measured in sitting and standing postures in 18 healthy participants (8 male) using a custom vibration device. Two Foot Sole locations (heels and metatarsals) were tested at four vibration frequencies (3, 15, 40, and 250Hz) selected to target different cutaneous afferent populations. At each frequency, perceptual thresholds across the Foot Sole were significantly higher in the standing posture compared to the sitting posture; this is indicative of lower sensitivity while standing. In addition, threshold differences between the heels and metatarsals for lower frequency vibratory stimuli were more pronounced while standing, with higher thresholds observed at the heels. Our results demonstrate that standing significantly alters sensitivity across the Foot Sole. Therefore, conducting perceptual tests at the Foot Sole during stance could potentially provide more direct information about the ability of cutaneous afferents to signal tactile information in a state where this feedback can contribute to postural control.

  • thresholds of cutaneous afferents related to perceptual threshold across the human Foot Sole
    Journal of Neurophysiology, 2015
    Co-Authors: Nicholas D J Strzalkowski, Robyn L Mildren, Leah R Bent
    Abstract:

    Perceptual thresholds are known to vary across the Foot Sole, despite a reported even distribution in cutaneous afferents. Skin mechanical properties have been proposed to account for these differences; however, a direct relationship between Foot Sole afferent firing, perceptual threshold, and skin mechanical properties has not been previously investigated. Using the technique of microneurography, we recorded the monofilament firing thresholds of cutaneous afferents and associated perceptual thresholds across the Foot Sole. In addition, receptive field hardness measurements were taken to investigate the influence of skin hardness on these threshold measures. Afferents were identified as fast adapting [FAI (n = 48) or FAII (n = 13)] or slowly adapting [SAI (n = 21) or SAII (n = 20)], and were grouped based on receptive field location (heel, arch, metatarsals, toes). Overall, perceptual thresholds were found to most closely align with firing thresholds of FA afferents. In contrast, SAI and SAII afferent firing thresholds were found to be significantly higher than perceptual thresholds and are not thought to mediate monofilament perceptual threshold across the Foot Sole. Perceptual thresholds and FAI afferent firing thresholds were significantly lower in the arch compared with other regions, and skin hardness was found to positively correlate with both FAI and FAII afferent firing and perceptual thresholds. These data support a perceptual influence of skin hardness, which is likely the result of elevated FA afferent firing threshold at harder Foot Sole sites. The close coupling between FA afferent firing and perceptual threshold across Foot Sole indicates that small changes in FA afferent firing can influence perceptual thresholds.

  • thresholds of skin sensitivity are partially influenced by mechanical properties of the skin on the Foot Sole
    Physiological Reports, 2015
    Co-Authors: Nicholas D J Strzalkowski, John J Triano, Chris K Lam, Cale A Templeton, Leah R Bent
    Abstract:

    Across the Foot Sole, there are vibration and monofilament sensory differences despite an alleged even distribution of cutaneous afferents. Mechanical property differences across Foot Sole sites have been proposed to account for these differences. Vibration (VPT; 3 Hz, 40 Hz, 250 Hz), and monofilament (MF) perception threshold measurements were compared with skin hardness, epidermal thickness, and stretch response across five Foot Sole locations in young healthy adults (n = 22). Perceptual thresholds were expected to correlate with all mechanical property measurements to help address sensitivity differences between sites. Following this hypothesis, the MedArch was consistently found to be the thinnest and softest site and demonstrated the greatest sensitivity. Conversely, the Heel was found to be the thickest and hardest site, and was relatively insensitive across perceptual tests. Site differences were not observed for epidermal stretch response measures. Despite an apparent trend of elevated sensory threshold at harder and thicker sites, significant correlations between sensitivity measures and skin mechanical properties were not observed. Skin hardness and epidermal thickness appeared to have a negligible influence on VPT and minor influence on MF within this young healthy population. When normalized (% greater or smaller than subject mean) to the subject mean for each variable, significant positive correlations were observed between MF and skin hardness (R 2 = 0.422, P < 0.0001) and epidermal thickness (R 2 = 0.433, P < 0.0001) providing evidence that skin mechanics can influence MF threshold. In young healthy adults, differences in sensitivity are present across the Foot Sole, but cannot Solely be accounted for by differences in the mechanical properties of the skin.

Maria Knikou - One of the best experts on this subject based on the ideXlab platform.

  • effects of mechanical vibration of the Foot Sole and ankle tendons on cutaneomuscular responses in man
    Neuroscience Letters, 2013
    Co-Authors: Andrew C Smith, Chaithanya K Mummidisetty, William Z Rymer, Maria Knikou
    Abstract:

    The modulation of cutaneomuscular responses in response to mechanical vibration applied to the Foot Sole and to the ankle tendons was established in ten healthy subjects. The effects of mechanical vibration applied to the skin adjacent to the tibialis anterior (TA) and Achilles tendons were examined in two subjects. With the subjects seated, mechanical vibration applied to the TA and/or Achilles tendons significantly depressed the cutaneomuscular responses in all subjects, regardless of the frequency (50, 150, 250 Hz) of vibration. Mechanical vibration applied either to the Foot Sole or to the skin adjacent to the tendons induced no significant effects. The demonstration that mechanical vibration applied to muscle tendons exerts an inhibitory effect on cutaneomuscular responses supports the hypothesis that receptors that mediate body kinesthesia can be used as a vehicle to alter the spinal excitability state. The data suggests that tendon vibration could be utilized in neurological disorders to induce exogenous-mediated potentiation of presynaptic inhibition.

  • The action of plantar pressure on flexion reflex pathways in the isolated human spinal cord.
    Clinical Neurophysiology, 2008
    Co-Authors: Bernard A. Conway, Maria Knikou
    Abstract:

    Abstract Objective To investigate the conditioning effects of plantar pressure on flexion reflex excitability in patients with motor complete spinal cord injury (SCI). Methods In five motor complete SCI subjects, the non-nociceptive flexion reflex was evoked via electrical stimulation of the right sural nerve and was recorded from the ipsilateral tibialis anterior muscle. Pressure ranging from 25 to 80 kPa was applied to the metatarsal heads through an adjustable platform incorporated into a Foot rest and a comparison of the reflex size made between control conditions and during pressure application. Results In all subjects, a significant depression of the long latency flexion reflex was observed when pressure was applied to the Foot Sole. The short latency flexion reflex appearing at latencies less than 100 ms was absent in all patients. Conclusions The results demonstrate that flexion reflex excitability in the isolated human spinal cord can be modulated by adequate activation of plantar mechanoreceptors. Significance Activation of plantar mechanoreceptors is a feature of normal standing and walking. Rehabilitation for standing and walking in SCI commonly uses body weight support based protocols. The strong inhibitory actions of plantar pressure on reflex pathways in the isolated human spinal cord suggest that sensory feedback from the Foot Sole may be an important factor in successful rehabilitation of standing and stepping in SCI patients.

  • Effects of changes in hip joint angle on H-reflex excitability in humans
    Experimental Brain Research, 2002
    Co-Authors: Maria Knikou, William Zev Rymer
    Abstract:

    We examined the amplitude modulation of the Soleus (Sol) H-reflex during controlled variations of the hip joint angle in 21 healthy adult human subjects. Hip angle variations were imposed separately, or in combination either with stimulation of the plantar skin or with electrical activation of muscle afferents from the medial gastrocnemius (MG) nerve. We found that with subjects in the supine position, flexion of the hip significantly depressed Sol H-reflex excitability, by as much as 50% of control reflex values (Ho) recorded at 10° of hip flexion. Conversely, significant facilitation of the H-reflex was observed when the hip joint was extended (10°), with amplitudes reaching 200±15.3% of Ho. Changes in H-reflex amplitude were also observed during electrical stimulation of either the Foot Sole or the MG nerve, when stimuli were delivered at different hip angles. Foot Sole stimulation resulted in facilitation of the H-reflex with the hip extended while depression of the reflex was recorded with the hip flexed. In contrast, MG nerve stimulation at group-I muscle afferent strength resulted in a significant increase in the Sol H-reflex magnitude with the hip flexed, while during hip extension, suppression of the H-reflex was present. This study provides evidence for the existence of a spinal mechanism, determined principally by the hip joint angle, which promotes switching between inhibitory and facilitatory pathways during hip flexion and extension. The origins of such a spinal mechanism are discussed.

  • modulation of Soleus h reflex following ipsilateral mechanical loading of the Sole of the Foot in normal and complete spinal cord injured humans
    Neuroscience Letters, 2001
    Co-Authors: Maria Knikou, B A Conway
    Abstract:

    The modulation of the Soleus H-reflex in response to tonic mechanical loading applied to the plantar aspect of the Foot Sole was examined in nine normal subjects and five patients with a clinically defined complete spinal cord injury (SCI). With the subjects seated, tonic pressure applied to the metatarsal region of the ipsilateral Foot Sole significantly depressed Soleus H-reflex excitability in all subjects. The demonstration of a decrease in H-reflex excitability in both subject groups as a result of applied pressure to the Foot suggests that the change in reflex excitability is the result of a common spinal mechanism. The results highlight the modulatory effects that natural stimulation of cutaneous afferents can have on reflex excitability and may have practical application in gait rehabilitation and in the management of disorders of muscle tone following SCI.

Brad Manor - One of the best experts on this subject based on the ideXlab platform.

  • an mri compatible Foot Sole stimulation system enabling characterization of the brain response to walking related tactile stimuli
    Frontiers in Neuroscience, 2019
    Co-Authors: Tingwei Zhang, Brad Manor, Kai Zhang, Yufeng Chai, Xiaoying Wang, Junhong Zhou, Yunfei Long, Jue Zhang, Jing Fang
    Abstract:

    Foot-Sole somatosensory impairment is a main contributor to balance decline and falls in aging and disease. The cortical networks involved in walking-related Foot Sole somatosensation, however, remain poorly understood. We thus created and tested a novel MRI-compatible device to enable study of the cortical response to pressure stimuli applied to the Foot Sole that mimic those stimuli experienced when walking. The device consists of a dual-drive stimulator equipped with two pneumatic cylinders, which are separately programed to apply pressure waveforms to the entire Foot Sole. In a sample of nine healthy younger adults, the pressure curve applied to the Foot Sole closely correlated with that experienced during over ground walking (r = 0.811 ± 0.043, P < 0.01). MRI compatibility testing indicated that the device has no or negligible impact on MR image quality. Gradient-recalled echo-planar images of nine healthy young adults using a block-designed 3.5-min walking-related stimulation revealed significant activation within the supplementary motor area, supramarginal gyrus, paracingulate gyri, insula, precentral gyrus, middle temporal gyrus, and hippocampus (uncorrected P < 0.001, k ≥ 10). Together, these results indicate that this stimulation system is MRI-compatible and capable of mimicking walking-related pressure waveforms on Foot Sole. It may thus be used as a research tool to identify cortical targets for interventions (e.g., non-invasive brain stimulation) aimed at enhancing this important source of input to the locomotor control system.

  • transcranial direct current stimulation enhances Foot Sole somatosensation when standing in older adults
    Experimental Brain Research, 2018
    Co-Authors: Junhong Zhou, Brad Manor, Lewis A Lipsitz, Jue Zhang, Jing Fang
    Abstract:

    Foot-Sole somatosensation is critical for safe mobility in older adults. Somatosensation arises when afferent input activates a neural network that includes the primary somatosensory cortex. Transcranial direct current stimulation (tDCS), as a strategy to increase somatosensory cortical excitability, may, therefore, enhance Foot-Sole somatosensation. We hypothesized that a single session of tDCS would improve Foot-Sole somatosensation, and thus mobility, in older adults. Twenty healthy older adults completed this randomized, double-blinded, cross-over study consisting of two visits separated by one week. On each visit, standing vibratory threshold (SVT) of each Foot and the timed-up-and-go test (TUG) of mobility were assessed immediately before and after a 20-min session of tDCS (2.0 mA) or sham stimulation with the anode placed over C3 (according to the 10/20 EEG placement system) and the cathode over the contralateral supraorbital margin. tDCS condition order was randomized. SVT was measured with a shoe inSole system. This system automatically ramped up, or down, the amplitude of applied vibrations and the participant stated when they could or could no longer feel the vibration, such that lower SVT reflected better somatosensation. The SVTs of both Foot Soles were lower following tDCS as compared to sham and both pre-test conditions [F(1,76) > 3.4, p < 0.03]. A trend towards better TUG performance following tDCS was also observed [F(1,76) = 2.4, p = 0.07]. Greater improvement in SVT (averaged across feet) moderately correlated with greater improvement in TUG performance (r = 0.48, p = 0.03). These results suggest that tDCS may enhance lower-extremity somatosensory function, and potentially mobility, in healthy older adults.

  • direct current stimulation over the human sensorimotor cortex modulates the brain s hemodynamic response to tactile stimulation
    European Journal of Neuroscience, 2015
    Co-Authors: Ye Wang, Xiaoying Wang, Junhong Zhou, Jue Zhang, Jing Fang, Peter J Fried, Alvaro Pascualleone, Brad Manor
    Abstract:

    Tactile stimuli produce afferent signals that activate specific regions of the cerebral cortex. Noninvasive transcranial direct current stimulation (tDCS) effectively modulates cortical excitability. We therefore hypothesised that a single session of tDCS targeting the sensory cortices would alter the cortical response to tactile stimuli. This hypothesis was tested with a block-design functional magnetic resonance imaging protocol designed to quantify the blood oxygen level-dependent response to controlled sinusoidal pressure stimulation applied to the right Foot Sole, as compared with rest, in 16 healthy young adults. Following sham tDCS, right Foot Sole stimulation was associated with activation bilaterally within the precentral cortex, postcentral cortex, middle and superior frontal gyri, temporal lobe (subgyral) and cingulate gyrus. Activation was also observed in the left insula, middle temporal lobe, superior parietal lobule, supramarginal gyrus and thalamus, as well as the right inferior parietal lobule and claustrum (false discovery rate corrected, P < 0.05). To explore the regional effects of tDCS, brain regions related to somatosensory processing, and cortical areas underneath each tDCS electrode, were chosen as regions of interest. Real tDCS, as compared with sham tDCS, increased the percent signal change associated with Foot stimulation relative to rest in the left posterior paracentral lobule. These results indicate that tDCS acutely modulated the cortical responsiveness to controlled Foot pressure stimuli in healthy adults. Further study is warranted, in both healthy individuals and patients with sensory impairments, to link tDCS-induced modulation of the cortical response to tactile stimuli with changes in somatosensory perception.

  • h index is important for postural control for people with impaired Foot Sole sensation
    PLOS ONE, 2015
    Co-Authors: Shuqi Zhang, Brad Manor
    Abstract:

    Introduction People with Peripheral Neuropathy (PN), especially those with impaired sensory inputs through the small-afferent fiber (type II afferent fibers) reflex loop (SAF), might depend more on the large-afferent fiber (type I afferent fibers) reflex loop (LAF) for postural control. Purpose To examine whether the function of the LAF reflex loop, reflected by the H-reflex and ankle joint proprioception, influences postural control when the SAF reflex loop is impaired, as indicated by reduced Foot Sole cutaneous sensation. Methods Thirteen participants (8 women, 5 men) diagnosed with PN and 12 age-matched controls (7 women, 5 men) completed the testing protocol. Measures of interest included the H-index, active (AAP) and passive (PAP) ankle proprioception, plantar pressure sensitivity (PPS), average sway velocity (VAVG) and area (A95) during 30 seconds eyes-closed standing, 6-minute walk distance (6MWD) and timed up-and-go duration (TUG). Results Statistically significant group-dependent regression was observed between VAVG and H-index. Compared to the control group, the PN group demonstrated reduced PPS (2.0 ± 1.9 vs. 4.2 ± 1.2, P < .05) and H-index (63.6 ± 10.9 vs. 76.4 ± 16.0, P < .05), greater VAVG (3.5 ± 2.1 vs. 1.6 ± 0.6cm/s, P < .05) and A95 (10.0 ± 10.1 vs. 2.5 ± 1.5cm2, P < .05), shorter 6MWD (442.2 ± 93.0 vs. 525.3 ± 68.2m, P < .05), and longer TUG (9.4 ± 1.6 vs. 6.5 ± 1.3s, P < .05). Within the PN group, but not the control group, the H-index was correlated with VAVG (r = -.56, P < .05). Moreover, within the PN group only, PAP scores were correlated with 6MWD (r = -.68, P < .05) and TUG (r = -.59, P < .05) performance. No other statistically significant group difference, correlation or group-dependent regression was observed. Conclusion VAVG, 6MWD, and TUG correlated with LAF reflex loop function observed among those with impaired functioning of the SAF reflex loop. This observation suggests that the LAF reflex loop may be critical to the control of balance in those individuals suffering from small-fiber PN.

  • novel mri compatible tactile stimulator for cortical mapping of Foot Sole pressure stimuli with fmri
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Ying Hao, Brad Manor, Jing Liu, Kai Zhang, Yufeng Chai, Lewis A Lipsitz, Chungkang Peng, Vera Novak, Xiaoying Wang
    Abstract:

    Foot Sole somatosensory feedback is critical to motor control and declines with aging and disease. To enable study of cortical networks underlying Foot Sole somatosensation we developed a pneumatic tactile stimulator capable of producing 1-DOF oscillations with preset waveform, frequency (≤10 Hz), force magnitude (5-500 N), duty cycle (20%-100%) and contacted surface area over which pressures are applied to the Foot Sole. Image tests (anatomical/functional/field map) of a phantom demonstrated that the device is compatible with 3T MRI. GRE-EPI images of seven healthy young adults using a typical block-designed 1Hz sinusoidal stimulation protocol revealed significant activation contralaterally within the primary somatosensory cortex and paracentral gyrus, and bilaterally within the secondary somatosensory cortex. The stimulation system may therefore serve as a research tool to study functional brain networks involved in the perception and modulation of Foot Sole somatosensation and its relationship to motor control.

Nicholas D J Strzalkowski - One of the best experts on this subject based on the ideXlab platform.

  • cutaneous afferent innervation of the human Foot Sole what can we learn from single unit recordings
    Journal of Neurophysiology, 2018
    Co-Authors: Nicholas D J Strzalkowski, Timothy J Inglis, Ryan M Peters, Leah R Bent
    Abstract:

    Cutaneous afferents convey exteroceptive information about the interaction of the body with the environment and proprioceptive information about body position and orientation. Four classes of low-t...

  • the firing characteristics of Foot Sole cutaneous mechanoreceptor afferents in response to vibration stimuli
    Journal of Neurophysiology, 2017
    Co-Authors: Nicholas D J Strzalkowski, Leah R Bent
    Abstract:

    Our work provides a mechanistic look at the capacity of Foot Sole cutaneous afferents to respond to vibration of varying frequency and amplitude. We found that Foot Sole afferent classes are unique...

  • Foot Sole skin vibration perceptual thresholds are elevated in a standing posture compared to sitting
    Gait & Posture, 2016
    Co-Authors: Robyn L Mildren, Nicholas D J Strzalkowski, Leah R Bent
    Abstract:

    Foot Sole sensitivity is commonly assessed while individuals are seated or prone; however the primary role of Foot Sole cutaneous feedback is for the control of upright stance and gait. The aim of this study was to compare vibration perceptual thresholds across the Foot Sole between sitting and standing postures. Vibration perceptual thresholds were measured in sitting and standing postures in 18 healthy participants (8 male) using a custom vibration device. Two Foot Sole locations (heels and metatarsals) were tested at four vibration frequencies (3, 15, 40, and 250Hz) selected to target different cutaneous afferent populations. At each frequency, perceptual thresholds across the Foot Sole were significantly higher in the standing posture compared to the sitting posture; this is indicative of lower sensitivity while standing. In addition, threshold differences between the heels and metatarsals for lower frequency vibratory stimuli were more pronounced while standing, with higher thresholds observed at the heels. Our results demonstrate that standing significantly alters sensitivity across the Foot Sole. Therefore, conducting perceptual tests at the Foot Sole during stance could potentially provide more direct information about the ability of cutaneous afferents to signal tactile information in a state where this feedback can contribute to postural control.

  • thresholds of cutaneous afferents related to perceptual threshold across the human Foot Sole
    Journal of Neurophysiology, 2015
    Co-Authors: Nicholas D J Strzalkowski, Robyn L Mildren, Leah R Bent
    Abstract:

    Perceptual thresholds are known to vary across the Foot Sole, despite a reported even distribution in cutaneous afferents. Skin mechanical properties have been proposed to account for these differences; however, a direct relationship between Foot Sole afferent firing, perceptual threshold, and skin mechanical properties has not been previously investigated. Using the technique of microneurography, we recorded the monofilament firing thresholds of cutaneous afferents and associated perceptual thresholds across the Foot Sole. In addition, receptive field hardness measurements were taken to investigate the influence of skin hardness on these threshold measures. Afferents were identified as fast adapting [FAI (n = 48) or FAII (n = 13)] or slowly adapting [SAI (n = 21) or SAII (n = 20)], and were grouped based on receptive field location (heel, arch, metatarsals, toes). Overall, perceptual thresholds were found to most closely align with firing thresholds of FA afferents. In contrast, SAI and SAII afferent firing thresholds were found to be significantly higher than perceptual thresholds and are not thought to mediate monofilament perceptual threshold across the Foot Sole. Perceptual thresholds and FAI afferent firing thresholds were significantly lower in the arch compared with other regions, and skin hardness was found to positively correlate with both FAI and FAII afferent firing and perceptual thresholds. These data support a perceptual influence of skin hardness, which is likely the result of elevated FA afferent firing threshold at harder Foot Sole sites. The close coupling between FA afferent firing and perceptual threshold across Foot Sole indicates that small changes in FA afferent firing can influence perceptual thresholds.

  • thresholds of skin sensitivity are partially influenced by mechanical properties of the skin on the Foot Sole
    Physiological Reports, 2015
    Co-Authors: Nicholas D J Strzalkowski, John J Triano, Chris K Lam, Cale A Templeton, Leah R Bent
    Abstract:

    Across the Foot Sole, there are vibration and monofilament sensory differences despite an alleged even distribution of cutaneous afferents. Mechanical property differences across Foot Sole sites have been proposed to account for these differences. Vibration (VPT; 3 Hz, 40 Hz, 250 Hz), and monofilament (MF) perception threshold measurements were compared with skin hardness, epidermal thickness, and stretch response across five Foot Sole locations in young healthy adults (n = 22). Perceptual thresholds were expected to correlate with all mechanical property measurements to help address sensitivity differences between sites. Following this hypothesis, the MedArch was consistently found to be the thinnest and softest site and demonstrated the greatest sensitivity. Conversely, the Heel was found to be the thickest and hardest site, and was relatively insensitive across perceptual tests. Site differences were not observed for epidermal stretch response measures. Despite an apparent trend of elevated sensory threshold at harder and thicker sites, significant correlations between sensitivity measures and skin mechanical properties were not observed. Skin hardness and epidermal thickness appeared to have a negligible influence on VPT and minor influence on MF within this young healthy population. When normalized (% greater or smaller than subject mean) to the subject mean for each variable, significant positive correlations were observed between MF and skin hardness (R 2 = 0.422, P < 0.0001) and epidermal thickness (R 2 = 0.433, P < 0.0001) providing evidence that skin mechanics can influence MF threshold. In young healthy adults, differences in sensitivity are present across the Foot Sole, but cannot Solely be accounted for by differences in the mechanical properties of the skin.

Ole Kæseler Andersen - One of the best experts on this subject based on the ideXlab platform.

  • central sensitization in spinal cord injured humans assessed by reflex receptive fields
    Clinical Neurophysiology, 2014
    Co-Authors: Jose Biurrun Manresa, Lars Arendtnielsen, Nanna B Finnerup, I L Johannesen, F Bieringsorensen, Troels S Jensen, Ole Kæseler Andersen
    Abstract:

    Abstract Objective To investigate the effects of central sensitization, elicited by intramuscular injection of capsaicin, by comparing the reflex receptive fields (RRF) of spinally-intact volunteers and spinal cord injured volunteers that present presensitized spinal nociceptive mechanisms. Methods Fifteen volunteers with complete spinal cord injury (SCI) and fourteen non-injured (NI) volunteers participated in the experiment. Repeated electrical stimulation was applied on eight sites on the Foot Sole to elicit the nociceptive withdrawal reflex (NWR). RRF were assessed before, 1 min after and 60 min after an intramuscular injection of capsaicin in the Foot Sole in order to induce central sensitization. Results Both groups presented RRF expansion and lowered NWR thresholds immediately after capsaicin injection, reflected by the enlargement of RRF sensitivity areas and RRF probability areas. Moreover, the topography of the RRF sensitivity and probability areas were significantly different in SCI volunteers compared to NI volunteers in terms of size and shape. Conclusions SCI volunteers can develop central sensitization, despite adaptive/maladaptive changes in synaptic plasticity and lack of supraspinal control. Significance Protective plastic mechanisms may still be functional in SCI volunteers.

  • Introducing the reflex probability maps in the quantification of nociceptive withdrawal reflex receptive fields in humans
    Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2010
    Co-Authors: Jose Biurrun Manresa, Michael Brun Jensen, Ole Kæseler Andersen
    Abstract:

    Abstract The aim of the present study was to improve the assessment of reflex receptive fields (RRF) in humans, using reflex sensitivity and reflex probability maps. Repeated electrical stimulation was applied to elicit the nociceptive withdrawal reflex (NWR) in fifteen healthy volunteers using two stimulation paradigms: fixed (FSI) and adjusted (ASI) stimulation intensities. Stimulation was applied on sixteen sites in the Foot Sole, and pain intensity ratings and EMG responses were recorded. RRF sensitivity and probability maps were derived, and RRF areas were calculated. During FSI, the stimulation intensities were constant and the pain ratings dropped significantly ( p p p

  • reflex receptive fields for human withdrawal reflexes elicited by non painful and painful electrical stimulation of the Foot Sole
    Clinical Neurophysiology, 2001
    Co-Authors: Ole Kæseler Andersen, Finn A. Sonnenborg, Lars Arendtnielsen
    Abstract:

    Abstract Objectives : Human withdrawal reflex receptive fields (RRFs) were assessed for 4 different electrical stimulus intensities, ranging from below the pain threshold (PTh) to up to two times the PTh intensity (0.8×, 1.2×, 1.6×, and 2.0×PTh). Methods : Thirteen subjects participated, and the reflexes were recorded in a sitting position. The stimuli were delivered in random order to 12 positions distributed over the Foot Sole. Tibialis anterior (TA), gastrocnemius medialis (GM), vastus lateralis (VL), and biceps femoris (BF) reflexes were recorded. Further, knee and ankle joint angle changes were recorded. Results : The strongest reflexes were seen in the TA compared with the other 3 muscles. Dorsi-flexion dominated distal to the talocrural joint corresponding to the TA receptive field area. An expansion of the RRF for the TA and GM was seen when increasing the stimulus intensity from 0.8×PTh to 1.2×PTh and from 1.2×PTh to 1.6×PTh, indicating a gradually increasing reflex threshold towards the border, where TA contraction is inappropriate in a withdrawal reaction. For the BF and VL, the borders of the RRF areas were not detected. By integrating the reflex size within the RRF (i.e. the reflex volume), gradually increasing reflexes for increasing stimulus intensity were seen in all 4 muscles tested, most clearly in the TA and GM. The subjective pain intensity correlated to the reflex volume for the TA, GM, and BF. Conclusions : In conclusion, the highest reflex sensitivity was seen in the centre of the RRF, while the stimulus intensity needed for eliciting a reflex increased towards the receptive field border. Within the RRF, stronger reflexes were evoked for increasing stimulus intensity. The limit in the size of the receptive field size for the TA and GM supports a modular withdrawal reflex organisation.

  • Modular organization of excitatory and inhibitory reflex receptive fields elicited by electrical stimulation of the Foot Sole in man.
    Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 2000
    Co-Authors: Finn A. Sonnenborg, Ole Kæseler Andersen, Lars Arendt-nielsen
    Abstract:

    Abstract Objectives : The present study aimed to investigate how the inhibitory and excitatory reflex components of the human (polysynaptic) withdrawal reflex are organized depending on the stimulation site. The reflexes were elicited during a voluntary pre-contraction (between 10 and 20% of maximum voluntary contraction) of two antagonistic muscles. Methods : Inhibitory and excitatory reflex receptive fields to tibialis anterior (TA) and Soleus (SO) were mapped in 14 healthy subjects using randomized electrical stimulation at 16 sites of the Foot Sole. Low, non-painful (3× perception threshold), and high, painful (1.5× pain threshold), stimulus intensities were used. Results : The inhibitory reflex receptive fields were organized in a highly functional manner supporting the action of the excitatory reflex. Together the two reflexes result in an optimal withdrawal from the stimulus. Low stimulation intensity was found sufficient to elicit the inhibitory reflex. High stimulation intensity caused a reversal of the inhibition to excitation in tibialis anterior. In Soleus the inhibition was facilitated for stronger intensities. Conclusion : In conclusion, findings in animals of a modular organization of inhibitory reflexes are reproduced in humans.

  • modular organization of human leg withdrawal reflexes elicited by electrical stimulation of the Foot Sole
    Muscle & Nerve, 1999
    Co-Authors: Ole Kæseler Andersen, Finn A. Sonnenborg, Lars Arendtnielsen
    Abstract:

    Human withdrawal reflex receptive fields were determined for leg muscles by randomized, electrical stimulation at 16 different positions on the Foot Sole. Tibialis anterior, gastrocnemius medialis, peroneus longus, Soleus, rectus femoris, and biceps femoris reflexes, and ankle joint angle changes were recorded from 14 subjects in sitting position. Tibialis anterior reflexes were evoked at the medial, distal Foot and correlated well with ankle dorsal flexion. Gastrocnemius medialis reflexes were evoked on the heel and correlated with plantar flexion. Stimulation on the distal, medial Sole resulted in inversion (correlated best with tibialis anterior activity), whereas stimulation of the distal, lateral Sole evoked eversion. Biceps femoris reflexes were evoked on the entire Sole followed by a small reflex in rectus femoris. A detailed withdrawal reflex organization, in which each lower leg muscle has its own receptive field, may explain the ankle joint responses. The thigh activity consisted primarily of flexor activation.