Cutaneous Inputs Research Articles

Effects of reduced plantar cutaneous afferent feedback on locomotor adjustments in dynamic stability during perturbed walking

This study examined the effects of reduced plantar cutaneous afferent feedback on predictive and feedback adaptive locomotor adjustments in dynamic stability during perturbed walking. Twenty-two matched participants divided between an experimental-group and a control-group performed a gait protocol, which included surface alterations to one covered exchangeable gangway-element (hard/soft). In the experimental-group, cutaneous sensation in both foot soles was reduced to the level of sensory peripheral neuropathy by means of intradermal injections of an anaesthetic solution, without affecting foot proprioception or muscles. The gait protocol consisted of baseline trials on a uniformly hard surface and an adaptation phase consisting of nineteen trials incorporating a soft gangway-element, interspersed with three trials using the hard surface-element (2nd, 8th and 19th). Dynamic stability was assessed by quantifying the margin of stability (MS), which was calculated as the difference between the base of support (BS) and the extrapolated centre of mass (CM). The horizontal velocity of the CM and its vertical projection in the anterior–posterior direction and the eigenfrequency of an inverted pendulum determine the extrapolated-CM. Both groups increased the BS at the recovery step in response to the first unexpected perturbation. These feedback corrections were used more extensively in the experimental-group, which led to a higher MS compared to the control-group, i.e. a more stable body-position. In the adaptation phase the MS returned to baseline similarly in both groups. In the trial on the hard surface directly after the first perturbation, both groups increased the MS at touchdown of the disturbed leg compared to baseline trials, indicating rapid predictive adjustments irrespective of plantar cutaneous input. Our findings demonstrate that the locomotor adaptational potential does not decrease due to the loss of plantar sensation.

Somatosensory response properties of excitatory and inhibitory neurons in rat motor cortex

In sensory cortical networks, peripheral inputs differentially activate excitatory and inhibitory neurons. Inhibitory neurons typically have larger responses and broader receptive field tuning compared with excitatory neurons. These differences are thought to underlie the powerful feedforward inhibition that occurs in response to sensory input. In the motor cortex, as in the somatosensory cortex, cutaneous and proprioceptive somatosensory inputs, generated before and during movement, strongly and dynamically modulate the activity of motor neurons involved in a movement and ultimately shape cortical command. Human studies suggest that somatosensory inputs modulate motor cortical activity in a center excitation, surround inhibition manner such that input from the activated muscle excites motor cortical neurons that project to it, whereas somatosensory input from nearby, nonactivated muscles inhibit these neurons. A key prediction of this hypothesis is that inhibitory and excitatory motor cortical neurons respond differently to somatosensory inputs. We tested this prediction with the use of multisite extracellular recordings in anesthetized rats. We found that fast-spiking (presumably inhibitory) neurons respond to tactile and proprioceptive inputs at shorter latencies and larger response magnitudes compared with regular-spiking (presumably excitatory) neurons. In contrast, we found no differences in the receptive field size of these neuronal populations. Strikingly, all fast-spiking neuron pairs analyzed with cross-correlation analysis displayed common excitation, which was significantly more prevalent than common excitation for regular-spiking neuron pairs. These findings suggest that somatosensory inputs preferentially evoke feedforward inhibition in the motor cortex. We suggest that this provides a mechanism for dynamic selection of motor cortical modules during voluntary movements.

Functional implications of tactile projection patterns to the lateral hemispheres of the cerebellum of the albino rat: the legacy of Wally Welker

In the late 1970s, Wally Welker and his colleagues published a series of papers describing the first high-resolution physiological maps of tactile mossy fiber projections to the granule cell layer of the rat. Over the subsequent decade, his laboratory continued to explore the implications of these results for cerebellar connectivity and function while also extending the basic mapping results to a number of additional mammalian species. In each case, the maps revealed several surprising features, including a dominance of tactile (cutaneous inputs), robust short latency responses from the sensory periphery, and a fractured patchy somatotopic organization of receptive fields. This paper summarizes the major results of these micromapping experiments and reconsiders their implications for cerebellar function in light of more recent experimental data. The paper also explores the relationship between these fundamental discoveries and Wally Welker's theory-neutral approach to experimental science.

Cremaster muscle motor unit action potentials

Objective Motor unit action potentials (MUAPs) of human striated cremaster muscle (CM) have not been analysed previously, so we examined the MUAPs of the CM, to learn more about the physiology of this unusual striated muscle that works mostly without voluntary control. Methods MUAPs of human CM were investigated in 31 normal subjects. MUAPs were elicited by either a voluntarily contraction effort or mostly by the reflex response to the tactile stimulation of the inner thigh. Concentric needle study of jitter was also performed in 10 normal subjects. Results The total number of MUAPs was 289. Approximately 40% of all MUAPs were classified as simple MUAPs (mean duration 4.7 ± 1.7 ms), and the remainder were polyphasic potentials (mean duration 10.1 ± 3.9 ms). In jitter study, only 29 potential pairs were obtained. There was an increase in jitter value and intermittent blocking. The mean jitter value was 81.9 ± 56.8 μs. The MUAPs longer than 20 ms sometimes grouped as a single long potential or as different subgroups with time intervals between them. Conclusion The EMG results were similar to those obtained from patients with chronic neurogenic disorders despite the fact that the CMs studied were clinically and functionally normal in our healthy male subjects. Significance These findings suggest that the CM is an “embryogenic” striated muscle with polyneural innervation both at the muscle fibre and/or at the spinal cord level in adult males. Thus the CM has a weak cortical control but mostly excited by the cutaneous inputs.

Overestimation of force during matching of externally generated forces

If a weight is applied to a finger and the subject asked to produce the same force, the subject generates a force larger than the weight. That is, subjects overestimate the force applied by an external target when matching it. Details of this force overestimation are not well understood. We show that subjects overestimate small target weights, but not larger ones. Furthermore we show for the first time that the force overestimation consists of two components. The first component is a constant. The second component depends on the precise magnitude of the weight and is only present when subjects hold the target weight against gravity. We suggest that the two components are generated in different phases of the force-matching task, are due to different processes, and must have an influence on all proprioceptive judgements of force.

A precision-of-information explanation of sensory dominance

Subjects identified letters or judged the sizes of squares presented visually and/or haptically. The stimuli were presented as spatiotemporal patterns (pre-recorded movement pathways) matched to avoid favouring either mode. Visual explorers were shown pathways as either a 1 cm line tracing out the shape (moving window condition) or as a line moving behind a stationary 1 cm window (stationary window condition). Haptic explorers| fingertips were guided along raised-line pathways (moving window condition) or felt the shapes, depicted in raised-line drawings, moving under their static fingertip (stationary window condition). Visual and haptic performance did not differ but the moving window conditions yielded lower latencies than stationary window conditions in both modes. When squares of different sizes were presented simultaneously to vision and kinesthesis, vision was dominant. The reverse was true when tactile (cutaneous) input was added to the kinesthetic information. These findings support the optimal integration hypothesis in that precision of information is critically related to dominance, and they challenge the concept of sensory capture as a modality-specific phenomenon.

Deqi sensations without cutaneous sensory input: results of an RCT

BackgroundDeqi is defined in relation to acupuncture needling as a sensory perception of varying character. In a recently published sham laser validation study, we found that subjects in the verum and the sham laser group experienced deqi sensations. Therefore, we aim to further analyze whether the perceptions reported in the two study arms were distinguishable and whether expectancy effects exhibited considerable impact on our results.MethodsA detailed re-analysis focusing on deqi sensations was performed from data collected in a previously published placebo-controlled, double-blind, clinical cross-over trial for a sham laser evaluation. Thirty-four healthy volunteers (28 ± 10.7 years; 16 women, 18 men) received two laser acupuncture treatments at three acupuncture points LI4 (hégu), LU7 (liéque), and LR3 (táichong); once by verum laser and once using a sham device containing an inactive laser in randomized order. Outcome measures were frequency, intensity (evaluated by visual analogue scale; VAS), and quality of the subjects' sensations perceived during treatments (assessed with the "acupuncture sensation scale").ResultsBoth, verum and the sham laser acupuncture result in similar deqi sensations with regard to frequency (p-value = 0.67), intensity (p-value = 0.71) and quality (p-values between 0.15 - 0.98). In both groups the most frequently used adjectives to describe these perceptions were "spreading", "radiating", "tingling", "tugging", "pulsing", "warm", "dull", and "electric". Sensations reported were consistent with the perception of deqi as previously defined in literature. Subjects' conviction regarding the effectiveness of laser acupuncture or the history of having received acupuncture treatments before did not correlate with the frequency or intensity of sensations reported.ConclusionsSince deqi sensations, described as sensory perceptions, were elicited without any cutaneous sensory input, we assume that they are a product of non-specific effects from the overall treatment procedure. Expectancy-effects due to previous acupuncture experience and belief in laser acupuncture do not seem to play a major role in elicitation of deqi sensations. Our results give hints that deqi might be a central phenomenon of awareness and consciousness, and that its relevance should be taken into account, even in clinical trials. However, further research is required to understand mechanisms underlying deqi.

Perception of deqi without cutaneous sensory input: Results of an RCT

Perception of deqi without cutaneous sensory input: Results of an RCT

P17-13 Short-latency intracortical inhibition is not reduced by cutaneous afferent input in ageing men

P17-13 Short-latency intracortical inhibition is not reduced by cutaneous afferent input in ageing men

Cervix Stimulation Evokes Predominantly Subthreshold Synaptic Responses in Mouse Thoracolumbar and Lumbosacral Superficial Dorsal Horn Neurons

Sensory input from the female reproductive tract (FRT) plays a pivotal role in coordinating reproductive reflexes. Additionally, a number of disorders, especially chronic pelvic pain, may be due to disturbances in sensory processing of signals from the FRT. Our aim was to record synaptic responses in neurons from lumbar and sacral spinal cord segments during mechanical stimulation of the cervix. We developed an in vivo preparation of the mouse spinal cord to record synaptic potentials from superficial dorsal horn (SDH) neurons under whole-cell patch clamp recording conditions. We analyzed the strength and distribution of excitatory postsynaptic potentials in SDH neurons evoked during mechanical stimulation of the cervix and cutaneous sites. Resting membrane potential and neuronal input resistance was similar in thoracolumbar (TL, T13-L3) and lumbosacral (LS, L6-S2) segments. We elicited activity in 6/21 TL neurons and 15/39 LS neurons using mechanical stimulation of the cervix with a blunt probe. The majority of these neurons responded to cervix stimulation with bursts of subthreshold excitatory postsynaptic potentials (4/6 and 12/15 TL and LS neurons, respectively). The remainder responded with sufficient magnitude to generate action potentials (2/6 and 3/15 TL and LS neurons). Cutaneous synaptic inputs were also elicited in 11/21 TL neurons following stimulation of the flank/leg, 19/39 LS neurons by stimulation of the tail, and three LS neurons by perineal stimulation. Some neurons received convergent synaptic inputs from the cervix and cutaneous sites (4/6 TL and 4/15 LS). These data demonstrate that spinal projections of cervix afferents are widely dispersed in the SDH and considerable convergence exists between neurons innervating the cervix and cutaneous structures. Our results indicate that much of the synaptic activity evoked in SDH neurons following cervix stimulation is subthreshold.

Visual and haptic influence on perception of stimulus size

In six experiments, subjects judged the sizes of squares that were presented visually and/or haptically, in unimodal or bimodal conditions. We were interested in which mode most affected size judgments in the bimodal condition when the squares presented to each mode actually differed in size. Three factors varied: whether haptic exploration was passive or active, whether the choice set from which the subjects selected their responses was visual or haptic, and whether cutaneous information was provided in addition to kinesthetic information. To match the task for each mode, visual presentations consisted of a cursor that moved along a square pathway to correspond to the haptic experience of successive segments revealed during exploration. We found that the visual influence on size judgments was greater than the influence of haptics when the haptic experience involved only kinesthesis, passive movement, and a visual choice set. However, when cutaneous input was added to kinesthetic information, size judgments were most influenced by the haptic mode. The results support hypotheses of sensory integration, rather than capture of one sense by the other.

Repetetive hindlimb movement using intermittent adaptive neuromuscular electrical stimulation in an incomplete spinal cord injury rodent model

The long-term objective of this work is to understand the mechanisms by which electrical stimulation based movement therapies may harness neural plasticity to accelerate and enhance sensorimotor recovery after incomplete spinal cord injury (iSCI). An adaptive neuromuscular electrical stimulation (aNMES) paradigm was implemented in adult Long Evans rats with thoracic contusion injury (T8 vertebral level, 155 ± 2 Kdyne). In lengthy sessions with lightly anesthetized animals, hip flexor and extensor muscles were stimulated using an aNMES control system in order to generate desired hip movements. The aNMES control system, which used a pattern generator/pattern shaper structure, adjusted pulse amplitude to modulate muscle force in order to control hip movement. An intermittent stimulation paradigm was used (5-cycles/set; 20-second rest between sets; 100 sets). In each cycle, hip rotation caused the foot plantar surface to contact a stationary brush for appropriately timed cutaneous input. Sessions were repeated over several days while the animals recovered from injury. Results indicated that aNMES automatically and reliably tracked the desired hip trajectory with low error and maintained range of motion with only gradual increase in stimulation during the long sessions. Intermittent aNMES thus accounted for the numerous factors that can influence the response to NMES: electrode stability, excitability of spinal neural circuitry, non-linear muscle recruitment, fatigue, spinal reflexes due to cutaneous input, and the endogenous recovery of the animals. This novel aNMES application in the iSCI rodent model can thus be used in chronic stimulation studies to investigate the mechanisms of neuroplasticity targeted by NMES-based repetitive movement therapy.

New method of measuring wrist joint position sense avoiding cutaneous and visual inputs.

BackgroundAspects of afferent inputs, generally termed proprioception, are being increasingly studied. Extraneous factors such as cutaneous inputs can dramatically interfere while trying to design studies in order to determine the participation of the different structures involved in proprioception in the wrist position sense. We tried to determine validity and repeatability of a new wrist joint position measurement device using methodology designed to minimize extraneous factors and isolate muscle and joint inputs.MethodsIn order to test the reliability of the system, eighty young-adult subjects without musculoskeletal or neurologic impairments affecting the right upper extremity were tested using a custom made motion tracking system. Testing consisted of two conditions: active reproduction of active placement and passive reproduction of passive placement. Subjects performed two repetitions of each target position (10, 20, and 30° of flexion and extension) presented in a random order. Test- retest reliability was then tested.ResultsThe average constant error in the passive condition was -0.7° ± 4.7° as compared to the active condition at 3.7° ± 5.1°. Average absolute error in the passive condition was 4.9° ± 2.9° compared to the active condition in which absolute error was 5.9° ± 3.5°.DiscussionTest-retest repeatability in both conditions was less than the 5° magnitude typical of clinical goniometry. Errors in the active condition (less than 2°) were slightly smaller than the passive condition, and the passive condition was also associated with poorer consistency between apparatus sensors and skin sensors.ConclusionsThe current system for measurement of wrist joint proprioception allows the researcher to decrease extraneous influences that may affect joint position sense awareness, and will help in future study aiming to determine precisely the role of the different structure involved in proprioception.

Changes in synaptic populations in the spinal dorsal horn following a dorsal rhizotomy in the monkey

Studies in monkeys have shown substantial neuronal reorganization and behavioral recovery during the months following a cervical dorsal root lesion (DRL; Darian-Smith [2004] J. Comp. Neurol. 470:134-150; Darian-Smith and Ciferri [2005] J. Comp. Neurol. 491:27-45, [2006] J. Comp. Neurol. 498:552-565). The goal of the present study was to identify ultrastructural synaptic changes post-DRL within the dorsal horn (DH). Two monkeys received a unilateral DRL, as described previously (Darian-Smith and Brown [2000] Nat. Neurosci. 3:476-481), which removed cutaneous and proprioceptive input from the thumb, index finger, and middle finger. Six weeks before terminating the experiment at 4 post-DRL months, hand representation was mapped electrophysiologically within the somatosensory cortex, and anterograde tracers were injected into reactivated cortex to label corticospinal terminals. Sections were collected through the spinal lesion zone. Corticospinal terminals and inhibitory profiles were visualized by using preembedding immunohistochemistry and postembedding gamma-aminobutyric acid (GABA) immunostaining, respectively. Synaptic elements were systematically counted through the superficial DH and included synaptic profiles with round vesicles (R), pleomorphic flattened vesicles (F; presumed inhibitory synapses), similar synapses immunolabeled for GABA (F-GABA), primary afferent synapses (C-type), synapses with dense-cored vesicles (D, mostly primary afferents), and presynaptic dendrites of interneurons (PSD). Synapse types were compared bilaterally via ANOVAs. As expected, we found a significant drop in C-type profiles on the lesioned side ( approximately 16% of contralateral), and R profiles did not differ bilaterally. More surprising was a significant increase in the number of F profiles ( approximately 170% of contralateral) and F-GABA profiles ( approximately 315% of contralateral) on the side of the lesion. Our results demonstrate a striking increase in the inhibitory circuitry within the deafferented DH.

Optimal interaction of respiratory and thermal regulation at rest and during exercise: Role of a serotonin-gated spinoparabrachial thermoafferent pathway

Recent evidence indicates that the lateral parabrachial nucleus (LPBN) in dorsolateral pons is pivotal in mediating the feedback control of inspiratory drive by central chemoreceptor input and feedforward control of body temperature by cutaneous thermoreceptor input. The latter is subject to descending serotonergic inhibition which gates the transmission of ascending thermoafferent information from spinal dorsal horn to the LPBN. Here, a model is proposed which suggests that the LPBN may be important in balancing respiratory and thermal homeostasis, two conflicting goals that are heightened by environmental heat/cold stress or exercise where the effects of respiratory thermolysis become prominent. This optimization model of respiratory-thermoregulatory interaction is supported by a host of recent studies which demonstrate that animals with serotonin (5-HT) dysfunction at the spinal dorsal horn--due to 5-HT antagonism, genetic 5-HT defects or spinal cord injury--all display similar respiratory abnormalities that are consistent with hyperactivity of the spinoparabrachial thermoafferent (and pain) pathway.

Contribution of Hindpaw Cutaneous Inputs to the Control of Lateral Stability During Walking in the Cat

To delineate the role of cutaneous feedback from the paws in the regulation of balance during walking, we compared the corrective responses of cats to lateral support surface translation before and after cutaneous denervation of the hindpaws. In addition, we compared characteristics of undisturbed walking before and after denervation. Electromyographic and kinematic data were collected from three cats trained to walk across a walkway, the central portion of which could be unexpectedly translated laterally in either direction. Following denervation, all of the cats changed their step width, lowered their pelvis, and spent more time with the hindlegs in double-support when walking across the walkway. When displaced by lateral support surface translations, the denervated cats made larger lateral steps and required more than a single step to regain balance. However, none of the cats fell following the denervation. The appearance and latency of the responses evoked in the hindleg muscles by the perturbations were unaffected by the denervation. However, the amplitude of these responses was affected by the loss of cutaneous inputs. Responses evoked at paw contact were significantly reduced in most muscles in the absence of cutaneous input, whereas responses evoked at end of stance revealed significant increases in gluteus medius activity with little influence on the activity of other muscles. Therefore the loss of cutaneous inputs leads to instability during gait. Although cutaneous feedback from the hindpaws is not essential for triggering corrective responses to support surface disturbances, it appears that cutaneous inputs are important for scaling the responses initiated by other cues.

Tactile acuity in the blind: A closer look reveals superiority over the sighted in some but not all cutaneous tasks

Previous studies have shown that blind subjects may outperform the sighted on certain tactile discrimination tasks. We recently showed that blind subjects outperformed the sighted in a haptic 2D-angle discrimination task. The purpose of this study was to compare the performance of the same blind ( n = 16) and sighted ( n = 17, G1) subjects in three tactile discrimination tasks dependent solely on cutaneous inputs from the fingertip of the index finger, D2. A second group of sighted subjects ( n = 30, G2) were also tested. Texture discrimination thresholds were 0.62 (G1)–0.80 mm (G2) for the sighted subjects, and 0.64 mm for the blind (standard, 2 mm spatial period). Grating orientation thresholds were 0.99 (G1)–1.12 mm (G2) for the sighted subjects, and 0.96 mm for the blind. Finally, vibrotactile frequency discrimination thresholds (100 Hz standard) were 19.5 (G2) and 20.0 Hz (G1) for the sighted, and 16.5 Hz for the blind subjects. There were no significant differences in performance between the blind and the sighted subjects for the grating orientation or vibrotactile frequency discrimination tasks. In contrast, blind subjects outperformed the sighted for the texture discrimination task (G2 only), possibly reflecting the fact that the raised dot surfaces were similar to the dots forming Braille characters (all were fluent Braille readers).

Vitamin D: criteria for safety and efficacy

The functional status indicator for vitamin D, for both safety and efficacy, is serum 25-hydroxyvitamin D concentration. Efficacy for several health endpoints requires levels of 80 nmol/L or higher. Toxicity occurs at levels of 500 nmol/L or higher. The input needed for efficacy, in addition to typical food and cutaneous inputs, will usually be 1000-2000 IU/day of supplemental cholecalciferol. Toxicity is associated only with excessive supplemental intake (usually well above 20,000 IU/day).

Speech motor learning in profoundly deaf adults.

Speech production, like other sensorimotor behaviors, relies on multiple sensory inputs — audition, proprioceptive inputs from muscle spindles, and cutaneous inputs from mechanoreceptors in the skin and soft tissues of the vocal tract. However, the capacity for intelligible speech by deaf speakers suggests that somatosensory input on its own may contribute to speech motor control and perhaps even to speech learning. We assessed speech motor learning in cochlear implant recipients who were tested with their implants turned off. A robotic device was used to alter somatosensory feedback by displacing the jaw during speech. We found that with training implant subjects progressively adapted to the mechanical perturbation. Moreover, the corrections we observed were for movement deviations that were exceedingly small, on the order of millimetres, indicating that speakers have precise somatosensory expectations. Speech motor learning is significantly dependent on somatosensory input.

The role of cutaneous afferents in controlling locomotion evoked by epidural stimulation of the spinal cord in decerebrate cats

The effects of the cutaneous input on the formation of the locomotor pattern in conditions of epidural stimulation of the spinal cord in decerebrate cats were studied. Locomotor activity was induced by rhythmic stimulation of the dorsal surface of spinal cord segments L4-L5 at a frequency of 3-5 Hz. Electromyograms (EMG) recorded from the antagonist muscles quadriceps, semitendinosus, tibialis anterior, and gastrocnemius lateralis were recorded, along with the kinematics of stepping movements during locomotion on a moving treadmill and reflex responses to single stimuli. Changes in the pattern of reactions observed before and after exclusion of cutaneous receptors (infiltration of lidocaine solution at the base of the paw or irrigation of the paw pads with chlorothane solution) were assessed. This treatment led to impairment of the locomotor cycle: the paw was placed with the rear surface downward and was dragged along in the swing phase, and the duration of the stance phase decreased. Exclusion of cutaneous afferents suppressed the polysynaptic activity of the extensor muscles and the distal flexor muscle of the ipsilateral hindlimb during locomotion evoked by epidural stimulation of the spinal cord. The effects of exclusion of cutaneous afferents on the monosynaptic component of the EMG response were insignificant.