Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Subliminal Stimulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1998

Task-dependent facilitation of motor evoked potentials during dynamic and steady muscle contractions.

Task-dependent differences in the facilitation of motor evoked potentials (MEPs) following cortex stimulation were studied in a proximal (deltoid) and a distal muscle (abductor digiti minimi; ADM) in 23 healthy subjects during both dynamic and steady contractions of the target muscle under isometric and under nonisometric conditions. In the deltoid, MEP amplitudes were significantly greater if stimulation was performed during dynamic contractions than during steady contractions, despite equal background electromyographic levels just prior to the stimulus. The same task-specific extra facilitation of deltoid MEP amplitudes was also found with magnetic stimulation of the brain stem instead of the cortex in 3 subjects. In the ADM, no such task-dependent extra facilitation of MEPs during dynamic contractions was found. It is concluded that in the deltoid, during dynamic contractions, a greater proportion of the spinal motoneurons is close to depolarization threshold (greater "subliminal fringe") whereas the number of firing motoneurons is similar to that during steady contraction. The lack of task-dependent extra facilitation of MEPs in the ADM is explained by the predominant recruitment principle for force gradation in small hand muscles, which is in contrast to the predominant frequency principle used in proximal muscles.

Adult↗
PubMed1999

Motor system excitability in patients with restless legs syndrome.

In 18 patients with idiopathic restless legs syndrome (RLS), intracortical inhibition by paired transcranial magnetic stimulation (TMS) was significantly reduced for both foot and hand muscles, suggesting that the entire motor cortex is disinhibited in RLS. Decreased intracortical facilitation in the foot muscle but not in the hand muscle may be due to subliminal activation of the symptomatic lower limbs. Motor excitability measurements of single TMS were not altered. These results support a subcortical origin of RLS.

Aged↗
PubMed1997

Characteristics of surround inhibition in cat area 17.

The effects of stimuli falling outside the 'classical receptive field' and their influence on the orientation selectivity of cells in the cat primary visual cortex are still matters of debate. Here we examine the variety of effects of such peripheral stimuli on responses to stimuli limited to the receptive field. We first determined the extent of the classical receptive field by increasing the diameter of a circular patch of drifting grating until the response saturated or reached a maximum, and by decreasing the diameter of a circular mask in the middle of an extended grating, centred on the receptive field, until the cell just began to respond. These two estimates always agreed closely. We then presented an optimum grating of medium-to-high contrast filling the classical receptive field while stimulating the surround with a drifting grating that had the same parameters as the central stimulus but was varied in orientation. For all but five neurons (of 37 tested), surround stimulation produced clear suppression over some range of orientations, while none showed explicit facilitation under these conditions. For 11 cells (34% of those showing suppression), the magnitude of suppression did not vary consistently with the orientation of the surround stimulus. In the majority of cells, suppression was weakest for a surround grating oriented orthogonal to the cell's optimum. Nine of these cells (28%) exhibited maximum inhibition at the optimum orientation for the receptive field itself, but for 12 cells (38%) there was apparent 'release' from inhibition for surround gratings at or near the cell's optimum orientation and direction, leaving inhibition either maximal at angles flanking the optimum (9 cells) or broadly distributed over the rest of the orientation range (3 cells). This implies the existence of a subliminal facilitatory mechanism, tightly tuned at or near the cell's optimum orientation, extending outside the classical receptive field. For just two cells of 13 tested the preferred orientation for a central grating was clearly shifted towards the orientation of a surrounding grating tilted away from the cell's optimum. The contrast gain for central stimulation at the optimal orientation was measured with and without a surround pattern. For nine of 25 cells tested, surround stimulation at the cell's optimum orientation facilitated the response to a central grating of low contrast (< or =0.1) but inhibited that to a higher-contrast central stimulus: the contrast-response gain is reduced but the threshold contrast is actually decreased by surround stimulation. Hence the receptive field is effectively larger for low-contrast than for high-contrast stimuli. Inhibition from the periphery is usually greatest at or around the cell's optimum, while suppression within the receptive field has been shown to be largely non-selective for orientation. Inhibition by orientations flanking the optimum could serve to sharpen orientation selectivity in the presence of contextual stimuli and to enhance orientational contrast; and it may play a part in orientation contrast illusions.

Animals↗
PubMed1991

Reinforcement of motor evoked potentials in patients with spinal cord injury.

Transcranial magnetic stimulation of the motor cortex has been used to investigate the putative existence of spared motor pathways in spinal cord injured patients with clinically complete paralysis. Particular consideration was given to methods of neurological reinforcement likely to minimize the risk of false negative interpretation of absent motor evoked potentials (MEPs). The principal methods of reinforcement included target and remote muscle contractions and conditioning of MEPs with a brief (20 msec) train of cutaneous stimulation (500 Hz: duration 0.1 msec) delivered 20-150 msec prior to cortical stimulation. Twelve control subjects and 26 patients with severe traumatic spinal cord injury underwent cortical stimulation delivered from a Cadwell MES-10 (70-100% intensity) through a 9-cm focal-point coil. Electromyographic responses were recorded from surface electrodes in bipolar configuration and amplified (3 dB down at 10 Hz-1 kHz) prior to storage. MEPs were recorded, following reinforcement, in muscles with clinically complete paralysis in 4/26 patients. In each case, MEPs were of low amplitude (less than 0.5 mV), polyphasic, and with variable and prolonged latencies. MEPs were evoked in severely paretic (clinically incomplete paralysis) muscles in 6/8 patients only when neurological reinforcement was employed. Conditioning of MEPs in tibialis anterior with preceding cutaneous stimulation to the plantar surface (subthreshold for evoking a flexion reflex) yielded a well-defined modulation of MEP amplitude in control subjects. An early (Conditioning-Test (C-T) intervals 20-45 msec) period of inhibition of MEPs (mean = 60% of control) was followed by a period (C-T intervals 50-90 msec) of facilitation (mean = 345%) and a subsequent (C-T intervals 90-150 msec) period of inhibition (mean = 0%). In spinal cord injured patients the same conditioning paradigm failed to reveal MEPs, but did result in the appearance of suprathreshold flexion reflexes in 2 patients at 20-55 msec C-T intervals. This summation of convergent but subliminal cortical and cutaneous inputs to the target motoneuron pool provided additional evidence of preserved cortical influence on segmental structures that was not detectable by other means. These results extend previous reports of electrophysiological evidence of spared motor pathways in spinal cord injured patients with complete paralysis, and affirm the need for neurological reinforcement as a routine procedure in cortical stimulation studies of spinal cord injuries.

Adult↗
PubMed1988

The H reflex recovery curve reinvestigated: low-intensity conditioning stimulation and nerve compression disclose differential effects of presumed group Ia fibres in man.

The recovery curve of the soleus H reflex, evoked by stimulation of the tibial nerve in the popliteal fossa, was studied by applying an electrical conditioning stimulus to the inferior soleus nerve. Under these conditions a long-latency facilitatory phase could be superimposed on a long-lasting inhibition, the excitability cycle being therefore similar to that obtained by means of a paired shock to the tibial nerve. In order to identify the afferent fibres responsible for the effects observed, various conditioning stimulus strengths and nerve compression were used. A low-intensity stimulus induced only a facilitatory phase, while the inhibition promptly ensued on increasing stimulus strength, which remained however subliminal for activation of group II fibres. During calf compression exerted by a sphygmomanometer cuff placed between the conditioning and test stimuli, the facilitatory effects disappeared within 10 to 15 min, and the inhibitory ones disappeared within 25 to 30 min from the onset of compression. Tonic voluntary contraction enhanced both the inhibition and the facilitation. In a subject with complete spinal section, both inhibitory and facilitatory phases could be demonstrated on low-intensity stimulation. The present data, and previous results of ours, allow the following conclusions. (1) Facilitation and inhibition are produced by fibres likely belonging to group Ia spindle afferents. (2) Both effects are of spinal origin. (3) The spinal circuits mediating the effects may be modulated by descending commands. (4) The facilitation is sustained by tonic supraspinal influences while the inhibition is independent of it. Arguments are proposed against the hypotheses that the inhibition be due to transmitter depletion or to presynaptic mechanisms.

Adult↗
PubMed1988

Effects of ganglion blocking agents on post-train facilitation in the rabbit superior cervical ganglion.

The effect of ganglion blocking agents, hexamethonium and tubocurarine, on post-train facilitation and ganglionic transmission was studied and compared in isolated superior cervical ganglion of the rabbit, using electrophysiological technique--the conditioning-testing methodology. The preganglionic nerve trunk was stimulated, with either a single unconditioned stimulus (UR)-or a train of conditioning stimuli at 10 or 30 Hz, followed by a post-train test stimulus (PTR). The transmitted postganglionic, compound action potential (PCAP) was recorded following single and trains of stimuli, in the presence and absence of ganglion blocking drugs, hexamethonium (1-100 microM) and tubocurarine (1-100 microM). Hexamethonium and tubocurarine produced concentration-dependent reduction in the amplitude of the transmitted PCAP, increased post-train facilitation values and proportionately reduced those of the subliminal fringe (SF). The mean IC50 values (concentration to produce 50% block of PCAP) of hexamethonium and tubocurarine-induced blockade of the single unconditioned response were 15 +/- 1 microM and 26 +/- 2 microM (n = 6, P less than 0.01) respectively. A dose-ratio (tubocurarine)/hexamethonium) of 1.7 was obtained.

Action Potentials↗
PubMed2003

Proton-induced calcitonin gene-related peptide release from rat sciatic nerve axons, in vitro, involving TRPV1.

We have shown previously that rat sciatic nerve axons in vitro express sensitivity to capsaicin and heat and responded to these stimuli with a Ca2+-dependent and graded immunoreactive calcitonin gene-related peptide release. Morphological evidence for stimulated vesicular exocytosis and for the vanilloid receptor TRPV1 in the axolemma of the unmyelinated nerve fibres has also been presented. Here we used solutions of low pH, high K+ or 47 degrees C to stimulate isolated desheathed sciatic nerves measuring immunoreactive calcitonin gene-related peptide release. pH 6.1 increased immunoreactive calcitonin gene-related peptide release by 31% over baseline and pH 5.2 and 4.3 caused a log-linear concentration-dependent increase of 137 and 265%, respectively. The effect of pH 3.4 was out of the linear range and not reversible. Stimulation in Ca2+-free solutions and under increased intracellular Ca2+ buffering capacity strongly reduced the proton responses. The TRPV1 antagonists capsazepine and ruthenium red substantially reduced the effects of pH 5.2 but not pH 6.1. Combining a stimulus of 60 mm K+ with the subliminal pH 6.3 reduced the axonal immunoreactive calcitonin gene-related peptide response by 88%. The noxious heat response at pH 6.3, however, was only reduced by 39%, suggesting a hidden sensitization to heat by low pH. This was supported by an effect of capsazepine to reduce the combined response to half, indicative of an involvement of TRPV1 in the sensitization but not in the axonal heat response itself that was found to be resistant to capsazepine. Axonal calcitonin gene-related peptide release is thought to play a physiological role in activity-dependent autoregulation of endoneurial blood flow. Axonal sensitivity to and sensitization by protons may be a pathophysiological mechanism involved in certain peripheral neuropathies.

Animals↗
PubMed1985

Modulation of slow response excitability by calcium in rabbit atrial trabeculae.

Slow responses were induced in rabbit isolated left atrial trabeculae in a modified Tyrode solution containing 15 mM-KCl and 1 mM-BaCl2. Conventional electrophysiological techniques were employed for stimulating and recording membrane potentials. Under these conditions, the excitability of the slow response depends on the past excitatory history of the preparation. As the stimulation frequency increases (range: 0.08-1 Hz) for a conditioning period of stimulation, the excitability of the slow response increases. This can be demonstrated by a decrease in stimulus requirement necessary to maintain slow response excitation following the conditioning period of stimulation. It is shown that when extracellular Ca2+ concentration is reduced to 0.5 mM, that phenomenon of frequency-dependent slow response excitability disappears but slow responses can still be elicited. Also, the addition of D-600 to 2.7 mM-Ca2+ solutions depresses both the slow response and its frequency-dependent excitability. The absence of frequency-dependent slow response excitability is not related to the depression of the slow response upstroke caused by low-Ca2+ solutions. Increasing intracellular Ca2+ concentration by exposing the preparation to low-Na+ solutions or to ouabain did not revert the observed effects in low-Ca2+ solutions. The addition of substances (5 mM-caffeine or 0.35 microM-adrenaline) that potentiate the influx of Ca2+ in low-Ca2+ solutions was found to be effective in restoring the dependence of slow response excitability on the frequency of stimulation. The increase in extracellular Ca2+ above 4 mM depressed the excitation of the slow response. Above 5.4 mM-Ca2+, the excitation of the slow response was completely inhibited while the preparation displayed continuous oscillations in transmembrane potential. The presence of a subthreshold response (subliminal response) that precedes and triggers slow response excitation is accompanied by tension development. Since the subliminal response is responsible for the changes in slow response excitability it is proposed that the Ca2+ inflow during slow response electrogenesis modulates the excitability of the slow response. Two possible physiological implications for this finding are discussed.

Action Potentials↗
PubMed1990

Further studies on growth factor production by the TC-1 stromal cell line: pre-B stimulating activity.

Adherent murine stromal cells support long-term in vitro lymphopoiesis or myelopoiesis dependent on the culture conditions used. A cell line, TC-1, isolated from long-term liquid murine marrow cultures under conditions approaching those permissive for lymphoid growth, has been found to produce an activity that acts synergistically with interleukin-3 (IL-3) or colony-stimulating factor-1 (CSF-1) to stimulate in vitro myeloid colonies, but which has no intrinsic colony-stimulating activity. We report here the presence of multiple growth factors in conditioned medium (CM) from the TC-1 line, including granulocyte-macrophage colony-stimulating factor (GM-CSF) (bioassay with antibody blocking and messenger RNA [mRNA] analysis), granulocyte CSF (G-CSF) and IL-4 (factor-dependent cell line bioassay), and CSF-1 (radioimmunoassay, mRNA) along with a pre-B cell inducing activity, which appears separate from these CSFs and segregates with the myeloid synergizing activity through anion exchange, sizing, and Conconavalin A chromatography. Because these activities are not yet purified to homogeneity, their identity or lack of identity remains an open question. Assays of TC-1 CM or cellular mRNA analysis have given negative results for IL-1, IL-2, IL-3, IL-6, and IL-7, and IL-6 does not stimulate pre-B cells in this assay. However, IL-4 and G-CSF do stimulate in vitro induction of pre-B cells from pre-B and B-cell-depleted Balb/C marrow and are present in CM by selective cell line assay. A monoclonal antibody to IL-4 that inhibited its pre-B inducing activity did not inhibit pre-B inducing activity of TC-1 CM. These data suggest the existence of a unique synergizing and pre-B inducing factor(s) in TC-1 CM. Given the known capacity of subliminal levels of growth factors to act synergistically, an alternate possibility is that these biologic phenomena represent the actions of low concentrations of growth factors acting synergistically and possibly associated with some core protein.

Animals↗
PubMed2004

Training with computer-supported motor imagery in post-stroke rehabilitation.

Converging lines of evidence suggest that motor imagery (the mental simulation of a motor act within working memory) is associated with subliminal activation of the motor system. This observation has led to the hypothesis that cortical activation during motor imagery may affect the acquisition of specific motor skills and help the recovery of motor function. In this paper, we describe a clinical protocol in which we use interactive tools to stimulate motor imagery in hemiplegic stroke patients, thereby helping them to recover lost motor function. The protocol consists of an inpatient and an outpatient phase, combining physical and mental practice. In the inpatient phase, patients are trained in a laboratory setting, using a custom-made interactive workbench (VR Mirror). After discharge, patients use a portable device to guide mental and physical practice in a home setting. The proposed strategy is based on the hypotheses that: (a) combined physical and mental practice can make a cost-effective contribution to the rehabilitation of stroke patients, (b) effective mental practice is not possible without some form of support, from a therapist (as in our inpatient phase) or from technology (as in the outpatient phase), (c) the inclusion of an outpatient phase will allow the patient to practice more often than would otherwise be possible, therefore increasing the speed and/or effectiveness of learning, and (d) the use of interactive technology will reduce the patient's need for skilled support, therefore improving the cost-effectiveness of training.

Cerebral Infarction↗
PubMed2003

Differences in recruitment properties of the corticospinal pathway between lengthening and shortening contractions in human soleus muscle.

The purpose of this study was to investigate how the recruitment properties of the corticospinal pathway are modulated in the soleus muscle of the lower limb during lengthening (LEN) and shortening (SHO) contractions by comparing the shape of the input-output (I/O) relation of the corticospinal pathway. To this end, we investigated the relationship between various stimulus intensities applied via transcranial magnetic stimulation and the size of motor-evoked potentials in 14 healthy subjects during voluntary plantarflexion and dorsiflexion (active lengthening) with a similar background activity (BGA) level. The shape of this relationship was sigmoidal and was characterized by a plateau value, maximum slope and threshold. The plateau value was clearly lower during LEN contractions than during SHO contractions. Likewise, the maximum slope was lower during LEN contractions. However, the threshold did not differ significantly between the two tasks. Since the plateau value and the maximum slope clearly differed between LEN and SHO contractions despite the similarity of their BGA levels, the central nervous system appears to have a different activation strategy for each of these tasks. Namely, the relative balance between excitatory and inhibitory components of the corticospinal volleys, as well as the subliminal fringe of the corticospinal pathway, were reduced during LEN contractions compared with SHO contractions. These strategies may help to avoid reflexive contractions brought about by higher discharge of muscle spindles and enable fine motor actions in voluntary lengthening contractions.

Adult↗
PubMed1972

Facilitation and inhibition of cell groups within the superior cervical ganglion of the rabbit.

1. The patterns of facilitation and inhibition of the S(a) and S(b) components of the post-ganglionic compound action potential after a single conditioning stimulus were different and dependent on stimulus parameters.2. With submaximal conditioning and test stimuli, the S(a) component showed a phase of early facilitation (40-75 msec after the conditioning stimulus) followed by a prolonged tail of facilitation. With maximal stimuli, early facilitation and late facilitation (700-2000 msec after the conditioning stimulus) were separated by a phase of inhibition or relative inhibition, most pronounced 100-300 msec after the conditioning stimulus.3. During early facilitation, a submaximal S(a) response was facilitated by 33.1 +/- 3.9%, while a maximal S(a) response was facilitated by 14.5 +/- 2.9%.4. Providing preganglionic C fibres were excited, facilitation of the S(b) component remained relatively constant for 40-500 msec after the conditioning stimulus, with no phase of inhibition.5. Early facilitation of submaximal S(a) responses was greatest when the conditioning stimulus excited about 50% of the preganglionic B fibres, but that of maximal responses was greatest when the conditioning stimulus excited all the B fibres. The preganglionic C fibres modulated facilitation of the S(a) component. Maximal facilitation of this component was associated with depression of the S(b) component.6. Submaximal S(a) responses are more strongly inhibited than maximal S(a) responses 200 msec after a conditioning stimulus. The C fibre pathway seems able to modulate the degree of inhibition of the S(a) ganglion cells.7. A neuronal model with divergent and convergent preganglionic B and C fibres supplying S(a) ganglion cells is consistent with the results. The preganglionic input is able to vary the size of the subliminal fringe. The S(b) component is in part due to the S(a) ganglion cells firing to their C fibre input.

Action Potentials↗
PubMed1990

[Electric stimulation of the dental pulp in the evaluation of the central effect of analgesics].

We conducted a double-blind cross-over study in ten volunteers aged from 19 to 30 years, to compare the pain control effects of a single oral dose of two analgesic compounds (drug A: propyphenazone mg 250, ethylmorphine mg 5, caffeine mg 5; drug B: dipyrone mg 500, diphenhydramine mg 12.5, adiphenine mg 5, ethyl aminobenzoate mg 2.5) in an experimental pain model using stimulation of dental pulp. Constant voltage stimuli were delivered through silver chloride electrodes placed in contact with the vestibular surface of the upper medial incisor. At the beginning of the session, the pain input was graded by asking the subject to identify the weakest stimulus perceived (threshold level) and the strongest stimulus endurable (tolerance level). The range between threshold and tolerance level was divided in nine steps plus a subliminal step. The ten steps were delivered randomly, and each series of steps was repeated eight times. The subjects were instructed to rate the pain sensation in an arbitrary scale of 5 degrees. The procedure was repeated at 60 min and 180 min after drug administration. Each subject received two tablets of drug A or drug B in two different sessions at weekly intervals. Statistical analysis of the procedures showed that neither drug A nor drug B significantly affected the pain threshold. Drug A significantly reduced the total pain score (P less than 0.01) and its action peaked 60 min after administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2002

Priming of motion direction and area V5/MT: a test of perceptual memory.

Presentation of supraliminal or subliminal visual stimuli that can (or cannot) be detected or identified can improve the probability of the same stimulus being detected over a subsequent period of seconds, hours or longer. The locus and nature of this perceptual priming effect was examined, using suprathreshold stimuli, in subjects who received repetitive pulse transcranial magnetic stimulation over the posterior occipital cortex, the extrastriate motion area V5/MT or the right posterior parietal cortex during the intertrial interval of a visual motion direction discrimination task. Perceptual priming observed in a control condition was abolished when area V5/MT was stimulated but was not affected by magnetic stimulation over striate or parietal sites. The effect of transcranial magnetic stimulation (TMS) on priming was specific to site (V5/MT) and to task - colour priming was unaffected by TMS over V5/MT. The results parallel, in the motion domain, recent demonstrations of the importance of macaque areas V4 and TEO for priming in the colour and form domains.

Adult↗
PubMed2003

The effects of pictures of emotional faces on tonic and phasic autonomic cardiac control in women and men.

The aim of the present study was to examine autonomic function in response to negatively and positively valenced pictures under different levels of conscious recognition. Heart period variability (HPV) and heart rate (HR) reactivity were studied in 53 males and females who were being shown pictures of angry and happy faces. The pictures, which were backwardly masked, were presented once every 30 s during a 5-min period and under three conditions (counterbalanced for type of facial expression): below the level of conscious recognition (17 ms), at an intermediate level (56 ms), and at a clearly recognizable level (2370 ms). Analyses of HR power spectrum (for 5 min in each condition) in the high frequency region (HF: 0.15-0.5 Hz) that reflects respiratory sinus arrhythmia, as well as analysis of phasic heart rate responses (7.5 s in 0.5 epochs following every picture presentation) were carried out. The main findings were that HF-power was higher, and cardiac midinterval acceleration lower, in response to angry as opposed to happy faces, a result obtained only for the men, however. No interaction effect between facial expression and the three exposure conditions was found, suggesting that the pictures induced emotional activation both subliminally and supraliminally. The results were discussed in terms of increased attention to aversive stimuli.

Adult↗
PubMed1991

[Facilitation and recovery of the H-reflex in children].

Facilitation and recovery of the H-reflex were studied in 63 children with cerebral palsy, and the results were compared with those obtained for 60 normal children. H waves were recorded from the gastrocnemius with surface electrodes, after applying paired stimulations to the tibial nerve in the midpopliteal crease. In normal children, both the facilitation and the recovery showed a tendency to decrease with their development, while those for children with cerebral palsy were more marked than normal children in all age groups. The present study indicated that the excitability of spinal alpha motoneurons and the subliminal fringe in the motoneuron pool might change due to the maturation of and the damage to the central nervous system in children. We consider that H-reflex examination provides useful information for the supraspinal control to the spinal mechanism to regulate muscle contraction in children as well as in adults.

Adolescent↗
PubMed1990

Superposition of H reflexes on steady contractions in man.

1. The aim of the investigation was to study the influence of steady isometric contractions on H reflexes of human soleus muscle. 2. Stimulating and recording conditions were hardly affected by plantar flexions which subjects maintained in a force matching task. 3. If the interval between a preceding control and the test stimulus was less than 8 s the test H reflex was depressed in the relaxed subject. The depression was diminished or removed if the test reflex was superimposed on a background activity. The interval between control and test H reflex was at least 8 s in the following experiments. 4. H reflexes were nearly independent of steady plantar flexions on which they were superimposed. In some subjects, there was a slight increase with increasing torque. During dorsal flexions, H reflexes in all subjects were inhibited with increasing torque. 5. The relationship between test H reflexes, control H reflexes and background activity was evaluated by varying pseudo-randomly stimulus intensity and steady flexion torque. The surface defined by this three-dimensional relation approximated a plane suggesting linear properties of the H reflex. In some subjects threshold intensity decreased slightly with torque, in others it was constant. 6. In response to a warning signal, human subjects initiated steady plantar or dorsal flexions in both feet and, at the same time, they started to concentrate on a light at the onset of which they performed a unilateral ballistic plantar contraction as fast as possible. The relations between H reflex and maintained flexion force during the warning period of the reaction time task were identical to those during force matching, showing that the behavioural context did not modulate the relations. 7. The relations were also the same if reflexes were evoked bi- or unilaterally, illustrating the absence of a mutual modification of simultaneously evoked H reflexes. 8. The relation was the same with ipsilateral matching and relaxed contralateral muscles as with bilateral matching. If the ipsilateral side stayed flaccid contralateral matching increased H reflexes by about 20% above control values. 9. It was concluded that various factors can combine to produce an increase of H reflexes with torque, the most important of them being the use of short intervals between H reflexes. We have various evidence from the present experiments for believing that, in the relaxed subjects, the subliminal fringe was small and that although stimulus intensities below threshold could evoke an afferent volley, the effect of this on low-threshold motor units was prevented by presynaptic inhibition at the Ia terminals.

Biomechanical Phenomena↗
PubMed1996

A comparison of the effects of noxious and innocuous counterstimuli on experimentally induced itch and pain.

We have studied experimentally induced itch (using histamine iontophoresis) and pain (using topical mustard oil) in healthy human volunteers, measured using visual analogue scale (VAS) ratings. The effects of the following counterstimuli were evaluated: innocuous vibration; innocuous transcutaneous electrical nerve stimulation (TENS); innocuous warming of skin; noxious heating of skin; noxious chemical skin stimulation (using mustard oil); mildly noxious constant current transdermal electrical stimulation. Innocuous stimuli applied 2 min after histamine or mustard oil challenge produced a modest reduction of itch and pain ratings (20-30%), which did not persist for more than 20 sec when the counterstimuli were removed. These changes may well be due to distraction. The same stimuli (in some cases applied for periods of up to 1 h) given prior to the histamine or mustard oil, produced no significant reduction in evoked itch or pain. Noxious stimuli of all types applied 2 min after histamine or mustard oil challenge produced a consistent and significant inhibition of itch (22.8-52.7%) which outlasted the period of counterstimulation application. In contrast, these stimuli had no significant effects on chemically induced pain. The anti-pruritic state produced by brief noxious stimuli were effective for periods of more than 30 min. The differential effects of noxious counterstimuli on itch and pain do not support the suggestion that itch is a subliminal form of pain. Noxious counterstimuli are likely to act via a central rather than peripheral mechanism. The novel finding that a persistent anti-pruritic state can be induced by transdermal constant current may be useful in conditions of clinical itch.

Adult↗