Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REFLEX”

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 901 records · Page 50Linked to original sources
PubMed2002

Methods of H-reflex evaluation in the early stages of Parkinson's disease.

Differentiating the early stages of Parkinson's disease from the normal consequences of aging or from other common neurologic conditions can be diagnostically problematic. The purpose of this study was to compare methodologies for measuring motor neuron excitability of Parkinson's disease patients with a control group. H-reflexes were monitored in 16 patients diagnosed in the early stages of Parkinson's disease (Hoehn & Yahr stages I and II) compared with 30 subjects who were disease free. Methods of measurement included H-reflex latencies, the relative values of maximum H-reflexes to maximum direct motor responses (H-to-M ratio), the relative values of H-reflex amplitudes during vibration compared with control H-reflex amplitudes (Hv-to-Hc ratio), and double-stimulation H-reflex recovery curves using different interstimulus interval parameters. No significant differences were observed for the H-to-M or Hv-to-Hc ratios, or for the H-reflex latencies. The H-reflex recovery curves for the patients with Parkinson's disease demonstrated significantly greater ratio amplitudes than the control group during the double-stimulus responses between the 150-msec and 700-msec interstimulus intervals. Although comparisons of simple H-reflexes and H-reflexes during vibration did not differentiate the patients in the early stages of Parkinson's disease from the control group, the double-stimulation paradigm was a sensitive method for detecting early diagnoses of this disease.

Adult↗
PubMed2001

Excitability of the human trigeminal motoneuronal pool and interactions with other brainstem reflex pathways.

We studied the properties of motoneurones and Ia-motoneuronal connections in the human trigeminal system, and their functional interactions with other brainstem reflex pathways mediated by non-muscular (Abeta) afferents. With surface EMG recordings we tested the recovery cycles of the heteronymous H-reflex in the temporalis muscle and the homonymous silent period in the masseter muscle both elicited by stimulation of the masseteric nerve at the infratemporal fossa in nine healthy subjects. In four subjects single motor-unit responses were recorded from the temporalis muscle. In six subjects we also tested the effect of the stimulus to the mental nerve on the temporalis H-reflex and, conversely, the effect of Ia input (stimulus to the masseteric nerve) on the R1 component of the blink reflex in the orbicularis oculi muscle. The recovery cycle of the H-reflex showed a suppression peaking at the 5-20 ms interval; conversely the time course of the masseteric silent period was facilitated at comparable intervals. The inhibition of the test H-reflex was inversely related to the level of background voluntary contraction. Single motor units were unable to fire consistently in response to the test stimulus at intervals shorter than 50 ms. Mental nerve stimulation strongly depressed the H-reflex. The time course of this inhibition coincided with the EMG inhibition elicited by mental nerve stimulation during voluntary contraction. The trigeminal Ia input facilitated the R1 component of the blink reflex when the supraorbital test stimulation preceded the masseteric conditioning stimulation by 2 ms. We conclude that the time course of the recovery cycle of the heteronymous H-reflex in the temporalis muscle reflects the after-hyperpolarization potential (AHP) of trigeminal motoneurones, and that the Ia trigeminal input is integrated with other brainstem reflexes.

Adult↗
PubMed1982

Motor functions: associated primitive reflex profiles.

The results of reflex/motor activity interactions in 177 normal infants are evaluated. The asymmetrical tonic neck reflex, tonic labyrinthine reflex-supine, and Moro reflexes were assessed for each child at birth and at intervals up to 12 months. Ages of rolling prone to supine, rolling supine to prone, and sitting alone were elicited from parents. The effects of the primitive reflexes on early motor activity were assessed, and statistically significant correlations were demonstrated between decreased reflex activity and the emergence of motor milestones. The distinctive association of reflex activity with motor function suggests the interaction of several reflexes (a primitive reflex profile) rather than the influence of isolated reflex activity. Such patterns support the hypothesis that decreasing primitive reflex activity is associated with the onset of volitional motor activity in normal infants.

Developmental Disabilities↗
PubMed1987

Effects of ischaemia upon reflex electromyographic responses evoked by stretch and vibration in human wrist flexor muscles.

1. The reflex electromyographic responses evoked in a wrist flexor muscle, flexor carpi radialis (f.c.r.), by forcible extension of the wrist ('stretch') and by vibration of the flexor tendon have been studied in normal subjects. Reflexes were elicited during the maintenance of a low level of voluntary flexor contraction (5% maximum). Stretch regularly produced a relatively prolonged (ca. 100 ms duration) increase in e.m.g. activity which was usually divisible into short-latency (ca. 25 ms, M1) and long-latency (ca. 50 ms, M2) peaks. Vibration produced a single, phasic peak, at short latency, with no sign of an accompanying long-latency wave comparable to the M2 stretch response. 2. Ischaemia was induced by inflation of a blood-pressure cuff around the upper arm and its effects upon the reflex patterns were studied. During ischaemia M1 stretch responses showed a more rapid and pronounced decline than did M2 responses and were abolished before voluntary power was appreciably affected. Vibration-evoked short-latency peaks changed in an essentially parallel manner to M1 stretch reflexes. During recovery from ischaemia M2 reflexes were restored before short-latency responses. 3. The patterns of reflex reductions in e.m.g. upon withdrawal of stimulation were also studied. Such troughs in activity, under non-ischaemic conditions, regularly commenced at short latency and were of relatively small amplitude. The records of several of the subjects, and particularly ones obtained during ischaemia, suggested that release of stretch (with concomitant stretch of antagonists) could elicit an additive, long-latency decline in e.m.g. The existence of any such separate, delayed component was never observed upon termination of vibration. 4. Measurements of changes in the latencies and durations of reflex components, accompanying the progression of ischaemia, indicated that depression of early reflex activity resulted in part from increases in the latencies of these initial peaks but predominantly reflected simultaneous and separate reductions in their amplitudes. 5. The generation of short-latency reflexes by stretch and vibration, both of which stimuli powerfully excite muscle spindle primary endings, and the marked susceptibility of these responses to ischaemia supports their being mediated by group Ia afferents. The contrasting behaviour of M2 stretch responses, both regarding their absence with vibration and their resistance to ischaemia, suggests that they depend crucially upon a separate group of reflex afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

Difference in the amplitude of the human soleus H reflex during walking and running.

1. The Hoffman reflex, or H reflex, was strongly modulated in the human soleus muscle during both walking (4 km/h) and running (8 km/h). It was relatively low at the time of heel contact, increased progressively during the stance phase, and reached its maximum amplitude late in the stance phase. During ankle dorsiflexion the H reflex was absent. 2. During running the peak e.m.g. level of the soleus was on average 2.4 times higher than during walking but the maximum amplitude of the H reflex was never larger than during walking. In fact, the H reflex was on average significantly (P less than 0.05 for one-tailed t test) smaller during running than during walking. Furthermore, the slope of the least-squares line fitted to the relation between the H reflex amplitude and the background e.m.g. was always steeper for the walking data than for the running data. 3. The difference in the H reflex in the two tasks is evidence that the size of the H reflex is not simply a passive consequence of the alpha-motoneurone excitation level, as indicated by the e.m.g., but is also influenced by other central neural mechanisms. We suggest that presynaptic inhibition is the most likely mechanism accounting for the change in the slope. 4. The modulation of the reflexes during walking and running can be interpreted in terms of the idea of automatic gain compensation. The decreased gain during running may be appropriate to reduce saturation of motor output and potential instability of the stretch reflex feed-back loop.

H-Reflex↗
PubMed2001

Differential regulation of cutaneous and H-reflexes during leg cycling in humans.

Reflexes undergo modulation according to task and timing during standing, walking, running, and leg cycling in humans. Both cutaneous and Hoffman (H-) reflexes are modulated by movement and task. However, recent evidence suggests that the modulation pattern for cutaneous and H-reflexes may be different. We sought to clarify this issue by reducing the effect of movement phase and altering the level of background muscle activation (low and high) in static and dynamic (leg cycling) conditions. Electromyography was recorded from the ankle extensors soleus and medial gastrocnemius (MG) and the knee extensor vastus lateralis (VL). Reflexes were evoked during the downstroke of stationary leg cycling. Cutaneous reflexes were evoked with trains of 5 x 1.0 ms pulses at 300 Hz delivered to the distal tibial nerve, whereas H-reflexes were evoked in soleus by stimulation with single 1.0-ms pulses. There were two main observations in this study: 1) middle latency cutaneous reflexes were facilitatory during static contraction but were dramatically attenuated or reversed to suppressive responses during cycling (task-dependent modulation); 2) soleus H-reflexes were larger in the high muscle activation condition but were unaffected by task (no task-dependent modulation). Thus opposite results were obtained in the two reflex pathways. It is concluded that cutaneous and H-reflexes are modulated by different mechanisms during active locomotor-like movements.

Adult↗
PubMed1982

[Clinical studies on chaddock reflex].

One hundred neurological cases were evaluated for the positive rates of 6 pathological reflexes by the same examiner (author). Chaddock and Babinski reflexes were highly sensitive, their positive occurrence being 97.1% and 80.3% of the cases respectively, compared with other pathological reflexes. In patients with paresthesia on the soles, cold feet or foot grasping, Chaddock reflex was superior to Babinski, but in some cases Chaddock became definitely positive despite negative Babinski without attributable reasons, suggestive of the former is more sensitive than the latter. The original stimulation site in Chaddock reflex is the skin area just beneath the external malleolus, and within sural nerve distribution. The elicitation of Chaddock reflex was attempted by stimulating the dorsum of the foot from medial to lateral border, with definite positive responses from the areas of sural nerve distribution. To evaluate the sensitivity and receptive field of Chaddock reflex more objectively, the electromyographic method was employed in 13 cases. The needle electrode was inserted into the extensor hallucis longus (EHL) to monitor the up-going toe, as well as flexor hallucis brevis (FHB) for the plantar flexion of the toe, and the surface electric stimulator was applied to 7 different points of the foot and leg, including original Chaddock and Babinski zones. The results of electrical stimulations to 7 different sites revealed that definitely better responses of EHL in sural nerve distribution, compared with other nerve supply. The threshold strength to evoke the action potentials in EHL proved that Chaddock's area was significantly more sensitive than Babinski's area. The relationship of latencies between EHL and FHB on electrical stimulations to the Chaddock's and Babinski's areas showed that earlier and better responses in EHL than in FHB in Chaddock, which could be another reason that Chaddock reflex was more sensitive than Babinski. From the clinical and electromyographic evaluations mentioned above, Chaddock reflex is not just a variant of Babinski reflex, more sensitive and accurate, and its receptive field is considered to be in sural nerve distribution.

Adolescent↗
PubMed1964

NONSPECIFIC DEPRESSANT ACTION OF GAMMA-AMINOBUTYRIC ACID ON SOMATIC REFLEXES.

The effects of gamma-aminobutyric acid (GABA) on central integration of somatic reflexes in the cat have been studied by topical application, and by intrathecal or intracerebroventricular injection. Intrathecal injection of GABA inhibited the monosynaptic patellar reflex. The facilitation of the patellar reflex induced by strychnine, leptazol, tubocurarine and tetanus toxin was also inhibited. Polysynaptic facilitation of the patellar reflex induced in the spinal cat by electrical stimulation of the contralateral sciatic nerve was depressed by intrathecal GABA. Similarly, the supraspinal facilitation of the patellar reflex by electrical stimulation of the brain stem reticular formation was inhibited by application of GABA to the floor of the 4th ventricle. The polysynaptic inhibition of the patellar reflex at both levels was intensified by GABA. The flexor (tibialis anterior) reflex was depressed in the same manner as the extensor patellar reflex. The polysynaptic linguomandibular reflex was depressed by intracerebroventricular GABA. The depressant action of GABA at spinal and supraspinal levels of the neuraxis is discussed in relation to the role of GABA as an inhibitory transmitter in the central nervous system.

Aminobutyrates↗
PubMed1997

Focal subcortical reflex myoclonus. A clinical and neurophysiological study.

BACKGROUND: Patients with progressive myoclonus epilepsy or progressive myoclonus ataxia often show a focal myoclonus, both spontaneous and reflex to somatosensory stimuli. Myoclonus is time-locked to large ("giant") electroencephalographic potentials. Previous authors have classified it as a "cortical reflex myoclonus," with the assumption that it invariably arises from an abnormal corticifugal neuron discharge. OBJECTIVE: To identify the myoclonus source, using various neurophysiological techniques, in 5 patients with progressive myoclonus epilepsy/ataxia. METHODS: Extensive investigations were performed to ascertain the clinical diagnosis. Electrophysiologically, the main method was transcranial cortical stimulation and motor evoked potential measurement. The latency and amplitude of the spontaneous myoclonus and the premyoclonus cortical spike, the reflex myoclonus (C-reflex), and the giant somatosensory evoked potential were also analyzed. The behavior of giant somatosensory evoked potentials and C-reflexes were then studied on single, consecutive trials. Finally, the central motor pathway excitability and its changes attributable to a prior somatosensory input were determined. RESULTS: The motor evoked potential studies showed that the expected corticomuscular conduction time (23 milliseconds) of the myoclonic electromyographic potential was longer than that previously suspected. Considering this, the premyoclonus cortical spike and the giant somatosensory evoked potential were so close to the spontaneous/reflex jerks that they could not reflect a cortical myoclonus source. In 4 patients, the C-reflex latency (< 41.6 milliseconds) was shorter than that often reported in previous studies. The giant somatosensory evoked potential and the C-reflex showed no simple cause-effect link. Motor pathways were hyperexcitable only in response to somatosensory inputs. CONCLUSIONS: The data pointed to a cortical myoclonus origin only in the patient whose C-reflex had the longest latency (44 milliseconds). In the remaining patients, a subcortical source was far more likely. In this group of patients, cortical stimulation disclosed a new myoclonus variety, for which the term focal subcortical reflex myoclonus is proposed; it mimics cortical reflex myoclonus but has a shorter latency.

Action Potentials↗
PubMed1999

Prolonged sympathetic reflex latency on skin nerves in sporadic cerebellar degeneration.

BACKGROUND: Many physiological or pharmacological evaluations of autonomic function have been performed in patients with various types of cerebellar degeneration (CD). Few studies have been done, however, using neurographic recordings in patients with CD, especially of sudomotor or vasoconstrictor nerves. OBJECTIVE: To confirm the clinical importance of sympathetic reflex latencies on the skin nerves of patients with various types of CD. DESIGN AND SETTING: Case-comparison study at an academic center. PARTICIPANTS: We studied 12 patients who had sporadic CD (cerebellar cortical atrophy, olivopontocerebellar atrophy, and Shy-Drager syndrome) and 15 healthy volunteers as controls. METHODS: Skin sympathetic nerve activity (SSNA), sympathetic skin response, and skin vasomotor reflex were simultaneously recorded using randomly administered electrical stimuli. RESULTS: In controls, SSNA reflex latency ranged from 640 to 864 milliseconds. Patients with cerebellar cortical atrophy exhibited slight but significant (P<.01) prolongation of reflex latency to the onset of reflex bursts. In patients with olivopontocerebellar atrophy, latency to the onset and the peak of reflex bursts was significantly prolonged (P<.001). Patients with Shy-Drager syndrome had no SSNA, sympathetic skin response, or skin vasomotor reflex, even with supramaximal electrical stimuli. CONCLUSIONS: Prolonged reflex latency or the absence of reflex bursts on SSNA can be observed in patients with CD with various forms of autonomic dysfunction. The measurement of SSNA reflex latency may be a useful method of evaluating sympathetic function, including the central pathway.

Aged↗
PubMed2002

Is the cutaneous silent period an opiate-sensitive nociceptive reflex?

In humans, high-intensity electrical stimuli delivered to the fingers induce an inhibitory effect on C7-T1 motoneurons. This inhibitory reflex, called the cutaneous silent period (CSP) is considered a defense response specific for the human upper limbs. It is not clear whether the CSP-like other defense responses such as the corneal reflex and the R III reflex-is an opiate-sensitive nociceptive reflex. Because opiates suppress some, but not all, nociceptive reflexes, we studied the effect of the narcotic-analgesic drug fentanyl on the CSP and the R III reflex. The CSP was recorded from the first dorsal interosseous (FDI) muscle in seven normal subjects during voluntary contraction, before and 10 and 20 min after fentanyl injection. To assess possible fentanyl-induced changes, we also tested the effect of finger stimulation on motor evoked potentials (MEPs) elicited in the FDI muscle by transcranial magnetic stimulation before and after fentanyl injection. Fentanyl-induced changes were also studied on the R III reflex recorded from the biceps femoris muscle. Fentanyl, as expected, suppressed the R III reflex but failed to change the inhibitory effect of finger stimulation on FDI motoneurons. Finger stimulation reduced the size of MEPs in the FDI, and fentanyl injection left this inhibitory effect unchanged. The differential fentanyl-induced modulation of the CSP and R III reflex provides evidence that the CSP circuit is devoid of mu-opiate receptors and is therefore an opiate-insensitive nociceptive reflex, which may be useful in the assessment of central-acting, non-opioid drugs.

Adult↗
PubMed1995

Homonymous and heteronymous monosynaptic reflexes in biceps brachii.

Using poststimulus time histograms, it has been reported that stimulation of the median nerve at the elbow produces a monosynaptic EPSP in voluntarily active single motoneurons of the human biceps brachii. The present study was undertaken to: (i) determine whether such stimulation could evoke a reproducible reflex response in biceps brachii; and (ii) establish the optimal conditions for eliciting the reflex under clinical conditions. Twelve normal subjects were studied. No reflex response was recordable when biceps brachii was relaxed. A reflex response with a mean latency of 14.0 ms (+/- 0.96 ms) could be recorded during a background voluntary contraction. The response was small (0.5-4.5% of the maximal M wave) but symmetrical, and could be obtained in all subjects. The responsible afferents appear to be rapidly conducting fibers from forearm flexor muscles and the latencies of the response were consistent with a monosynaptic reflex. Reflex amplitude increased with stimulus intensity and contraction strength. Stimulus rate did not affect amplitude significantly. It is concluded that a reproducible heteronymous monosynaptic reflex can be recorded from the contracting biceps brachii on stimulation of the median nerve at the elbow. Although smaller than the homonymous H reflex evoked by stimulation at Erb's point, it was technically easier to demonstrate that the EMG potential was of reflex origin (rather than part of an M wave). These reflexes should be of value in the assessment of the C-5/C-6 segments and the upper trunk of the brachial plexus.

Adult↗
PubMed1993

Gain and threshold of the jaw-jerk reflex in man during isometric contraction.

The control of mandibular posture has been related to the activity of the anterior temporal muscles, whereas the masseter muscles have been viewed mainly as force producers. However, these groups of muscles, especially in the deep layers, are highly endowed with muscle spindles, so that a difference in function should imply a difference in the reflex sensitivity. By studying the jaw-jerk reflex by means of bipolar surface electromyogram, the reflex sensitivity was determined from relationships between reflex amplitude and jaw displacement from both groups of muscles in eight subjects. At a constant level of background muscle activity, and hence with a constant excitability of the alpha motoneurons, the reflex sensitivity can be determined from these relationships in terms of gain and threshold. In order to account for differences in thickness of the soft tissues overlying the various muscles studied, the reflex amplitude was normalized with respect to the level of maximal voluntary contraction (MVC). In experiments where the inter-electrode distance was 18 mm over both groups of muscles, the reflex gain of the anterior temporal muscles was larger than that of the masseter muscles (P < 0.05). The threshold value did not differ significantly from zero for either group of muscles. Normalization of the reflex amplitude with respect to MVC can be carried out correctly only if the reflexly activated muscle fibres are distributed uniformly within the muscle. In order to gain an insight into this distribution, control experiments were performed with three subjects in which the inter-electrode distance was varied, thus influencing the depth in the muscle from which active muscle fibres were recorded. The reflex gain of the masseter muscle with an inter-electrode distance of 22 mm, which records from deeper layers of the muscle as well as superficial ones, was larger than with a distance of 11 mm (P < 0.01-0.10 in the various subjects). No such differences were found for the anterior temporal muscle. It was concluded that the afferents of the spindles in the jaw-elevator muscles do not project uniformly upon the motoneurons, but involve mainly fibres in the deeper layers of the muscle. The difference in gain found between the masseter and the anterior temporal muscles with the same inter-electrode distance of 18 mm is likely to be due to a larger distance of the reflexly activated muscle fibres in the masseter muscle with respect to the electrodes rather than to a difference in reflex sensitivity between the muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1993

Identification of time-varying dynamics of the human triceps surae stretch reflex. II. Rapid imposed movement.

We examined the time-varying dynamics of the human triceps surae stretch reflex before, during, and after a large stretch was imposed upon the ankle joint, during a constant voluntary contraction of 15% of maximum voluntary contraction. Stretch reflex dynamics were estimated by superimposing a small stochastic displacement on many such stretches and using an "ensemble-based" time-varying identification procedure to compute impulse response functions relating the perturbation to the evoked electromyogram (EMG) at each point throughout the task. We found that stretch reflex magnitude (relating joint velocity to EMG) varied directly with baseline EMG activity during steady-state conditions before and after the large imposed stretch. Following the large stretch and the reflex activity it evoked, both background EMG and stretch reflex magnitude declined for up to 100 ms; changes in the stretch reflex were substantially greater in magnitude and followed a different time course from the corresponding changes in background EMG, however, indicating that stretch reflex properties were modulated independently of motoneuron pool activation level. Based on timing and the invariance of stretch reflex dynamics across time, it is argued that this behavior is largely mediated via peripheral neural mechanisms. This peripheral modulation of the stretch reflex presumably supplements various descending influences to adjust reflex properties.

Adult↗
PubMed1995

Effect of reversible dorsal cold block on the persistence of inhibition generated by spinal reflexes.

The effects of bilateral focal cooling of dorsolateral thoracic spinal cord on segmental reflex pathways to the triceps surae muscles were assessed in decerebrate cats from the reflex forces produced by single shocks or trains of electrical stimuli applied to the ipsilateral caudal cutaneous sural and the contralateral tibial nerves. The validity of the dorsal cold block technique as a substitute for acute surgical dorsal hemisection was established by showing that focal cooling reliably reproduced the stretch-induced "clasp knife" inhibition of triceps surae reflexive force seen following dorsal hemisection. Under control (warm) conditions, the inhibitory components of electrically evoked ipsilateral sural and contralateral tibial reflexes faded rapidly during sustained trains, with a resultant production of large-amplitude reflex force as measured from either the entire triceps surae or from the medial gastrocnemius muscle alone. Dorsal cold block greatly reduced the amplitude of reflexive force evoked by sustained electrical stimulation of either nerve. Indeed, the cold block completely reversed the sign of train-evoked reflexes to a net inhibition of reflex force output in one-half of the sural and one-half of the contralateral tibial stimulation experiments. Peak transient forces evoked by single shocks to the sural or contralateral tibial nerves were also sometimes reduced, but this result was more variable than for prolonged nerve stimulation. The persistence of activity in segmental inhibitory pathways during dorsal cold block, as indicated by instances of reflex sign reversal, suggests that descending bulbospinal pathways traversing the dorsolateral funiculi may be responsible for "fading" of segmental inhibitory reflex components in decerebrate cats with intact spinal cords during sustained afferent input. The possibility that the enhanced magnitude and duration of segmental inhibition during cold block will increase the likelihood of disruption of the size principle for motoneuron recruitment is also discussed.

Animals↗
PubMed1980

The dynamic neck-eye reflex in mammals.

Stimulation of cervical proprioceptors by torsion of the neck results in movement of the eyes. The pathways of this neck-eye reflex have been identified electrophysiologically, and in individuals with vestibulo-ocular deficits the reflex is often seen to contribute to retinal image stability during head movements. In intact individuals, however, its role in ocular compensation for head movements is questionable. In this and other studies, the reflex eye movements were in the direction opposite the vestibulo-ocular reflex and were, therefore, anticompensatory. In four species of mammal (rat, rabbit, cat, and bush baby - a primate), the reflex was most consistently elicited with an anticompensatory phase; furthermore, when an animal partially stabilizes its head in space (by the vestibulo-collic reflex) during body rotation, the vestibulo-ocular and neck eye reflexes must have opposite polarities if their summation is to be of use to the animal. The neck-eye reflex appears to be absent when the animal actively moves its head; it only appears during the experimental procedure employed to elicit the reflex. An alternative function for the electrophysiologically identified pathway of the neck-eye reflex is suggested.

Animals↗
PubMed1989

Specific modulation of the Hoffmann reflex cutaneous facilitation during a reaction-time task.

The Hoffmann (H) reflex and its facilitation produced by electrical stimulation of the sural area were examined before a ballistic extension of the right foot. Modulations of the cutaneous facilitation of the H reflex (CFH) were used to assess the control exerted over the transmission of low threshold cutaneous afferents. The time-course of H and CFH changes were investigated at the end of the foreperiod and during the premotor period, i.e. between the response signal and the onset of the electromyogram (EMG) of the soleus muscle. Four stimulation conditions were set up depending on whether the H reflex was elicited on the contracting or non-contracting limb, and whether cutaneous stimulation was ipsilateral or contralateral to the reflex. During the 100 ms preceding the response signal, the inhibition of the H reflex was more marked in the contracting limb than in the non-contracting limb. At the end of the foreperiod, the CFHs had a symmetric time course: the CFHs evoked by conditioning stimulation of the contracting limb were facilitated just before the response signal, while those produced by conditioning stimulation to the non-contracting limb were depressed. It is suggested that these variations are related to postural adjustments taking place before the movement is performed. As previously reported, the H reflex of the contracting limb exhibited a marked increase in amplitude over the 50 ms preceding the EMG. Reflex facilitations showed specific variations according to the ankle stimulated and the soleus muscle tested. The CFHs produced by stimulation of the non-contracting limb regained, at the end of the premotor period, a value close to their reference level recorded in trials without movement. The CFHs, produced by conditioning stimulation of the contracting limb were modulated differently according to whether the tested soleus muscle was contracting or not: when the CFH was tested on the contracting muscle, it was found to be depressed throughout the premotor period; this contrasted significantly with the isolated depression recorded on the non-contracting muscle. Therefore, only the cutaneous afferents from the mobilized limb, modulating the H reflex of the same limb, were subject to a specific inhibition during the premotor period. Throughout the preparatory and premotor periods, negative correlations were observed between H and CFH amplitude, except just before the EMG onset in the condition where the H reflex was delivered to the contracting muscle and the cutaneous stimulation to the ankle of the non-contracting limb: in this case, CFH amplitude increase paralleled that of the reflex amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1995

Distal rectoanal excitatory reflex: a reliable index of pudendal neuropathy?

PURPOSE: Denervation of the extrinsic anal sphincter and pudendal neuropathy are confirmed by electrophysiologic or electromyographic testing, techniques that may not be available universally and require special equipment and training. A simple manometric test that is easy to perform and complements existing studies was performed to confirm pudendal neuropathy. METHODS: Fourteen patients with excessive defecatory straining and 30 patients with idiopathic fecal incontinence were studied by electrophysiology and balloon reflex manometry. Pudendal nerve terminal motor latency (PNTML) and rectoanal excitatory reflex were evaluated for abnormalities. Results were compared with 20 controls who had no anorectal complaints and who had similar testing performed. RESULTS: In controls, PNTML was normal in all but one person. Rectoanal excitatory reflex could be elicited in all controls with either 20 or 40 ml of air. Four different types of balloon reflex responses were observed in patient groups: diminutive excitation, delayed excitation, excitation at high volume of distention only, and absent excitation. Ten patients with fecal incontinence had normal PNTML but abnormal distal excitatory reflex, 5 patients had abnormal PNTML but normal distal excitatory reflex, and 15 patients had both PNTML and excitatory reflex that were abnormal. In patients with excessive defecatory straining, results of both tests were abnormal in six patients, and eight patients had abnormal excitatory reflex but normal PNTML. CONCLUSION: Pudendal neuropathy may result in abnormalities of excitatory reflex morphology or other characteristics. Abnormal distal excitatory reflex may complement electrophysiologic findings or may serve as a suitable alternative to confirm pudendal neuropathy in centers where facilities for formal testing are not available.

Adult↗