Amplitude Of Motor Response Research Articles

Évaluation électrophysiologique des nerfs crâniens moteurs (V, VII, IX, X, XI, XII)

In various neurosurgical operations, there is a risk of cranial nerve lesion that can be avoided or minimized with intraoperative electrophysiological monitoring. Regarding motor function of the cranial nerves, stimulodetection techniques are used, including electrical stimulation of nerve trunks and electromyographic recording of evoked motor responses. These techniques can be used for monitoring the trigeminal nerve (Vth cranial nerve), facial nerve (VIIth), glossopharyngeal nerve (IXth), pneumogastric nerve (Xth), spinal accessory nerve (XIth), and hypoglossal nerve (XIIth), in particular during surgical removal of tumors of the cerebellopontine angle or skull base. When beginning an operation, electrical stimulation is only used to identify the nerve structures. As removal of the tumor progresses, the goal is to verify that a surgical injury to the nerve is avoided by looking for the absence of any change regarding amplitude, morphology, and latency of motor responses. Intraoperative electromyographic monitoring can also be applied during the surgical treatment of primary hemifacial spasm by microvascular decompression. An effective decompression is usually associated with the disappearance of "lateral spread" motor responses to facial nerve branch stimulation. Therefore, the intraoperative disappearance of the lateral spread responses can be considered a predictive factor of good postoperative clinical outcome, even if this assertion remains a matter of debate.

The Potential Benefit of Intracarpal Pressure Measurement in Endoscopic Carpal Tunnel Syndrome Surgery – An Analysis of EMG Findings and Pressure Values

Endoscopic carpal tunnel syndrome surgery is a modern minimally invasive method of carpal tunnel decompression. However, the method does also have its critics, who emphasize that there is an increased rate of complications in comparison to open procedures. To further improve and optimize results of endoscopic surgery we used an intracarpal pressure sensor to verify the effect of carpal tunnel decompression. The endoscopic single portal approach was used in all cases. Median nerve conduction studies were performed prior to and 3 months after surgery. Two groups, those with pressure studies and those without, were then compared according to several EMG parameters such as: median nerve distal motor latency, amplitude of motor response, sensory nerve conduction velocity to the index finger, and amplitude of sensory nerve action potential. In both groups, we observed similarly significant improvements in all conduction parameters, except the amplitude of motor response, which did not change in either group, i.e. no difference in postoperative EMG between the two groups was observed. Despite this fact, intracarpal pressure measurement is still useful in localising the point in which the median nerve is compressed and provides valuable functional information on the level decompression achieved.

Quantitative application of transverse friction massage and its neurological effects on flexor carpi radialis

The purpose of the study was to determine the effects of transverse friction massage (TFM) on flexor carpi radialis (FCR) motoneuron (MN) pool excitability. Twenty-eight healthy subjects were randomly assigned into massage and control groups. Pre- vs post-TFM H-reflex data were collected. Controls received a rest period instead of massage. Massage dose was standardized by a novel electronic method which recorded the massage rate, momentary pressure and total cumulative pressure (energy). Two-way ANOVA of H/M ratios derived from maximal amplitudes of Hoffman reflexes (Hmax) and motor responses (Mmax) was used to analyze neurological effects and group differences. Analysis of pressure/time curve data showed: mean massage rate was 0.501 ± 0.005 Hz; mean duration of massage sessions was 184.6 ± 26.4 s; mean peak pressure was 4.990 ± 1.006 psi. Hmax/Mmax ratios declined from 14.3% to 10.3% for massage ( P < 0.01) but showed no change for controls ( P > 0.05). In conclusion a novel quantitative approach to the study of massage has been demonstrated while testing the effects of TFM on FCR MN pool excitability. TFM appears to reduce MN pool excitability. The novel method of quantifying massage permits more rigorous testing of client-centered massage in future research.

Effect of intense muscle exercise on motor responses to magnetic stimulation of the brain and spinal cord

The parameters of evoked motor responses of the muscles of the upper and lower extremities to magnetic stimulation of the motor zones of the cerebral cortex, spinal segments, and n. tibialis were estimated in athletes adapted to performance of different duration and intensity (short-and long-distance runners) and having different sports qualifications. It was shown that the maximum amplitude of event-related motor responses of m. gastrocnemius med. and m. soleus to transcranial magnetic stimulation of the brain was higher in the group of long-distance runners as compared with short-distance runners. Ski racers of high qualification differ from less qualified skiers in lower thresholds of excitation and a higher maximum amplitude of evoked motor responses of m. carpi radialis, m. biceps brachii, m. gastrocnemius med., and m. soleus. No statistically significant differences were found between the tested groups of subjects in the time of central motor transmission or the latent period of evoked motor responses.

The Sensitivity of Motor Response to Needle Nerve Stimulation During Ultrasound Guided Interscalene Catheter Placement

Neurostimulation during single shot interscalene block has a significant false negative motor response rate. Compared with tangential needle approaches for single shot block, interscalene catheter (ISC) placement commonly involves Tuohy needles inserted longitudinally to the brachial plexus. This study aimed to determine the sensitivity of neurostimulation during ultrasound-guided ISC needle placement, and the feasibility of an ultrasound-guided ISC needle endpoint. One hundred fifty-five consecutive nonstimulating ISCs were placed with the needle tip position confirmed by the sonographic spread of 5 mL dextrose 5%. Catheter advancement was then blind 2 to 3 cm past the needle tip. A 0.8 mA electrical stimulus at 2 Hz was applied throughout. When a satisfactory image was obtained, neurostimulation was ignored and the minimum motor response amplitude noted. If imaging was equivocal, a brief appropriate motor response at 0.8 mA was sought. A sustained response at <0.5 mA was only sought if imaging was suboptimal. Prior to surgery conducted under general anesthesia, 30 mL ropivacaine 0.5% was administered through the ISC. Catheter success was defined as a recovery room numerical rating pain score of </=2 (scale, 0-10). In 57% of patients, a muscle response was not elicited. An ultrasound needle endpoint was used in 92% of ISC placements, of which 96% were successful. Sustained twitches at <0.5 mA were obtained in 12 (8%) patients, 6 (4%) of these deliberately sought because of suboptimal imaging. Catheter success overall was 95%. This study suggests that the false negative motor response rate for longitudinal ISC needle placement is higher than the false negative response rate associated with tangential needle approach interscalene block. An ultrasound guided ISC needle endpoint is a feasible alternative to a neurostimulation endpoint.

EXPERIMENTATION AND INNOVATION IN FAMILY MEDICINE RESIDENCY EDUCATION: THE TIME IS NOW

<h3>Abstract</h3> The aim of this study was to investigate whether indirect upper limb vibration (ULV) modulates transmission along spinal and corticospinal pathways that control the human forearm. All measures were assessed under CONTROL (no vibration) and ULV (30 Hz; 0.4 mm displacement) conditions while participants maintained a small contraction of the right flexor carpi radialis (FCR) muscle. To assess spinal pathways, Hoffmann reflexes (H-reflexes) elicited by stimulation of the median nerve were recorded from FCR with motor response (M-wave) amplitudes matched between conditions. An H-reflex conditioning paradigm was also used to assess changes in presynaptic inhibition by stimulating the superficial radial (SR) nerve (5 pulses at 300Hz) 37 ms prior to median nerve stimulation. Cutaneous reflexes in FCR elicited by stimulation of the SR nerve at the wrist were also recorded. To assess corticospinal pathways, motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation of the contralateral motor cortex were recorded from the right FCR and biceps brachii (BB). ULV significantly reduced H-reflex amplitude by 15.7% for both conditioned and unconditioned reflexes (24.0±15.7 vs 18.4±11.2 % M_max; <i>p</i>&lt;0.05). Middle latency cutaneous reflexes were also significantly reduced by 20.0% from CONTROL (−1.50 ± 2.1 % Mmax) to ULV (−1.73 ± 2.2 % Mmax; <i>p</i>&lt;0.05). There was no significant effect of ULV on MEP amplitude (<i>p</i>&gt;0.05). Therefore, ULV inhibits cutaneous and H-reflex transmission without influencing corticospinal excitability of the forearm flexors suggesting increased presynaptic inhibition of afferent transmission as a likely mechanism. A general increase in inhibition of spinal pathways with ULV may have important implications for improving rehabilitation for individuals with spasticity (SCI, stroke, MS, etc).

Longitudinal study of the motor response to levodopa in Parkinson's disease

In this prospective study of 34 patients with Parkinson's disease, measurements of the short duration levodopa motor response have been performed in defined off states at 3 yearly intervals over a mean period of 11.4 years from the point of commencement of levodopa treatment. Twenty-two patients were still available for study; 10 had died and 2 were lost to follow-up. The levodopa motor response amplitude increases over the first 5 years of treatment, and thereafter, on and off scores worsen in parallel with conservation of the response. Patients who developed motor fluctuations within the first 5 years of treatment had, on average, a stronger response to levodopa with significantly better on phase motor function (P = 0.003). Although the proportion of "midline" motor disability (affecting gait, balance, and cranial motor function) increases with time, these deficits do not actually become unresponsive to levodopa. Patients who developed dementia had a significantly more rapid decline in motor function. The latest graph of serial scores for the whole cohort shows an upward curving or exponential increase in motor disability after the first decade of treatment. Applying a notional untreated disability line to this graph--an estimate of the disability that would have accrued if drugs had never been given--we suggest that the long-duration response to levodopa eventually runs down with disease progression.

Encephalopathy and peripheral neuropathy following diethylene glycol ingestion

The authors report a 24-year-old man who developed encephalopathy and rapid quadriplegia following ingestion of a solution containing diethylene glycol (DEG). As quadriparesis evolved, motor response amplitudes were markedly reduced with preserved conduction velocities. Studies during clinical recovery revealed marked motor conduction velocity slowing and prolonged distal latencies. These data indicate that DEG intoxication may cause a primary acute axonal sensorimotor polyneuropathy with demyelinating physiology during recovery.

Related timing for peripheral and central plasticity in hypoglossal–facial nerve anastomosis

The aim of this work was to determine the role of peripheral facial muscle reinnervation in the central reorganization of the blink reflex (BR) after hypoglossal-facial anastomosis (HFA). An electrophysiological study was performed on seven patients who underwent HFA after facial nerve transection during surgery for acoustic neuroma. HFA was performed within 15 days after surgery in five patients (group 1) and later for the two others (group 2). We studied the motor responses (MR) and the BR evoked on the affected side, before and over 3 years after the HFA. The MR appeared by the third month for the first group, and by the sixth and twelfth for the second group. After 36 months, the amplitude of MR was significantly higher than its control value, showing hyperinnervation of the facial muscles. Study of the BR evoked only an R1-type blink response that was observed 4 and 6 months after the MR for groups 1 and 2, respectively. This central reorganization appeared closely correlated with muscle reinnervation and its related timing. The occurrence of peripheral nerve-muscle contacts seems to be a necessary condition for reorganization of the trigemino-hypoglossal-facial reflex.

Intra- and Intersubject Reliability of Abductor Pollicis Brevis Muscle Motor Map Characteristics With Transcranial Magnetic Stimulation

Corneal SF, Butler AJ, Wolf SL. Intra- and intersubject reliability of abductor pollicis brevis muscle motor map characteristics with transcranial magnetic stimulation. Objective To determine consistency in motor maps of the abductor pollicis brevis (APB) muscle using transcranial magnetic stimulation (TMS) with conventional and close-spaced surface electrode recording placements. Design Nonrandom convenience sample. Setting TMS laboratory. Participants Eleven participants without any known neurologic disorders. Interventions The left hemisphere of right-hand-dominant subjects was mapped using TMS at each of 2 sessions, separated by 1 to 8 weeks. Main Outcome Measures Measurements at each session included the resting motor threshold, active site locations and average motor response amplitude for active sites, normalized map volume, and center of gravity (COG) for both electrode array configurations. Results The normalized map volume was larger for the conventional electrode placement than for the close electrode placement (4.23cm 2 vs 3.44cm 2, P=.010). Resting motor threshold was higher for the close-spaced than for the conventional-spaced electrodes (48.36% vs 46.59%, P=.028). No statistical difference was found between sessions and within electrode placements for the normalized map volume, for resting motor threshold, or for the mean motor amplitude of the most active site for each map. No statistical difference was observed for the COG distance between electrode placements. Conclusions This study revealed differences between close-spaced and conventional-spaced surface electrode placement for TMS motor map volumes and for resting motor thresholds. The motor maps for the APB muscle were reliably reproducible between sessions for each electrode array.

New criteria for early electrodiagnosis of acute inflammatory demyelinating polyneuropathy

A variety of electrodiagnostic methods are used to confirm the diagnosis of acute inflammatory demyelinating polyneuropathy (AIDP), but difficulties are frequent during the first few weeks of weakness. We compared the nerve conduction studies (NCS) of patients with AIDP to those with critical illness polyneuropathy (CIP), a subacute axonal polyneuropathy. New electrodiagnostic criteria with graded certainty (normal, nondiagnostic, suggestive, highly suggestive, and definite) were designed and applied in a blinded manner to both groups. Among the AIDP patients, 64% met the highly suggestive and definite criteria (specificity 95-100%, P < 0.01), whereas 80% of the CIP group fell in the nondiagnostic criteria (P < 0.001). The relative preservation of the sural sensory response in spite of at least two abnormal sensory NCS in the upper limb suggested acute demyelination (sensitivity 48%, specificity 96%, P < 0.001) and was even more conclusive when associated with absent or prolonged F waves. Motor and sensory response amplitudes were lower in the CIP group, with comparable mean motor and sensory distal latencies and motor conduction velocities. Motor conduction blocks were present in 10% of nerves in AIDP and were not encountered in CIP. The frequency of absent or delayed F waves and absent H reflex was similar in both groups. The correlation coefficient of the cerebrospinal fluid protein concentration with the designed criteria was higher in the AIDP group (r = 0.9). We conclude that a new criterion with graded certainty is of higher specificity in the majority of patients with early AIDP.

Encephalopathy and peripheral neuropathy following diethylene glycol ingestion

The authors report a 24-year-old man who developed encephalopathy and rapid quadriplegia following ingestion of a solution containing diethylene glycol (DEG). As quadriparesis evolved, motor response amplitudes were markedly reduced with preserved conduction velocities. Studies during clinical recovery revealed marked motor conduction velocity slowing and prolonged distal latencies. These data indicate that DEG intoxication may cause a primary acute axonal sensorimotor polyneuropathy with demyelinating physiology during recovery.

The Cerebellum Modulates Rodent Cortical Motor Output after Repetitive Somatosensory Stimulation

To analyze the possible role of the cerebellum in the modulation of cortical motor output associated with repetitive electrical stimulation of the sciatic nerve in the rat. A sustained somatosensory stimulation induces an increase in the intensity of the response of the rodent motor cortex. Wistar rats were anesthetized for surgical preparation using a continuous infusion of chloral hydrate. We analyzed the response evoked by electrical stimulation of the right motor cortex before (basal condition) and after peripheral electrical stimulation of the left sciatic nerve in rats with no cerebellar intervention (n = 6), and in control rats with Ringer's infusion via a microdialysis probe (n = 8) implanted in the left cerebellar nuclei. In addition, we investigated the effects of 1) the administration of ethanol (20 mmol/L) in the left cerebellar nuclei (n = 5); 2) the administration of tetrodotoxin (10 micromol/L), a sodium channel blocker, in the left cerebellar nuclei (n = 5); 3) electrical stimulation by deep cerebellar stimulation (frequency 100 Hz) on the left side (n = 5); or 4) electrical stimulation of the cerebellar nuclei on the right side (100 Hz; n = 6). For peripheral stimulation, all of the animals received 1 hour of electrical stimulation. Trains of stimulation consisted of five stimuli (duration of 1 stimulus, 1 ms) at a rate of 10 Hz. During stimulation of the motor cortex, peak-to-peak amplitudes in responses of the left calf muscle were analyzed. Motor threshold was defined as the lowest intensity eliciting at least 5 of 10 evoked responses with an amplitude greater than 20 muV. The intensity used was 130% of the motor threshold. In the basal condition (before repetitive stimulation), amplitudes of motor responses were similar in the six groups of rats (P = 0.40). In rats without cerebellar intervention, peripheral electrical stimulation was associated with an increase of motor response to 147.4 +/- 8.5% of baseline (P < 0.001). In rats with Ringer's infusion, the motor response increased to 141.6 +/- 7.9% of baseline (P < 0.001). The administration of ethanol in the cerebellum prevented the enhancement of the response ipsilaterally. The mean +/- standard deviation (SD) of motor responses was 105.7 +/- 6.2% of baseline measurements after stimulation of the sciatic nerve (P = 0.36). The same observation was made after the infusion of tetrodotoxin (mean +/- SD of motor responses: 107.1 +/- 7.4% after peripheral stimulation [P = 0.19] and after electrical stimulation of the cerebellum on the left side [mean +/- SD of motor responses, 104.3 +/- 8.5% after peripheral stimulation, P = 0.40]). However, electrical stimulation of cerebellar nuclei on the right side did not impair the modulation of cortical motor output by sciatic nerve stimulation (mean +/- SD of motor responses, 148.4 +/- 5.8% after peripheral stimulation, P < 0.001). Until now, the increase of motor output after peripheral nerve stimulation has been considered as a plasticity directly and solely dependent on cortical structures. We demonstrate that the cerebellum plays a key role in this form of neural plasticity.

The acute effects of glycemic control on nerve conduction in human diabetics

Objective To investigate acute changes in nerve conduction associated with glycemic control. In diabetes, nerve dysfunction can result from reversible metabolic factors associated with hyperglycemia, as well as structural changes. Methods Multiple nerve conduction parameters including F-wave latencies were measured in 47 diabetic patients with prominent hyperglycemia before and after intensive insulin treatment. Results Four weeks after the start of treatment, there was a significant improvement in minimal F-wave latencies of the median ( P<0.001) and tibial ( P<0.001) nerves, and in distal latencies ( P=0.01) and sensory nerve conduction velocities ( P<0.001) of the median nerves. Amplitudes of motor and sensory responses did not change significantly. These findings were similar for patients with type 1 ( n=8) and those with type 2 ( n=39) diabetes. Patients with poorer glycemic control or milder neuropathy tended to show greater changes after treatment. Conclusions Glycemic control quickly alters the speed of nerve conduction. F-wave latencies and conduction times across the carpal tunnel are very sensitive parameters. Significance Serial nerve conduction studies can detect reversible slowing of nerve conduction presumably caused by metabolic factors, such as decreased Na +/K +-ATPase activity, the altered polyol pathway, and tissue acidosis.

Hipotonía mixta, regresión neurológica y atrofia cerebelosa: manifestaciones sugestivas de distrofia neuroaxonal infantil

Infantile neuroaxonal dystrophy (INAD), or Seitelberger disease, is a neurodegenerative disease of unknown origin which is transmitted by autosomal recessive inheritance. Clinically, it courses with psychomotor stagnation and regression that begins at the age of one or two years, associated to hypotonia with mixed clinical features (segmentary and suprasegmentary) that progresses towards spastic tetraplegia and progressive optic atrophy and dementia; this leads to death before the age of ten years. AIMS. To present the case of a 30 month old child with INAD, in whom a N acetylgalactosaminidase deficiency and mitochondrial cytopathy were ruled out. Male aged 30 months with an initial overall retardation, and later regression, of psychomotor acquisitions. In the physical exploration the patient displayed serious neurological involvement with mixed hypotonia, muscular hypotrophy with generalised weakness and mild bilateral horizontal nystagmus. Complementary explorations with neuroimaging revealed a slight increase in the subarachnoid space, with atrophy of the vermis and cerebellar hemispheres. Neurophysiological tests (EMG and ENG), which were initially normal, later showed signs of denervation in the EMG, and the ENG revealed a decreased amplitude of motor responses, with preservation of conduction speed. Histological tests showed the presence of axons with axoplasm expanded by the inclusion of typical tubulovascular structures. The clinical features of our patient met all the criteria to satisfy a diagnosis of INAD, and he displayed a classic form of the disease. INAD must be considered when the clinician is faced with: 1. A clinical picture of stagnation and later regression of psychomotor development before the age of two years; 2. Hypotonia, muscular atrophy and initial overall areflexia, with later progression towards pyramidalism; 3. Initially normal EMG findings, with later signs of denervation; 4. Cerebellar atrophy (hemispheres and vermis); 5. Visual deficit, and 6. Histopathological proof of characteristic findings.

Diabetes, peripheral neuropathy, and old age disability.

The purpose of this study was to determine whether peripheral neuropathy explains the apparent association between diabetes and disability in old age, and to evaluate the utility of lower extremity function tests in older diabetic adults with and without neuropathy. We evaluated 39 adults, aged 70-79 years, for pressure sensation (log(10)g), vibration perception threshold (VPT; microns), and electrophysiologic function of the peroneal nerve. The subjects included patients with established diabetic neuropathy (DN; n = 14), diabetic controls without neuropathy (DC; n = 13), and nondiabetic controls (NDC; n = 12). Nonparametric statistical methods were used to relate neuropathy measures to performance in tests of walking speed, static and dynamic balance, coordination, and ankle strength (kilograms). Significant age-adjusted correlations were observed between measures of sensory neuropathy and a variety of performance measures, and electrophysiologic measures were related to static balance. DN subjects had significantly higher pressure sensation than NDC (5.17 vs 3.38g, P < 0.05), higher VPT (62.5 vs 21.7 microm, P < 0.05), and lower peroneal motor response amplitudes at multiple sites. Pressure sensation and nerve conduction measures did not differ between DC and NDC. Compared with NDC, DN subjects performed significantly worse on tests of walking speed (0.99 vs 1.34 m/s; P < 0.05), static balance (4.9 vs 20.4 s; P < 0.05), dynamic balance (9.23 vs 25.52 s; P < 0.05), and coordination (6.73 vs 4.76 s; P < 0.05). No differences were observed in these measures between DC and NDC. Observed differences in physical abilities between older diabetic and nondiabetic adults may have been due to the subset of diabetic individuals with peripheral neuropathy. Quantitative measures of sensory and motor nerve function have distinct effects on physical performance. Interventions aimed at reducing the impact of diabetes-associated disability in old age may have the greatest impact among people with peripheral neuropathy.

Influence of age and height on nerve conduction.

Previous studies demonstrated age- and height-related slowing of nerve conduction velocity (NCV) and reduction in nerve response amplitude. Unfortunately, many studies examined discontinuous populations, preventing regression analysis. The correlation coefficients of available studies vary widely, preventing clear conclusions. We retrospectively examined 3969 clinically normal subjects ranging in age from 20 to 95 years from a total of 22,420 electrodiagnostic studies done between 1986 and 1998. The correlation of NCV with height was stronger than with age. Regression equations using both factors account for 12--27% of the variance. Responses were seen in the majority of patients aged 70 years and older, but the percentage of normals who had no response increased with advancing age. Age was strongly inversely correlated with the amplitudes of both sensory and motor responses, accounting for 7--16% of the variance. Regression equations using both height and age improved this correlation, accounting for 7--22% of the variance. Therefore, both height and age must be taken into consideration when normal values are developed.

Orally administered atropine enhances motor cortex excitability: a transcranial magnetic stimulation study in human subjects

Oral application of atropine was used to test if a modulation of cholinergic neurotransmission changed motor excitability. Healthy volunteers received either 1 or 2 mg atropine. Paired transcranial magnetic stimulation was used to study intracortical inhibition and intracortical facilitation before, 1 h and 24 h after ingestion of atropine. In addition, the silent period, motor threshold, F wave and motor response amplitudes were measured. The 1 mg dose of atropine induced a loss of intracortical inhibition, the 2 mg dose produced an intracortical disinhibition and enhanced intracortical facilitation. These changes returned to baseline after 24 h. Other electrophysiological parameters remained unchanged. Thus, an antagonist of pre- and postsynaptic muscarinic receptors increased excitability in the human motor cortex in a dose-dependent manner, indicating an influence of the cholinergic system on motor cortex excitation.

Central conduction time of magnetic brain stimulation in attention-deficit hyperactivity disorder.

Twenty-seven children and adolescents aged 4 to 18 years, fulfilling the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria for attention-deficit hyperactivity disorder, were included in this study. The diagnosis was determined by a pediatric neurologist and a psychologist examined all 27 subjects with tests that included the Wechsler Intelligence Scale for Children-Revised (WISC-R) and reading, writing, handedness, personality, and anxiety scores. Subjects with histories of epilepsy, head injury, drug abuse, or psychotic disorders were excluded. Culturally based causes or emotional disorders were also excluded. Transcranial magnetic stimulation was performed on all subjects, with recording of the motor evoked potential at the biceps brachii. Central motor conduction time was calculated by cervical root stimulation. Due to shape variability, the amplitude of the motor responses was not measured in the study. The mean value of central conduction time in the subjects was very significantly increased (P < .001) compared to that in a group of normal controls, case-matched for IQ, age, and sex. A central motor conduction time greater than 12 ms indicates abnormality. A second finding in the subjects was the significant difference of central conduction time on the side-to-side stimulation (P = .03). These findings are correlated with delay in the maturation of the corticomotoneuronal system and might provide neurophysiologic data for diagnosis.

Comparison of Heteronymous Monosynaptic Ia Facilitation in Young and Elderly Subjects in Supine and Standing Positions

Background The control of posture and balance is a primary concern among the elderly. Postural instability has been identified as a contributor to the greater incidence of falling among this segment of the population. One important neuromuscular mechanism identified as important in the control of posture and balance is the segmental reflex system. The purpose of this study was to examine the role of presynaptic inhibition in modulating the reflex system in young and elderly subjects.Methods To estimate the influence of body position on presynaptic inhibition to the soleus motor pool between young and elderly subjects, 11 young (mean age = 23.9 yrs.) and 9 elderly (mean age = 72.1 yrs.) subjects were examined in two different body positions: supine and standing. This study utilized the heteronymous facilitation protocol, as described by Hultborn et at. (1987). to estimate presynaptic inhibition of the la afferent pathway onto the soleus o-motoneuron pool. Maximal soleus H-reflex (H-max) and motor response (M-max) amplitudes were determined prior to testing at each condition, and the H-max/M-max ratio at each body position was determined. To estimate presynaptic inhibition at each body position, subjects received 24 test soleus H-reflex stimuli (~15% M-max), and 24 soleus H-reflexes conditioned by stimulation of the ipsilateral femoral nerve.Results Results demonstrated a significant decrease in H-max/M-max ratio from supine (66.1%) to standing (56.8%) for the young subjects, whereas the elderly subjects demonstrated no changes in the H-max/M-max ratio between body positions (39.8% supine; 39.8% standing). The conditioning stimulus produced a significant change in the test reflex for the young subjects during supine testing (51.1% increase) but not standing (3.4% increase). The elderly subjects demonstrated no significant changes in the test reflex produced by the heteronymous conditioning at either condition (17.6% increase supine; 4.9% increase standing).Conclusions These results demonstrate differential effects of both H-reflex modulation and heteronymous conditioning for elderly subjects when compared with young adults. These differences may be an adaptive phenomenon of the aging neuromuscular system, exemplified by a decreased ability to modulate the reflex system in the elderly group.