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PubMed1986

On the innervation of trigeminal mesencephalic primary afferent neurons by adenosine deaminase-containing projections from the hypothalamus in the rat.

The localization and sources of adenosine deaminase-containing structures in the mesencephalic nucleus of the trigeminal nerve of the rat was studied using indirect immunofluorescence or immunoperoxidase immunohistochemical staining techniques for adenosine deaminase in combination with retrograde fluorescent tracing or lesion methods. The majority of large mesencephalic neurons were engulfed by a dense adenosine deaminase-immunoreactive plexus. Immunostaining was often punctate surrounding neuronal profiles or sometimes had the appearance of varicose fibers coursing over the neuronal surface. Occasionally, immunostained axons were found travelling towards and contacting mesencephalic neurons. Mesencephalic neuronal somas surrounded by immunofluorescence staining for adenosine deaminase were simultaneously labelled with fast blue after injections of this dye into the temporalis or masseter muscles of mastication. Injections of fast blue into the mesencephalic nucleus resulted in fast blue labelling of adenosine deaminase-immunoreactive neurons in the tuberal, caudal and postmammillary caudal magnocellular nuclei of the hypothalamus. Ablation of these hypothalamic nuclei caused a near total depletion of adenosine deaminase-immunostained fibers in the mesencephalic nucleus including those associated with mesencephalic neurons. It is concluded that adenosine deaminase-containing neurons in the posterior hypothalamus innervate mesencephalic primary sensory neurons, which are known to convey proprioceptive input to trigeminal motor nuclei controlling jaw muscles. The possibility is considered that the hypothalamus, via a direct action on these sensory neurons, may exert automatic control over jaw movements related to aggressive attack, defensive or feeding behavior. In addition, it appears that mesencephalic neurons may provide an ideal model system for electrophysiological investigations of the neurotransmitter(s) utilized by adenosine deaminase-containing hypothalamic projections.

Adenosine Deaminase↗

PubMed1975

The proprioceptive activation of stretch tension in pretibial flexor muscles induced by stimulation of antagonistic muscle afferents.

1. The effect of tetanic stimulation of ipsilateral group I afferents from the GS muscle on a synchronous stretch of the flexor EDL/TA muscles has been investigated in precollicular decerebrate cats. 2. The stretch-induced tension of the EDL/TA muscles increases remarkably during simultaneous stimulation of the GS nerve with maximal intensities corresponding to 1.5 times the threshold for the group 1 afferents. This increas appears above all in the dynamic part of stretch. 3. Under our experimental conditions there is no activation fo flexor-alpha-motoneurones during tetanic stimulation of the GS afferents without muscle stretch, as measured by the resting tension of the EDL/TA muscles. 4. Desptie an increase in the stretch-induced tension during fusimotor stimulation of antagonistic group I afferents, a transmission loss in the excitation via the psi-loop to the flexor-alpha-motoneurones occurs. This could be demonstrated by the ratio: increase in the tension T /increase in the number of Ia spikes. This is explained by snychronous convergence of the discharges of Ia inhibitory interneurones to the flexor-alpha-motoneurones. 5. The system studied demonstrates an input-output relation of the stretch reflex during conditions in which both reciprocal inhibition and autogenetic excitation via the psi-loop occur. It appears however, that the reciprocal inhibition is partly overwhelmed by the autogenetic excitation which results from the increase in the Ia discharge rate during fusimotor reflex. 6. It is postulated that static rather than dynamic psi-moto-neurones are involved in the investigated reflex arc.

Action Potentials↗

PubMed1986

Central input to primary afferent neurons in crayfish, Pacifastacus leniusculus, is correlated with rhythmic motor output of thoracic ganglia.

A preparation is described in which the thoracic ganglia of the crayfish are isolated together with the thoracocoxal muscle receptor organ (TCMRO) of the fourth leg. This preparation allows intracellular analysis of both centrally generated and reflex activity in leg motor neurons (MNs). The isolated thoracic ganglia can spontaneously generate a rhythmic motor pattern resembling that used during forward walking (Fig. 4). This involves the reciprocal activity of promotor and remotor MNs, with levator MNs firing in phase with promotor bursts. Stretch of the TCMRO in quiescent preparations evokes a resistance reflex in promotor MNs (Fig. 6). In more active preparations the response is variable and often becomes an assistance reflex, with excitation of remotor MNs on stretch (Fig. 7). When rhythmic motor patterns occur, the neuropilar processes of the S and T fibers receive central inputs that are strongly correlated with the oscillatory drive to the MNs and probably have the same origin (Figs. 8 and 9). Central inputs to the S and T fibers occur in opposite phases within a cycle of rhythmic motor output. The S fiber is depolarized in phase with promotor MNs and the T fiber in phase with remotor activity. The input to the T fiber is shown to be a chemical synaptic drive that has a reversal potential approximately 14 mV more depolarized than the fiber's resting membrane potential. This input substantially modulates the amplitude and waveform of passively propagated receptor potentials generated by TCMRO stretch (Fig. 11). It is argued that the central inputs to the TCMRO afferents will modulate proprioceptive feedback resulting from voluntary movements.

Afferent Pathways↗

PubMed1990

[Vestibular compensation. Review of the literature and clinical applications].

Vestibular compensation is an excellent model for the study of plasticity of the adult central nervous system. Therefore it has been the subject of several studies in humans and animals, which will be briefly summed up by the authors. Lesions of the labyrinth or vestibular neurectomy are immediately followed of postural and oculomotor disorders, as well as by dynamic deficits of the various vestibular reflexes (vestibulo-ocular and vestibulonucal reflexes). While the former problems always recede in all species, the restoration of the dynamic properties of vestibular reflexes largely depends upon the species considered, in particular for the vestibulo-ocular reflex. However, this function seems to recover the gain and phase it had prior to the lesion in both humans and monkeys. What is the neuronal substrate of these various deficits? Electrophysiological studies have demonstrated at the acute stage a symmetrical activity between the two vestibular nuclei: on the side of the lesion, the nucleus becomes inactive, while the resting discharge of the contralateral vestibular neurons is increased. Following compensation, symmetric activity is restored between both nuclei due to the regeneration of a new basic discharge in the deafferented neurons. The matter of vestibular compensation can therefore be formulated as follows: which mechanisms enable a central neuron inactivated du to the suppression of most of its excitatory afferences to recover a normal spontaneous activity? Several hypotheses, either pre- or postsynaptic, are currently put forward. Presynaptic hypotheses consider the role of the various afferences of the vestibular nuclei, ie. visual, proprioceptive, commissural, cerebellar and other afferences. In fact, the vestibular nuclei are not merely relays between the labyrinthine receptors and the nuclei of the oculomotor nerves, but actually form real sensorimotor integration centers. Besides the afferences from the vestibular nerve, they receive several other sorts of information, including visual and spinal proprioceptive inputs. An increase in the activity of these afferences, a sprouting of their axon collaterals, may favor the return to a normal basic discharge of the central vestibular neurons. The postsynaptic hypotheses involve either a change in the intrinsic membrane properties of the central vestibular neurons following the lesion, or an increase in the number of receptors located on their surface. More specifically, denervation supersensitivity of the glutamatergic receptors has been put forward as the possible origin of vestibular compensation.

Afferent Pathways↗

PubMed2004

Changes in corticomotor excitability of hand muscles in relation to static shoulder positions.

We examined whether the recruitment properties of the corticospinal pathway to intrinsic hand muscles are influenced by variations of the shoulder joint angle. Abductor digiti minimi (ADM) motor evoked potentials (MEPs) in response to transcranial magnetic stimulation were examined during different static positions of the shoulder joint in the horizontal plane from 30 degrees adduction to 30 degrees abduction with respect to the neutral position at 0 degrees, while elbow and wrist joints were constrained statically at 90 degrees and 180 degrees respectively. We found that 30 degrees abduction of the shoulder significantly depressed MEP size and prolonged MEP latency in comparison with 30 degrees shoulder adduction. The neutral shoulder angle position (at 0 degrees ) significantly reduced MEP size but had no effect on MEP latency in comparison with 30 degrees shoulder abduction. The input-output relationship between MEP size and stimulus intensity was sigmoidal. The plateau value and maximum slope were significantly lower at 30 degrees abduction than at 30 degrees adduction of the shoulder. However, the threshold value did not differ significantly between the two positions. To differentiate excitability changes at cortical versus subcortical sites, intracortical inhibition (ICI) and intracortical facilitation (ICF) were assessed using a paired-magnetic pulse paradigm. A significant decrease in ICF was observed after changing shoulder position from 30 degrees adduction to 30 degrees abduction. In contrast, no variation in the amount of ICI occurred in relation to the same changes in shoulder position. ADM F-waves elicited by electrical stimulation of the ulnar nerve at the wrist were significantly decreased at 30 degrees shoulder abduction in comparison with 30 degrees adduction. A similar pattern was observed in one subject in whom the H-reflex could be exceptionally elicited in ADM. We conclude that shoulder position influences the recruitment efficiency (gain) of the corticospinal volleys to motoneurons of intrinsic hand muscles. It is proposed that activity of peripheral receptors signalling static shoulder position influences corticomotor excitability of hand muscles both at the cortical and at the spinal level. This modulation may be functionally relevant when reaching to grasp objects.

Action Potentials↗

PubMed1993

Fusimotor discharge patterns during rhythmic movements.

Sensory information from muscle is a major factor in the control of posture and movement. The central nervous system can greatly vary this proprioceptive feedback via the fusimotor (gamma) system that innervates the muscle spindle, a length receptor. Despite 50 years of intensive research, the role of the fusimotor system still remains controversial. One of the major reasons for this state of affairs is, because of technical difficulties, the complete lack of direct recordings from classified gamma-motoneurones (that is, static or dynamic) in intact animals. However, such recordings have been achieved in reduced feline preparations during three types of rhythmic movement: respiration, jaw movements and locomotion. The recordings indicate that the patterns of discharge of static and dynamic fusimotor neurones can vary in different types of movement, or in different muscles during the same behaviour. Notwithstanding such variation, a generalization has emerged in which it is proposed that, for rhythmic movements, extrafusal muscle contraction is accompanied by coactivity in static and dynamic gamma-efferents. Such coactivity serves to optimize spindle afferent feedback for reflex contributions to muscle contraction.

Animals↗

PubMedDate not supplied

Trigeminal evoked potentials and sensory deficits in atypical facial pain--a comparison with results in trigeminal neuralgia.

Trigeminal evoked potentials (TEPs) and sensory deficits in eighty-three patients admitted for first surgical treatment of facial pain were retrospectively analysed. Thirty-seven patients suffered from trigeminal neuralgia (TN), 10 from symptomatic TN (sTN), and 36 from atypical facial pain (AFP). Eighteen percent of the TN patients reported sensory deficits on the pain side, but 35% had delayed ipsilateral N13 waves. Of the sTN patients, 60% had either sensory deficits or a pathological corneal reflex and 62.5% a pathological N13. Of the AFP patients, 61% complained of sensory deficits, but only 31% had a pathological N13. The percentage of pathological P19 waves was slightly lower (20%, 50%, and 11%, respectively), but showed a similar trend. Normal TEPs were found even in the presence of a sensory deficit (reported only in the AFP group). These findings may add weight to the hypothesis of underlying psychiatric disorders in AFP.

Blinking↗

PubMed2003

Effect of semicircular canal stimulation on the perception of the visual vertical.

UNLABELLED: The subjective visual vertical (SVV) is usually considered a measure of otolith function. Herewith we investigate the influence of semicircular canal (SCC) stimulation on the SVV by rotating normal subjects in yaw about an earth-vertical axis, with velocity steps of +/- 90 degrees /s, for 60 s. SVV was assessed by setting an illuminated line to perceived earth vertical in darkness, during a per- and postrotary period. Four head positions were tested: upright, 30 degrees backward (chin up) or forward, and approximately 40 degrees forward from upright. During head upright/backward conditions, a significant SVV tilt (P < 0.01) in the direction opposite to rotation was found that reversed during postrotary responses. The rotationally induced SVV tilt had a time constant of decay of approximately 30 s. Rotation with the head 30 degrees forward did not affect SVV, whereas the 40 degrees forward tilt caused a direction reversal of SVV responses compared with head upright/backward. Spearman correlation values (Rho) between individual SCC efficiencies in different head positions and mean SVV tilts were 0.79 for posterior, 0.34 for anterior, and - 0.80 for horizontal SCCs. Three-dimensional video-oculography showed that SVV and torsional eye position measurements were highly correlated (0.83) and in the direction opposite to the slow phase torsional vestibuloocular reflex. IN CONCLUSION: 1) during yaw axis rotation without reorientation of the head with respect to gravity, the SVV is influenced by SCC stimulation; 2) this effect is mediated by the vertical SCCs, particularly the posterior SCCs; 3) rotationally induced SVV changes are due to torsional ocular tilt; 4) SVV and ocular tilts occur in the "anticompensatory," fast phase direction of the torsional nystagmus; and 5) clinically, abnormal SVV tilts cannot be considered a specific indication of otolith system dysfunction.

Acceleration↗

PubMed1978

Activity of pre-entral neurones in conscious monkeys: effects of deafferentation and cerebellar ablation.

After limb deafferentation, there was no gross alteration in the initiation and performance of a sound-triggered ballistic movement. The pattern of neuronal discharge in the arm area of the motor cortex was not significantly modified. In the absence of cerebellum, the reaction time of motor cortex cells was about 150 msec longer than the reaction time observed in normal and deafferented animals. This was associated with an equal retardation in the onset of ENG changes in the limb muscles. This observation is compatible with the idea that the motor cortex is normally situated downstream to the cerebellum in the initiation of some movements. However, the motor cortex is necessary for the initiation and execution of simple sound-triggered movements since its removal results in a permanent inability to perform the task. Finally, in the absence of peripheral feedback, the pattern of motor output to the agonistic and antagonistic muscles was initiated normally and thus appeared to be preprogrammed centrally. The importance of the motor cortex as a "reflex center" in the control of slower movements is obviously not challenged by these observations since the motor task that we have used depends very little or not at all on sensory feedback (Stark, 1968). What these results indicate, however, is that the execution of some voluntary fast ballistic movements can be entirely preprogrammed independently of peripheral and cerebellar influences, and that the program, which is mainly concerned with generating velocity signals, appears to require the integrity of the motor cortex for its execution.

Afferent Pathways↗

PubMed2004

Group II spindle fibres and afferent control of stance. Clues from diabetic neuropathy.

OBJECTIVE: Since patients with large-fibre neuropathy do not show abnormal body sway during stance, the hypothesis was tested that postural control is not impaired until myelinated fibres of medium size are affected. METHODS: In 22 diabetic neuropathic patients and 13 normals, we recorded: (1) body sway area (SA), (2) stretch responses of soleus (Sol) and flexor digitorum brevis (FDB) to toe-up rotation of a platform, (3) Sol and FDB H reflex and FDB F wave, (4) conduction velocity (CV) of tibial, deep peroneal and sural nerve. In patients, detection thresholds for vibration, cooling (CDT), warming and heat-pain (HPDT) were assessed. RESULTS: Body SA was increased in patients with respect to normals. Toe-up rotation elicited short- (SLR) and medium-latency (MLR) responses in Sol and FDB in all normals. In patients, SLR was absent in FDB and reduced in Sol, and MLR was delayed in both muscles; the FDB H reflex was absent. The CV of tibial nerve group II afferent fibres, as estimated from the afferent time of FDB MLR, was reduced in patients. All sensory detection thresholds were increased. Stepwise multiple regression showed that increased SA was explained by increased latency of MLR, decreased CV of group II fibres and augmented CDT and HPDT. CONCLUSIONS: Unsteadiness in diabetic neuropathy is related to alterations in medium-size myelinated afferent fibres, possibly originating from spindle secondary terminations.

Aged↗

PubMed2003

Fos and FRA protein expression in rat precerebellar structures during the Neurolab Space Mission.

Changes in gene expression were examined in precerebellar structures during and after space flight. These structures included the inferior olive (IO), the source of climbing fibers, and the lateral reticular nucleus (LRt) and basilar pontine nuclei (PN), sources of mossy fibers. We examined two immediate early gene products with two different time courses of expression: Fos, which persists only for a few (6-8)h after activation and FRA expression, which lasts for longer periods of time, i.e. hours and/or days after activation. Gravity effects on Fos and FRA gene expression were evident in vestibular and visual areas of the IO, including the dorsomedial cell column, the beta subnucleus and the dorsal cap of Kooy of the medial nucleus (which projects to the flocculonodular lobe, i.e. to the vestibular area of the IO involved in the olivary control of the vestibulo-ocular reflex (VOR)). Gene expression also affected the subnuclei A, B, and C and the caudal part of the medial IO. These olivary regions do not receive vestibular afferents, but rather spinal afferents, and are particularly involved in the olivary control of the vestibulospinal reflex (VSR). Changes in Fos expression were also observed in the LRt and the PN. We suggest that sensory substitution, in which signals produced by a subject's own activity replace activity normally provided by macular stimulation, contributes to the recovery of microgravity-related postural and motor deficits. While no consistent increases in FRA expression occurred in vestibular IO regions 24h after launch, consistent increases in FRA expression occurred 24h after landing. We hypothesize that this asymmetrical pattern of gene expression resulted from (i). tonic microgravity experienced after launch counteracting the effects of increased phasic gravitational forces experienced during launch, and (ii). the tonic gravitational field experienced after landing potentiating the effects of increased phasic gravitational forces experienced during landing. The specificity of these results is demonstrated by an absence of direct gravity-related changes in Fos expression in other precerebellar structures such as the external cuneate nucleus, group X, and the dorsal column nuclei that transmit exteroceptive and proprioceptive signals to thalamic nuclei and somatosensory areas of the cerebral cortex. The gravity-related Fos and FRA expression changes in the IO and the LRt seen here are of interest in view of the important role their projections play in adaptive gain changes of the VOR and VSR during sustained visuo-vestibular and neck-vestibular stimulation.

Animals↗

PubMed2002

Vestibular information is required for dead reckoning in the rat.

Dead reckoning is an on-line form of spatial navigation used by an animal to identify its present location and return directly to a starting location, even after circuitous outward trips. At present, it is not known which of several self-movement cues (efferent copy from movement commands, proprioceptive information, sensory flow, or vestibular information) are used to compute homeward trajectories. To determine whether vestibular information is important for dead reckoning, the impact of chemical labyrinthectomy was evaluated in a test that demanded on-line computation of a homeward trajectory. Rats were habituated to leave a refuge that was visible from all locations on a circular table to forage for large food pellets, which they carried back to the refuge to eat. Two different probe trials were given: (1) the rats foraged from the same spatial location from a hidden refuge in the light and so were able to use visual cues to navigate; (2) the same procedure took place in the dark, constraining the animals to dead reckon. Although control rats carried food directly and rapidly back to the refuge on both probes, the rats with vestibular lesions were able to do so on the hidden refuge but not on the dark probe. The scores of vestibular reflex tests predicted the dead reckoning deficit. The vestibular animals were also impaired in learning a new piloting task. This is the first unambiguous demonstration that vestibular information is used in dead reckoning and also contributes to piloting.

Animals↗

PubMed2005

Cortico-motoneuronal output to intrinsic hand muscles is differentially influenced by static changes in shoulder positions.

We investigated whether shoulder position influenced the recruitment properties of the abductor digiti minimi muscle (ADM) and first dorsal interosseous muscle (FDI). ADM and FDI motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) were obtained in seven healthy volunteers at two different static positions of the shoulder joint (30 degrees adduction vs 30 degrees abduction) while the arm was passively supported at shoulder level (90 degrees in the horizontal plane) and the elbow joint was fixed at 90 degrees . ADM and FDI voluntary activity was also examined during (1) externally paced finger abductions at 2 Hz in the two different shoulder positions (EMG(ADM) and EMG(FDI) was back-averaged time-locked to the end of finger abduction) and (2) maximal voluntary abduction of the little finger and the index finger. Maximal EMG power and force were analysed in the two shoulder positions. H-reflexes from ADM and FDI were also obtained in two subjects. The ADM stimulus-response curve to TMS showed that the slope and plateau level were significantly reduced with the shoulder at 30 degrees abduction. In contrast, the FDI stimulus-response curve to TMS was not influenced by shoulder position. The back-averaged EMG(ADM) showed a significant decrease in peak amplitude and area with the shoulder at 30 degrees abduction, while no change in EMG(FDI) was observed under the same condition. Similarly, maximal EMG(ADM) and force exertion by the little finger were significantly reduced with the shoulder at 30 degrees abduction, while no such effect was observed for FDI. ADM H-reflex, but not FDI, was also decreased with shoulder abduction. These results indicate that the corticospinal pathway to ADM is less accessible to TMS and to voluntary command when the shoulder is placed at 30 degrees abduction. In contrast, activation of FDI, whether by TMS or by volition, is not influenced by shoulder position. This finding suggests that there are differences in the corticospinal innervation to ADM and FDI, possibly due to the different role of these muscles in hand function.

Adult↗

PubMed1993

Contribution of periodontal receptors and food qualities to masseter muscle inhibition in man.

Previous studies of human muscle inhibition during chewing have shown that many factors contribute to the incidence and intensity of this reflex but few studies have been in a physiological context. During the first crushing cycle of brittle foods ipsilateral masseter muscle EMG, mandibular movement and vibration were recorded simultaneously in four healthy dentate subjects. Experiments were repeated before and during anaesthesia of the cheek teeth on the chewing side. The results suggest that vibration seems to be the most important factor in muscle inhibition during food crushing; conversely periodontal sensation, mandibular closing movement and the preload by the muscle at the onset of food fracture play a minor role.

Adult↗

PubMed1989

Vibration-evoked reciprocal inhibition between human wrist muscles.

Reciprocal inhibition of the voluntarily contracting wrist extensor (extensor carpi radialis, ECR) evoked by proprioceptive afferent input from the flexor (flexor carpi radialis, FCR), was studied in healthy human subjects. Vibration of the FCR tendon was used to elicit Ia-dominated afferent discharge whilst inhibition of ECR was assessed as the reduction in asynchronous, on-going EMG. A small early phase of inhibition (I1) was evident in 25% of trials. The latency (ca. 25 ms) of this component suggested that it was mediated by an Ia oligosynaptic. possibly 'classical' disynaptic, inhibitory pathway. A later and apparently separate phase of reduced activity (I2, ca. 40 ms) was, however, far more consistently observed (96% of trials) and of greater magnitude. The I2 component was usually followed, some 20 ms later, by a phase of elevated activity (E1, 72% trials). Reductions in simultaneously recorded net extensor torque commenced at about 60 ms following the onset of flexor tendon vibration, i.e. some 20 ms after the main I2 EMG component. These mechanical responses must have almost exclusively resulted from reciprocal inhibition of extensor EMG since vibration of the relaxed FCR evoked minimal excitatory flexor activity. The reflex pattern, in any individual subject, was relatively unaffected by altering the duration of the vibration train between one and nineteen cycles (125 Hz). This suggests that the entire response complex resulted largely from the initial afferent volley. The sizes of both the I1 and I2 reductions in ECR activity increased with increasing voluntary extensor contraction so that their depths remained constant proportions of background EMG. Very similar results were obtained when reciprocal inhibition of FCR was produced by vibration of the belly of ECR. Thus, reciprocal inhibition between wrist muscles is mainly expressed as a rather stereotyped, short duration reduction in EMG whose depth is determined by the pre-existing level of motor activity. Some functional implications of this form of reflex behaviour are discussed.

Adult↗

PubMed1989

Peripheral and descending control of neurones mediating non-monosynaptic Ia excitation to motoneurones: a presumed propriospinal system in man.

Evidence for a non-monosynaptic Ia excitation of wrist flexor and quadriceps motoneurones (MNs) in man has been provided while using two independent methods: construction of post-stimulus time histograms (PSTHs) of voluntarily activated motor units and the spatial facilitation of the H-reflex. This non-monosynaptic Ia excitation has a long central latency (3-6 ms) and a very low threshold. Neurones mediating this effect seem to receive a strong descending excitation at the onset of voluntary movement and it is argued that they might mediate part of the descending command to MNs. In contrast, increasing the afferent input produces an inhibition of the transmission in this pathway. Several characteristics of the non-monosynaptic excitation and its depression bear resemblance to those of the C3-C4 propriospinal system in the cat, which is used as a model for the discussion of the present results.

Action Potentials↗

PubMed1987

Sural nerve stimulation and motor control of tibialis anterior muscle in spastic paresis.

In patients with spastic paraparesis, increased extensor tonus can be decreased by stimulation of flexor reflex afferents. This should improve dorsiflexion of the foot and reduce the sense of effort. We therefore examined ability to maintain stable firing of a single motor unit (SMU) in tibialis anterior muscle and force of dorsiflexion in 17 normal subjects and 9 with spastic paresis, during several minutes of tonic nonpainful stimulation (20 Hz, 0.1 msec) of the sural nerve at the ankle (SNS). Subjects were asked to maintain stable SMU firing first with, then without auditory feedback of the motor unit potential. SNS was then applied for several minutes. In normal subjects, the force of dorsiflexion increased 33 +/- 26% with SNS and 2.5% +/- 5% without SNS (p less than 0.0005). Most subjects noted increased resistance to dorsiflexion during SNS that resulted in greater innervation of tibialis anterior muscle. In six abnormal subjects, the force of dorsiflexion increased 30 +/- 30% with SNS, but no increase was recorded without SNS. In normal subjects and those with spastic paresis of the legs, SNS increased innervation of tibialis anterior muscle and awareness of greater effort required to maintain constant innervation. The altered proprioception may depend on facilitation of motor neurons.

Electric Stimulation↗

PubMed1992

[Postural control in the elderly].

In order to investigate postural control in the elderly, a stabilometric investigation including fast Fourier Transform (FFT) analysis was conducted in three different age groups. The oldest group was composed of 16 subjects who ranged in age from 75 to 86 years: another group consisted of eight 65 to 74 year olds; the control group was composed of 21 young students. The subject was instructed to stand and look for 30 seconds at a spot in a CRT 50 cm ahead of his eyes, and to control body sway as indicated by the gravitational spot in the CRT. The subject was then told to stand with eyes closed for 30 seconds. Next, a 100 Hz vibratory stimulation was applied to the bilateral Achilles tendon in each trial. The data was filtered with a 10 Hz high cut filter and digitized at 25 Hz, and subsequently analyzed by a microcomputer (PC9801 VM 2). Thus, statistical analysis was performed in terms of area, length, and total frequency spectra from 0.10 Hz to 10.0 Hz in both lateral and antero-posterior directions. Sixteen power spectra of 0.249 Hz step from 0.10 to 3.96 Hz were demonstrated in the CRT and were also compared with those of the young group. When standing naturally, significant increases in body sway were found in terms of area, length, and total frequency spectra in the most elderly group as compared with the other two groups. There was no significant change in Romberg ratio between the elderly and the young groups. However, FFT analysis confirmed the influence of visual cues. When vibration was applied, no increases in body sway with regard to these parameters were demonstrated in the elderly, whereas significant increases were found in the young control group. This was especially evident in the eyes-closed trials, as previously reported. There were few increased frequency ranges in either lateral or antero-posterior sway in the elderly. This might suggest that proprioceptive afferent information play a less important role in elderly than in young subjects. When the subject was requested to minimize his own sway by utilizing visual feedback, no difference was found in this parameter between the elderly and young groups. However, FFT analysis of the elderly group revealed an increase of the power spectra close to 1.0 Hz in both lateral and antero-posterior sway, whereas increases of approximately 1.0 and 2.0 Hz in the power spectra and a decrease in the power spectrum from 0.10 to 0.29 Hz were found in both directions in young subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗