Autogenic and nonautogenic sensorimotor actions in the control of multiarticulate hand movements

Summary The relationship between the size of an afferent volley and the size of the short-latency cerebral potential produced by the volley is not linear for purely cutaneous afferents, mixed cutaneous and muscle afferents or purely muscle afferents. The cerebral potential approaches a maximum when the responsible afferent input is 50% of maximum, while cerebral potentials of about half maximal size require an afferent volley of about one fifth of maximum. The relationship for sural (cutaneous) afferents rises less steeply. This saturation probably results from the convergence of the most rapidly conducting components in each afferent volley at sequential subcortical relay nuclei. The present data is compared with published data from animal experiments.     

Stimulation of the group I extensor afferents prolongs the stance phase in walking cats

Group I afferents in nerves innervating the lateral gastrocnemius-soleus (LG-Sol), plantaris (P1), and vastus lateralis/intermedius (VL/VI) muscles were stimulated during walking in decerebrate cats. The stimulus trains were triggered at a fixed delay following the onset of bursts in the medial gastrocnemius muscle. Stimulation of all three nerves with long stimulus trains (>600 ms) prolonged the extensor bursts and delayed the onset of flexor burst activity. LG-Sol nerve stimulation had the strongest effect; often delaying the onset of flexor burst activity until the stimulus train was ended. By contrast, flexor bursts were usually initiated before the end of the stimulus train to the P1 and VL/VI nerves. The minimum stimulus strength required to increase the cycle period was between 1.3×threshold and 1.6×threshold for all three nerves. Simultaneous stimulation of the P1 and VL/VI nerves produced a larger effect on the cycle period than stimulation of either nerve alone. The spatial summation of inputs from knee and ankle muscles suggests that the excitatory action of the group I afferents during the stance phase is distributed to all leg extensor muscles. Stimulation of the group I afferents in extensor nerves generally produced an increase in the amplitude of the heteronymous extensor EMG towards the end of the stance phase. This increase in amplitude occurred even though there were only weak monosynaptic connections between the stimulated afferents and the motoneurones that innervated these heteronymous muscles. This suggests that the excitation was produced via oligosynaptic projections onto the extensor motoneuronal pool. Stimulation with 300 ms trains during the early part of flexion resulted in abrupt termination of the swing phase and reinitiation of the stance phase of the step cycle. The swing phase resumed coincidently with the stimulus offset. Usually, stimulation of two extensor nerves at group I strengths was required to elicit this effect. We were unable to establish the relative contributions of input from the group 1a and group 1b afferents to prolonging the stance phase. However, we consider it likely that group Ib afferents contribute significantly, since their activation has been shown to prolong extensor burst activity in reduced spinal preparations. Thus, our results add support to the hypothesis that unloading of the hindlimb during late stance is a necessary condition for the initiation of the swing phase in walking animals.     

Reflex responses in active muscles elicited by stimulation of low-threshold afferents from the human foot.

1. Reflex responses were elicited in muscles that act at the ankle by electrical stimulation of low-threshold afferents from the foot in human subjects who were reclining supine. During steady voluntary contractions, stimulus trains (5 pulses at 300 Hz) were delivered at two intensities to the sural nerve (1.2-4.0 times sensory threshold) or to the posterior tibial nerve (1.1-3.0 times motor threshold for the intrinsic muscles of the foot). Electromyographic (EMG) recordings were made from tibialis anterior (TA), peroneus longus (PL), soleus (SOL), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles by the use of intramuscular wire electrodes. 2. As assessed by averages of rectified EMG, stimulation of the sural or posterior tibial nerves at nonpainful levels evoked a complex oscillation with onset latencies as early as 40 ms and lasting up to 200 ms in each muscle. The most common initial responses in TA were a decrease in EMG activity at an onset latency of 54 ms for sural stimuli, and an increase at an onset latency of 49 ms for posterior tibial stimuli. The response of PL to stimulation of the two nerves began with a strong facilitation of 44 ms (sural) and 49 ms (posterior tibial). With SOL, stimulation of both nerves produced early inhibition beginning at 45 and 50 ms, respectively. With both LG and MG, sural stimuli produced an early facilitation at 52-53 ms. However, posterior tibial stimuli produced different initial responses in these two muscles: facilitation in LG at 50 ms and inhibition in MG at 51 ms. 3. Perstimulus time histograms of the discharge of 61 single motor units revealed generally similar reflex responses as in multiunit EMG. However, different reflex components were not equally apparent in the responses of different single motor units: an individual motor unit could respond slightly differently with a change in stimulus intensity or background contraction level. The multiunit EMG record represents a global average that does not necessarily depict the precise pattern of all motor units contributing to the average. 4. When subjects stood erect without support and with eyes closed, reflex patterns were seen only in active muscles, and the patterns were similar to those in the reclining posture. 5. It is concluded that afferents from mechanoreceptors in the sole of the foot have multisynaptic reflex connections with the motoneuron pools innervating the muscles that act at the ankle. When the muscles are active in standing or walking, cutaneous feedback may play a role in modulating motoneuron output and thereby contribute to stabilization of stance and gait.     

Reflex pathways connect receptors in the human lower leg to the erector spinae muscles of the lower back

Reflex pathways connect all four limbs in humans. Presently, we tested the hypothesis that reflexes also link sensory receptors in the lower leg with muscles of the lower back (erector spinae; ES). Taps were applied to the right Achilles’ tendon and electromyographic activity was recorded from the right soleus and bilaterally from ES. Reflexes were compared between sitting and standing and between standing with the eyes open versus closed. Reflexes were evoked bilaterally in ES and consisted of an early latency excitation, a medium latency inhibition, and a longer latency excitation. During sitting but not standing, the early excitation was larger in the ES muscle ipsilateral to the stimulation (iES) than in the contralateral ES (cES). During standing but not sitting, the longer latency excitation in cES was larger than in iES. This response in cES was also larger during standing compared to sitting. Responses were not significantly different between the eyes open and eyes closed conditions. Taps applied to the lateral calcaneus (heel taps) evoked responses in ES that were not significantly different in amplitude or latency than those evoked by tendon taps, despite a 75–94% reduction in the amplitude of the soleus stretch reflex evoked by the heel taps. Electrical stimulation of the sural nerve, a purely cutaneous nerve at the ankle, evoked ES reflexes that were not significantly different in amplitude but had significantly longer latencies than those evoked by the tendon and heel taps. These results support the hypothesis that reflex pathways connect receptors in the lower leg with muscles of the lower back and show that that the amplitude of these reflexes is modulated by task. Responses evoked by stimulation of the sural nerve establish that reflex pathways connect the ES muscles with cutaneous receptors of the foot. In contrast, the large volley in muscle spindle afferents induced by the tendon taps compared to the heel taps did not alter the ES responses, suggesting that the reflex connection between triceps surae muscle spindles and the ES muscles may be relatively weak. These heteronymous reflexes may play a role in stabilizing the trunk for maintaining posture and balance.     

Afferent control of human stance and gait: evidence for blocking of group I afferents during gait

Summary The cerebral potentials (c.p.) evoked by electrical stimulation of the tibial nerve during stance and in the various phases of gait of normal subjects were compared with the c.p. and leg muscle e.m.g. responses evoked by perturbations of stance and gait. Over the whole step cycle of gait the c.p. evoked by an electrical stimulus were of smaller amplitude (3 V and 9 V, respectively) than that seen in the stance condition, and appeared with a longer latency (mean times to first positive peak: 63 and 43 ms, respectively). When the electrical stimulus was applied during stance after ischaemic blockade of group I afferents, the c.p. were similar to those evoked during gait. The c.p. evoked by perturbations were larger in amplitude than those produced by the electrical stimulus, but similar in latencies in both gait and stance (mean 26 V and 40 V; 65 ms and 42 ms, respectively) and configurations. The large gastrocnemius e.m.g. responses evoked by the stance and gait perturbations arose with a latency of 65 to 70 ms. Only in the stance condition was a smaller, shorter latency (40 ms) response seen. It is concluded that during gait the signals of group I afferents are blocked at both segmental and supraspinal levels which was tested by tibial nerve stimulation. It is suggested that the e.m.g. responses induced in the leg by gait perturbations are evoked by group II afferents and mediated via a spinal pathway. The c.p. evoked during gait most probably reflect the processing of this group II input by supraspinal motor centres for the coordination of widespread arm and trunk muscle activation, necessary to restablish body equilibrium.     

Task-dependent gating of somatosensory transmission in two different motor tasks in man: falling and writing

The cerebral potentials induced by an electrical stimulus (median nerve or finger) were recorded over the central region of the scalp and were analysed during falling onto the extended arms or during writing to investigate the influence of different motor tasks on the transmission of a synchronous afferent volley to the brain. During both falling (before landing) and writing, the first peaks (20-40 ms) were reduced. Later peaks (60-200 ms) were enhanced during writing but reduced during falling. A reduction of the first peak was also obtained after ischaemic blockade of group I afferents, suggesting that the cerebral transmission of group I afferents is inhibited during falling and writing. The subjects reported a corresponding reduction in the perception of the stimulus during falling. During writing, however, the large late waves indicate a task specific processing of the remaining afferent volley. Such a gating of sensory information to the brain is assumed to play a functional role in the respective motor tasks.     

The distribution of cutaneous receptors in the rabbit's hind limb and differential electrical stimulation of their axons

1. The receptive field properties and conduction velocities of single dorsal root axons, activated from the sural and cutaneous branches of the posterior tibial (medial plantar) nerves, were examined in anaesthetized rabbits.

2. The sural nerve sample included all types of units previously recorded from the saphenous nerve (Brown & Iggo, 1967). In particular it was shown that electrical stimulation of the sural nerve at strengths up to 1·3T produced a volley of impulses in a pure population of slowly adapting units (Type I units).

3. The medial plantar sample showed an absence of Type I slowly adapting units and Type T hair follicle units. Corresponding to this there were no touch corpuscles or tylotrich hairs in the skin of the hind foot and the fastest medial plantar axons conducted at 60-70 m/sec as opposed to 80-85 m/sec for the sural nerve. Stimulation of the medial plantar nerve at stimulus strengths close to threshold produced a volley of impulses in a nearly pure population of Type G hair follicle units.

     

Reflexes induced by nerve stimulation in walking cats with implanted cuff electrodes

Summary Neural cuffs, implanted around various hindlimb nerves (sural, common peroneal, posterior tibial), were used to deliver brief stimulus trains to unrestrained cats walking on a treadmill. The resulting perturbations of the step cycle were evaluated by analyzing the EMG bursts recorded from the ankle extensors and by high speed cinematography. It was found that relatively weak stimulation (1.4 to 2 X T) of the posterior tibial nerve was very effective in eliciting a prolongation of the flexion phase provided the stimuli were applied just prior to the expected onset of the ankle extensor EMG burst. This ipsilateral hyperflexion was correlated with a prolongation of the contralateral extension. The same stimuli applied during stance usually evoked a yielding of the stimulated leg and a prolongation of the ongoing contralateral stance. In addition to these flexor and extensor reflex effects, it was found that low threshold stimulation of the sural and common peroneal nerves resulted in a powerful reflex activation of the ankle extensors. In contrast, stimulation of the gastrocnemius-soleus nerve (a muscle nerve) produced no discernible behavioral effects, even for stimuli at 3 X T, indicating that the observed reflexes are probably mediated by cutaneous afferents. The results were largely confirmed in experiments using the same cuffs implanted in spontaneously walking premammillary cats.     

Responses to parallel fiber stimulation in the guinea pig dorsal cochlear nucleus in vitro

1. Parallel fibers of the guinea pig dorsal cochlear nucleus (DCN) were electrically stimulated at the pial surface of the nucleus in a brain-slice preparation. Extracellular field potentials produced by the parallel fibers and postsynaptic cells, and the response of single units were identified and characterized. Responses were compared with those reported for stimulation of parallel fibers in the cerebellum and to those seen with electrical stimulation of the auditory nerve. 2. Stimulation of the DCN parallel fibers generates a consistent set of extracellular field potentials. In layer 1 of the DCN, a short-latency triphasic wave (P1(1)-N1(1)-P2(1)) is followed by a slower negative wave (N2(1)). The onset phase of the N2(1) often exhibits a small positive notch (P2a1). In layer 2, an initial triphasic wave (P1(2)-N1(2)-P2(2)) is followed by a short-latency negative wave (N2(2)) and a slower positive wave (P3(2)). The N1(2) is approximately coincident with the N1(1), whereas the P3(2) is coincident with N2(1). The falling phase of the P3(2) is sometimes interrupted by a brief negative deflection (N3(2)). These field potentials are similar, but not identical to those reported for parallel fiber stimulation in the cerebellum in vivo (15). These responses differ substantially from those produced in the DCN by electrical stimulation of the auditory nerve (50). 3. Low-calcium solutions and pharmacologic manipulations were used to separate pre- and postsynaptic response components in the field potential records. When the slice is bathed in a low-calcium solution the P2a1, N2(1), N2(2), P3(2), and the brief late deflections are abolished. However, the P1(1)-N1(1)-P2(1) and P1(2)-N1(2)-P2(2) remain unaffected. A similar separation of pre- and postsynaptic components can be achieved with 100 microM adenosine or 0.5 mM kynurenic acid. It is concluded that the P1(1)-M1(1)-P2(1) wave is the compound action potential of the unmyelinated parallel fibers, whereas the longer-latency field potential components are generated postsynaptically. 4. The conduction velocity of the parallel fiber volley was measured to be 0.30 m/s at the pial surface, in a line approximately parallel to the strial axis of the nucleus. Mapping experiments reveal that the spread of the P1(1)-N1(1)-P2(1) is greatest along the strial axis, and more limited in the orthogonal direction. 5. Single units were recorded in layer 2. At a distance of 500-700 microns from the stimulating electrode, the latencies of single-unit discharges fall between 2.5 and 4 ms, at the time of the N2(2).(ABSTRACT TRUNCATED AT 400 WORDS)     

Phase-dependent reflex reversal in human leg muscles during walking

1. Reflex responses during walking were elicited in humans by stimulation of the tibial nerve at the ankle. The stimulus intensity was controlled by monitoring the M-wave from an intrinsic foot muscle. Responses were observed in the ipsilateral tibialis anterior (TA), soleus (SO), and rectus femoris (RF) muscles. The most reproducible responses were observed at a middle latency between 50 and 90 ms. The responses were most likely of cutaneous origin, because they closely resembled the responses to stimulation of a purely cutaneous nerve, the sural nerve. 2. A reversal in the direction of the middle latency response from excitation to inhibition was observed for the first time within single muscles during walking. Evidence for a reversal was seen in all three muscles examined and in all seven subjects. 3. The reflex reversal could not be elicited in standing. An inhibition whose amplitude varied in a linear fashion with stimulus intensity and background activation level was always observed at middle latency. The responses elicited during standing resembled those during the stance phase of walking. The two tasks shared some common movement goals and appeared to make use of similar reflex pathways.     

Fusimotor responses to volleys in joint and interosseous afferents in the cat''s hindlimb

The reflex effects of afferents running in the posterior articular nerve of the knee joint and the interosseous nerve were tested on fusimotor neurones in the lightly anaesthetised cat. Stimulation of these nerves activated fusimotor supplying various muscle groups in the hindlimb, in a pattern similar to that already described for cutaneous afferents of the sural nerve. Excitatory effects were found only if the stimulus strength exceeded twice threshold for the nerve volley. We were unable to obtain clear evidence that low threshold mechanoreceptors in joint or interosseous nerve contribute to the coordination of muscular activity via the fusimotor system.     

Somatosensory evoked potentials following proprioceptive stimulation of finger in man

Brisk passive flexion of the proximal interphalangeal joint of the middle finger, produced by using a newly devised instrument, elicited evoked potentials on the scalp. The present study carefully excluded the possible contribution of sensory modalities other than proprioception. The initial part of cortical response was a positive deflexion at the contralateral central area (P1 at 34.6 ms after the stimulus). This was followed by a midfrontal negative wave (N1 at 44.8 ms) and a clear positivity at the contralateral centroparietal area (P2 at 48.0 ms). The evoked responses persisted in spite of the abolition of cutaneous and joint afferents of the finger caused by ischemic anesthesia, but they were lost by ischemic anesthesia of the forearm. Thus, the cortical evoked responses obtained in this study most probably reflect muscle afferent inputs. The scalp distribution of P1 suggested that its cortical generator source was different from that of the N20-P20 components of evoked potentials to electrical median nerve stimulation. Brodmann areas 2 and 3a of human brain, which are known to receive deep receptor inputs, are the most plausible generator sites for the early components of the proprioception-related evoked responses. The amplitude of P2 was related to the velocity but not to the magnitude of movement. In conclusion, the present study established a method for recording the evoked responses to the brisk passive movement of the finger joint, which mainly reflect the dynamic aspects of proprioception mediated through muscle afferent.     

Inverse Effectiveness and Multisensory Interactions in Visual Event-Related Potentials with Audiovisual Speech

In recent years, it has become evident that neural responses previously considered to be unisensory can be modulated by sensory input from other modalities. In this regard, visual neural activity elicited to viewing a face is strongly influenced by concurrent incoming auditory information, particularly speech. Here, we applied an additive-factors paradigm aimed at quantifying the impact that auditory speech has on visual event-related potentials (ERPs) elicited to visual speech. These multisensory interactions were measured across parametrically varied stimulus salience, quantified in terms of signal to noise, to provide novel insights into the neural mechanisms of audiovisual speech perception. First, we measured a monotonic increase of the amplitude of the visual P1-N1-P2 ERP complex during a spoken-word recognition task with increases in stimulus salience. ERP component amplitudes varied directly with stimulus salience for visual, audiovisual, and summed unisensory recordings. Second, we measured changes in multisensory gain across salience levels. During audiovisual speech, the P1 and P1-N1 components exhibited less multisensory gain relative to the summed unisensory components with reduced salience, while N1-P2 amplitude exhibited greater multisensory gain as salience was reduced, consistent with the principle of inverse effectiveness. The amplitude interactions were correlated with behavioral measures of multisensory gain across salience levels as measured by response times, suggesting that change in multisensory gain associated with unisensory salience modulations reflects an increased efficiency of visual speech processing.     

65例颈椎型脊髓病体感诱发电位分析

目的研究颈椎型脊髓病皮质体感诱发电位（ＳＥＰ）变化。方法对６５例颈椎型脊髓病患者和２６例正常人进行正中神经和胫后神经刺激的ＳＥＰ对照研究，并对１０例患者作治疗前后对照观察。结果本组异常率为４５％，主要表现为各波替伏期和波间期（Ｎ２０—Ｐ２５，Ｐ２５—Ｎ３５，Ｐ４０—Ｎ４５）延长，且下肢的延长更加明显，部分患者出现波形分化不良。经保守治疗后６例正常，２例好转，且ＳＥＰ的好转先于临床的改善。结论ＳＥＰ对评判颈椎型脊髓病的脊髓传导功能具有重要的意义，且有助于临床预后的评价。     

Median nerve and posterior tibial nerve somatosensory evoked potentials in the non-affected hemisphere: a prospective one-year follow-up study in patients with supratentorial cerebral infarction

Somatosensory potentials in the non-affected hemisphere evoked by simulation of both the median nerve (median nerve SEPs) and the posterior tibial nerve (tibial nerve SEPs) were studied in 40 patients with supratentorial nonhaemorrhagic cerebral infarction three times during a one-year follow-up period. The EP-N20 interpeak latencies (IPLs) of the median nerve SEPs were on average longer in the patient group than in the control group (especially in patients with evidence of mass displacements in the cerebral computed tomography), whereas no significant differences were observed in the amplitudes of the median nerve SEPs. The P57-N75 amplitudes of the tibial nerve SEPs were on average lower in the patient group than in the control group. During the follow-up period the peak latencies and the P40-N75 IPLs of the tibial nerve SEPs increased and the amplitudes of the tibial nerve SEPs diminished.     

Electrophysiological correlates of short-latency afferent inhibition: a combined EEG and TMS study

Cutaneous stimulation produces short-latency afferent inhibition (SAI) of motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS). Since the demonstration of SAI is primarily based on the attenuation of MEPs, its cortical origin is not yet fully understood. In the present study we combined TMS with concurrent electroencephalography (EEG) in order to obtain direct cortical correlates of SAI. TMS-evoked EEG responses and MEPs were analysed with and without preceding electrical stimulation of the index finger cutaneous afferents in ten healthy volunteers. We show that the attenuation of MEPs by cutaneous stimulation has its counterpart in the attenuation of the N100 EEG response. Moreover, the attenuation of the cortical N100 component correlated positively with the strength of SAI, indicating that the transient changes in cortical excitability can be reflected in the amplitude dynamics of MEPs. We hypothesize that the hyperpolarization of the pyramidal cells due to SAI lowers the capacity of TMS to induce the inhibitory current needed to elicit N100, thus leading to its attenuation. We suggest that the observed interaction of two inhibitory processes, SAI and N100, provides further evidence for the cortical origin of SAI. R. Bikmullina and D. Kičić equally contributed to the study.     

Gating of sensation and evoked potentials following foot stimulation during human gait

To investigate how gait influences the perceived intensity of cutaneous input from the skin of the foot, the tibial or sural nerves were stimulated at the ankle during walking or running on a treadmill. As compared to standing, the detection threshold for these stimuli was raised by more than 30% during the locomotion tasks. During walking, there was a phase-dependent modulation in perceived intensity of suprathreshold stimuli (1.5, 2, or 2.5×PT). Stimuli given just prior to footfall were perceived as significantly above average (Wilcoxon signed-rank test). In contrast there was a significant phasic decrease in sensitivity for shocks delivered immediately after ipsi- and contralateral footfall. The amplitude of somatosensory evoked potentials (P50–N80 complex), simultaneously evoked from pulse trains to the sural nerve and recorded at scalp level, was, on average, 62% of the level during standing. During gait, the amplitude of this complex was significantly smaller just after footfall than the amplitude during late swing (MANOVA). It is suggested that the reduced sensation and the decreased evoked potentials after touchdown may be due to occlusion or masking by concomitant afferent input from the feet. On the other hand, the phasic increase in sensitivity at the end of swing is thought to result from a centrally generated facilitation of sensory transmission of signals in anticipation of foot-placing.     

Reflex activation of muscle spindles in human pretibial muscles during standing

1. Experiments were performed in standing subjects to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the human foot reflexly influence fusimotor neurons innervating pretibial flexor muscles. Recordings were made from 30 identified muscle-spindle afferents, four tendon-organ afferents, and one alpha-motor axon innervating the pretibial flexor muscles. The subjects stood without support or vision on a force platform while trains of electrical stimuli (5 stimuli, 300 Hz) were delivered at nonpainful intensities to the sural nerve or to the posterior tibial nerve at the ankle. 2. Seventeen of the 30 spindle endings had no background discharge, and none was activated by the sural or posterior tibial stimuli. Five silent afferents were given a background discharge by sustained pressure on the relevant tendon, but with two the discharge was dominated by a tremor rhythm obscuring any reflex response to the stimuli. Based on peristimulus time histograms (PSTHs), the sural stimuli then produced increases in discharge of two of the remaining three endings at latencies of 84 and 90 ms. These effects could not be explained by muscle stretch and are presumed to have been fusimotor mediated. 3. When the subjects stood freely without support or vision, 13 muscle-spindle endings had a background discharge, but with three endings tremor developed at the ankle and dominated the spindle discharge. Sural stimuli affected the discharge of five of nine endings unaffected by tremor. With three of these endings, there were changes in discharge that could be explained by muscle stretch.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in somatosensory evoked potentials and reflectory reactions of human hand muscles to nociceptive stimulation of index finger before and during ischemia

Somatosensory evoked potentials and reflectory reaction ofm. thenar to nociceptive electrical stimulation of the index finger before and during its ischemia were studied in healthy volunteers. The amplitude of early components of the somatosensory evoked potentials N23-P31 and N50-P120 correlated with stimulus intensity, while the amplitude of N140-P200 did not depend on both stimulus intensity and pain. The nociceptive RIII reflex recorded fromm. thenar was the most reliable index of pain caused by electrical stimulation of the finger. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 129, No. 3, pp. 265–268, March, 2000