Early facilitation at corticomotoneuronal synapses
TL;DR: Corticomotoneuronal EPSPs have been generated in lumbar motoneurones of the monkey by single and paired corticospinal volleys and the facilitation of the second of a pair of EPSPs with respect to the size of the first has been measured.
Abstract: 1. Corticomotoneuronal EPSPs have been generated in lumbar motoneurones of the monkey by single and paired corticospinal volleys. The facilitation of the second of a pair of EPSPs with respect to the size of the first has been measured.
2. The relationship between the degree of facilitation of the second response and the interval between the two volleys has been studied. Average facilitation of minimal EPSPs was found to be maximal about 2 msec after the arrival of the corticospinal volley and to decay roughly exponentially thereafter with a time constant of about 10 msec.
3. The degree of facilitation varied from one minimal corticomotoneuronal EPSP to another but this facilitation was not statistically correlated with the time course of the individual EPSPs.
4. Significant facilitation (0·4) was still present 10 msec after a corticospinal volley so that this phenomenon could play a part in the initiation of motoneuronal discharge by corticospinal activity at natural frequencies of the order of 100 impulses/sec.
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TL;DR: Evidence for "central" fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it.
Abstract: Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal cha...
3,200 citations
TL;DR: The sections in this article are: Methodological Considerations, General Summary and Epilogue, Ascending Pathways that Monitor Segmental Interneuronal Activity, and Evidence That Ascending FRA Pathways Monitor Activity in interneurons of Reflex Pathways.
Abstract: The sections in this article are:
1
Methodological Considerations
1.1
Selective Stimulation of Primary Afferents
1.2
Stimulation of Central Motor Systems
1.3
Methods for Investigation of Convergence at Interneuronal Level
2
Spinal Neuronal Circuits Used in Common by Segmental Afferents and Supraspinal Motor Centers
2.1
Recurrent Inhibition
2.2
Pathways From Ia-Afferents and Their Control by γ-Motoneurons
2.3
Reflex Pathways From Group Ib Tendon Organ Afferents
2.4
Reflex Pathways From Cutaneous and Joint Afferents and From Groups II and III Muscle Afferents
2.5
Propriospinal Neurons
2.6
Presynaptic Inhibition of Transmission From Primary Afferents
3
Reticulospinal Inhibition of Segmental Reflex Transmission
3.1
Dorsal Reticulospinal System
3.2
Ventral Reticulospinal Pathways
3.3
Monoaminergic Reticulospinal Pathways
3.4
Decerebrate Preparation
4
Direct Projections of Descending Pathways to α-Motoneurons
5
Ascending Pathways that Monitor Segmental Interneuronal Activity
5.1
Evidence That Ascending FRA Pathways Monitor Activity in Interneurons of Reflex Pathways
5.2
Information Via Ascending Collaterals of Interneurons
5.3
Ventral Flexor Reflex Tracts
5.4
Ventral Spinocerebellar Tract
6
General Summary and Epilogue
6.1
General Summary
6.2
Epilogue
662 citations
TL;DR: It is concluded that oscillations in the range 20–30 Hz are present in monkey motor cortex, are coherent between spatially separated cortical sites, and encompass the pyramidal tract output neurones.
Abstract: 1. Recordings were made of local field potential (slow waves) and pyramidal tract neurone (PTN) discharge from pairs of sites separated by a horizontal distance of up to 1.5 mm in the primary motor cortex of two conscious macaque monkeys performing a precision grip task. 2. In both monkeys, the slow wave recordings showed bursts of oscillations in the 20-30 Hz range. Spectral analysis revealed that the oscillations were coherent between the two simultaneously recorded cortical sites. In the monkey from which most data were recorded, the mean frequency of peak coherence was 23.4 Hz. 3. Coherence in this frequency range was also seen between cortical slow wave recordings and rectified EMG of hand and forearm muscles active during the task, and between pairs of rectified EMGs. 4. The dynamics of the coherence were investigated by analysing short, quasi-stationary data segments aligned relative to task performance. This revealed that the 20-30 Hz coherent oscillations were present mainly during the hold phase of the precision grip task. 5. The spikes of identified PTNs were used to compile spike-triggered averages of the slow wave recordings. Oscillations were seen in 11/17 averages of the slow wave recorded on the same electrode as the triggering spike, and 11/17 averages of the slow wave recorded on the distant electrode. The mean period of these oscillations was 45.8 ms. 6. It is concluded that oscillations in the range 20-30 Hz are present in monkey motor cortex, are coherent between spatially separated cortical sites, and encompass the pyramidal tract output neurones. They are discernable in the EMG of active muscles, and show a consistent task-dependent modulation.
641 citations
Cites background from "Early facilitation at corticomotone..."
...Unsurprisingly, short intervals gave a large postspike facilitation (PSF), probably due to summation and facilitation at the CM synapse (Porter, 1970)....
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TL;DR: The hypothesis that the central nervous system generates movement as a shift of the limb's equilibrium posture has been corroborated experimentally in studies involving single- and multijoint motions and can now be investigated in the neurophysiological machinery of the spinal cord.
Abstract: The hypothesis that the central nervous system (CNS) generates movement as a shift of the limb's equilibrium posture has been corroborated experimentally in studies involving single- and multijoint motions. Posture may be controlled through the choice of muscle length-tension curve that set agonist-antagonist torque-angle curves determining an equilibrium position for the limb and the stiffness about the joints. Arm trajectories seem to be generated through a control signal defining a series of equilibrium postures. The equilibrium-point hypothesis drastically simplifies the requisite computations for multijoint movements and mechanical interactions with complex dynamic objects in the environment. Because the neuromuscular system is springlike, the instantaneous difference between the arm's actual position and the equilibrium position specified by the neural activity can generate the requisite torques, avoiding the complex "inverse dynamic" problem of computing the torques at the joints. The hypothesis provides a simple, unified description of posture and movement as well as contact control task performance, in which the limb must exert force stably and do work on objects in the environment. The latter is a surprisingly difficult problem, as robotic experience has shown. The prior evidence for the hypothesis came mainly from psychophysical and behavioral experiments. Our recent work has shown that microstimulation of the frog spinal cord's premotoneural network produces leg movements to various positions in the frog's motor space. The hypothesis can now be investigated in the neurophysiological machinery of the spinal cord.
499 citations
TL;DR: In this paper, the authors draw together two groups of experimental studies on the control of human movement through peripheral feedback and centrally generated signals of motor commands, concluding that subjects can perceive their motor commands under various conditions, but that this is inadequate for normal movement.
Abstract: This target article draws together two groups of experimental studies on the control of human movement through peripheral feedback and centrally generated signals of motor commands. First, during natural movement, feedback from muscle, joint, and cutaneous afferents changes; in human subjects these changes have reflex and kinesthetic consequences. Recent psychophysical and microneurographic evidence suggests that joint and even cutaneous afferents may have a proprioceptive role. Second, the role of centrally generated motor commands in the control of normal movements and movements following acute and chronic deafferentation is reviewed. There is increasing evidence that subjects can perceive their motor commands under various conditions, but that this is inadequate for normal movement; deficits in motor performance arise when the reliance on proprioceptive feedback is abolished either experimentally or because of pathology. During natural movement, the CNS appears to have access to functionally useful input from a range of peripheral receptors as well as from internally generated command signals. The unanswered questions that remain suggest a number of avenues for further research.
380 citations
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TL;DR: The hypothesis is put forward that a residue of the ‘active calcium’ which enters the terminal axon membrane during the nerve impulse is responsible for short‐term facilitation.
Abstract: 1. The hypothesis is put forward that a residue of the ;active calcium' which enters the terminal axon membrane during the nerve impulse is responsible for short-term facilitation.2. This suggestion has been tested on the myoneural junction by varying the local calcium concentration so that during the first of two nerve impulses [Ca](o) is either much lower than, or raised to a level approaching that, during the second impulse. Facilitation is much larger in the latter case, which is in accordance with the ;calcium hypothesis'.3. A short pulse of depolarization focally applied to the junction is followed by a brief period of very intense facilitation. This can be seen in the tetrodotoxin-treated preparation, e.g. by lengthening the depolarization from 1 to 2 msec which can cause a more than fifty-fold increase in transmitter release. This large ;early facilitation' (which presumably occurs also during the course of a normal action potential) is discussed in relation to the ;calcium hypothesis'.
1,336 citations
TL;DR: It was found that for many PTNs, responses to the conditioned stimulus preceded the first peripheral electromyographic correlates of the conditioned response (wrist extension) and showed that they were not consequent upon feedback resulting from the movement.
Abstract: in a series P of studies of the relation of discharge 01 pyramlda1 tract neurons (PTNs) to voluntary movement. The first of the previous studies (5) showed that PTN activity both at rest and during movement is related to axonal conduction velocity. PTNs with the highest axonal conduction velocities tend to be silent during motor quiescence and to show phasic activity in association with movement. PTNs with lower axonal conduction velocities are for the most part active even in the absence of movement; with movement they show both upward and downward modulation of their resting discharge frequency. A second study (6) was carried out to obtain information as to the point in the interval between stimulus and response at which PTN discharge takes place in association with a conditioned hand movement. It was found that for many PTNs, responses to the conditioned stimulus (the onset of a light) preceded the first peripheral electromyographic correlates of the conditioned response (wrist extension). The fact that these PTN responses preceded the electromyographic response showed that they were not consequent upon feedback resulting from the movement. 1
1,243 citations
TL;DR: A process and apparatus for the conversion of anilinothiazolino amino acid derivatives of peptides and proteins for use with conventional sequencers in the overall Edman degradation process.
Abstract: A process and apparatus for the conversion of anilinothiazolino amino acid derivatives of peptides and proteins for use with conventional sequencers in the overall Edman degradation process. The apparatus comprises a modular unit separate from the sequencer having an independently programmable control and flow actuating and directing means including a source of pressurized nitrogen, a conversion reagent container, a wash solvent container, a reaction vessel, and a plurality of interconnecting tubes and valves controlled so as to regulate the amounts and durations of all fluids entering and leaving said reaction vessel under gas pressure.
995 citations
TL;DR: An analysis of cortically evoked pyramidal tract discharges recorded from sites where such distortion is minimized or absent indicates that records from the “region of pyramid decussation” are contaminated with, and often dominated by, activity in extrapyramidal neurons.
Abstract: THE EFFECT of exciting motor cortical areas is usually studied by recording muscle contractions or observing limb movements. Such studies yield little information about the central excitatory events which ultimately funnel into the final common motor pathway. Adrian and Moruzzi (1) were the first to recognize the importance of recording activity in the pyramidal tract. Their results were significantly supplemented by Lloyd’s (21) analysis of the effects of pyramidal volleys on spinal cord neurons. The present studies stemmed from a project in which cortically induced pyramidal discharges were to be used to assay cortical inhibitory mechanisms. As an initial step (31), we recorded from the region of pyramidal decussation and confirmed that single units isolated at this site have many of the properties described by Adrian and Moruzzi. Surprisingly, however, essentially different responses were recorded from the bulbar pyramid or the lateral column of the cervical spinal cord (31, 32, 33)~-i.e., above and below pyramidal decussation. The data indicate that records from the “region of pyramidal decussation” are contaminated with, and often dominated by, activity in extrapyramidal neurons. This report presents an analysis of cortically evoked pyramidal tract discharges recorded from sites where such distortion is minimized or absent. The analysis and terminology reported here and previously (31, 32, 33) have recently been confirmed by Wall et al. (37) and by Bertrand (4).
675 citations
TL;DR: The present paper is concerned with the stage of neuromuscular transmission at which facilitation and depression occur and with the question whether 'quantal' changes of e.p. amplitude are involved, involving either the number or the size of the miniature units of which the end-plate response is composed.
Abstract: When a series of impulses arrive at the nerve-muscle junction, the end-plate potentials (e.p.p.) which they produce are not constant but vary in size, depending on the number and frequency of the stimuli. Two main types of phenomena have been observed: (a) a progressive increase of the e.p.p. (facilitation, post-tetanic potentiation) and (b) a phase of depression (Wedenski-inlilbition, junctional fatigue). The present paper is concerned with the stage of neuromuscular transmission at which facilitation and depression occur and with the question whether 'quantal' changes of e.p.p. amplitude are involved. It has been suggested that the progressive synaptic changes during repetitive stimulation are due to a variation in the output of acetylcholine (ACh) from the motor nerve endings rather than to post-synaptic events (e.g. Feng, 1941 b; Hutter, 1952; Eccles, 1953, p. 89 seq.). In view of the recent evidence indicating that ACh release occurs in discrete quanta, it is of interest to inquire whether a functional change of ACh output takes place at quantal or molecular level, involving either the number or the size of the miniature units of which the end-plate response is composed.
577 citations