Repetitive doublets in human flexor carpi radialis muscle.

Bawa, Parveen; Calancie, Blair

doi:10.1113/jphysiol.1983.sp014707

Cited by 133 publications

(132 citation statements)

References 22 publications

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“…In contrast, 45 % (9 of 20) of the F cells showed doublet firing. Doublet discharge in motoneurons has been reported in a variety of experimental preparations including (1) healthy humans during weak voluntary contractions (Bawa & Calancie, 1983), (2) reflexive motor unit recruitment in decerebrate cats (Cordo & Rymer, 1982), (3) controlled locomotion in decerebrate cats (Zajac & Young, 1980), (4) intracellular current injection in cat motoneurons (Calvin, 1975), and (5) various pathological conditions in humans (Koenig & Stoehr, 1986). Interestingly, doublets were not observed in the intracellular study of Kernell & Monster (D. Kernell, personal communication).…”

Section: Discussionmentioning

confidence: 99%

Adaptation of cat motoneurons to sustained and intermittent extracellular activation.

Spielmann

Laouris

Nordstrom

et al. 1993

The Journal of Physiology

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SUMMARY1. The main purpose of this study was to quantify the adaptation of spinal motoneurons to sustained and intermittent activation, using an extracellular route of stimulating current application to single test cells, in contrast to an intracellular route, as has been used previously. In addition, associations were tested between firing rate properties of the tested cells and other type (size)-related properties of these cells and their motor units.2. Motoneurons supplying the medial gastrocnemius muscle of the deeply anaesthetized cat were stimulated for 240 s with microelectrodes which passed sustained extracellular current at 1-25 times the threshold for repetitive firing. Many cells were also tested following a rest period with intermittent 1 s current pulses (duration 600 ms) at the same relative stimulus strength. Cell discharge was assessed from the EMG of the motor unit innervated by the test neuron. The motoneurons and their motor units were assigned to four categories (i.e. types FF, FR, S and F; where F = FF + FR) based on conventional criteria. In all, twenty F (16 FF, 4 FR) and fourteen S cells were studied with sustained stimulation. Thirty of these cells (17 F, 13 S) 4. All cells exhibited a delay from the onset of current to the first spike, followed by a brief accelerating discharge that was followed by a slower drop in firing rate. Some cells (21 of 34 with sustained activation; 20 of 32 with intermittent) exhibited doublet discharges (interspike intervals < 10 ms) that were intermingled with the more predominant singlet discharges. Doublets were more common in the S cell type.5. With sustained activation, the mean delay from the onset of current to the first spike was 2-6 + 1 1 s for F cells, and 3-2 + 1-9 s for S cells. The time required to reach peak frequency of singlet discharge following repetitive firing onset was significantly shorter for F than S cells (7-0 + 5 0 vs. 14-3 + 13-6 s) and the peak singlet frequencies also differed significantly (F, 28-0 + 7-7 Hz vs. S, 15-6 + 2-5 Hz). Subsequently, the mean magnitude of firing rate reduction from the peak to 24 s later was significantly greater for F cells than that for S cells (16-2 + 6 Hz vs. 5X8 + 3 Hz). These gradual reductions in firing frequency for both F and S cells during the course of their sustained stimulation were qualitatively similar to the late adaptation observed in previous studies that had employed intracellular stimulation.6. The time course of firing frequency for each unit with sustained activation was fitted with a double-exponential equation: the first time constant (T1) for the initial increase in frequency was relatively short (F, 2X5 + 2-1 s vs. S, 3-7 + 4-1 s). The second time constant (r2) was significantly shorter for F than S cells (130-7 + 98-4 s vs. 750 0 + 402-4 s). It is argued that the r2 values provided a quantitative description of the type of adaptation termed 'late' in previous studies.7. The responses to intermittent stimulation were qualitatively similar to those seen with sustained activat...

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Section: Discussionmentioning

confidence: 99%

Adaptation of cat motoneurons to sustained and intermittent extracellular activation.

Spielmann

Laouris

Nordstrom

et al. 1993

The Journal of Physiology

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“…Collision experiments suggest that facilitation causes some motor units to discharge twice or more with an interval of about 4 ms. Bawa & Calancie (1983) have shown that forearm flexor motor units can discharge as doublets with interspike intervals within this range. Multiple firing of motor units has also been shown to arise from single electrical brain shocks in humans (Day et al 1986b).…”

Section: Discu-ssionmentioning

confidence: 99%

Responses in small hand muscles from magnetic stimulation of the human brain.

Heß

Mills

Murray

1987

The Journal of Physiology

703

285

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SUMMARY1. The magnetic field generated by a brief current in a 9 cm diameter flat circular coil varies rapidly with time and when applied over the human scalp it is capable of exciting motor structures subserving the small hand muscles. With a peak magnetic field at the centre of the coil of 09-1-6 Tesla, single scalp stimuli produced twitches in the right abductor digiti minimi (a.d.m.), first dorsal interosseous (f.d.i.) and adductor pollicis muscles. Compound muscle action potentials (c.m.a.p.s) and single motor units from these muscles were recorded.2. The twitch force and corresponding c.m.a.p. were greatly enhanced by voluntary background contraction of the muscle and depended on the direction and intensity of the magnetic field. Response amplitude was maximal with the stimulating coil centred near the vertex but precise coil position was not critical.3. When the orthodromic volley set up in the peripheral nerve by magnetic stimulation of the brain collided with a maximal antidromic volley set up by stimulation at the wrist, remaining electromyographic (e.m.g.) activity gave evidence of multiple firing of some spinal motoneurones, provided that the muscle exerted a slight voluntary background contraction and the stimulus intensity was above threshold for relaxed muscle.4. When the muscle changed from total relaxation to a slightly contracted state the onset latency of the c.m.a.p. was shortened by about 3 ms without further change when the background contraction increased. In slightly contracted muscle, c.m.a.p. onset latency was little affected over a wide range of stimulus intensities and was unaffected by the position of the stimulating coil within an area of 6 x 6 cm over the vertex. 7. It is likely that the enhancement of responses by voluntary background contraction is caused by additional recruitment of higher-threshold motor units in the motoneurone pool and by multiple firing of some motor units.8. There may be two mechanisms of enhancement of responses to cortical stimulation, one related to a rise in excitability of homologous spinal motoneurone pools on the two sides, and a second operating at a higher level when the subject focuses his attention on the motor performance of a particular hand. The latter mechanism can be seen more easily with magnetic than with electrical brain stimulation, probably because the latter in part bypasses intracortical neuronal elements.

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“…However, motor units sometimes discharge doublets with short intervals followed by longer-than-average intervals, and successive intervals may be correlated negatively (Andreassen and Rosenfalck 1980). Under certain conditions, this alternation of short and long intervals may be accentuated (Bawa and Calancie 1983;Elble and Randall 1976). Andreassen and Rosenfalck (1980) adduced three possible mechanisms for such patterns: summation of motoneuronal afterhyperpolarization, recurrent inhibition and proprioceptive feedback.…”

Section: Physiological Significancementioning

confidence: 99%

Time constants of facilitation and depression in Renshaw cell responses to random stimulation of motor axons

et al. 1988

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Summary. In 9 adult anaesthetized cats, 22 lumbosacral Renshaw cells recorded with NaCl-filled micropipettes were activated by random stimulation of ventral roots or peripheral nerves. The stimulus patterns had mean rates of 9.5-13 or 20-23 or 45 pulses per second and were pseudo-Poisson; short intervals below ca. 5 ms (except in two cases) were excluded. The Renshaw cell responses were evaluated by two kinds of peristimulus-time histograms (PSTHs). "Conventional" PSTHs were calculated by averaging the Renshaw cell discharge with respect to all the stimuli in a train. These PSTHs showed an early excitatory response which was often followed by a longer-lasting slight reduction of the discharge probability. These two response components were positively correlated. "Conditional" PSTHs were determined by averaging the Renshaw cell discharge with respect to the second ("test") stimulus in pairs of stimuli which were separated by varied intervals, 6. The direct effect of the first "conditional" response was subtracted from the excitation following the second ("test") stimulus so as to isolate the effect caused by the second stimulus per se. After such a correction, the effect of the first "conditioning" stimulus showed pure depression, pure facilitation or mixed facilitation/depression. Analysis of such conditioning curves yielded two time constants of facilitation (ranges: ca. 435 ms and 93-102 ms) and two of depression (ranges: ca. 7-25 ms and 50-161 ms). It is concluded that these time constants are compatible with processes of short-term synaptic plasticity known from other synapses. Other processes such as afterhyperpolarization and mutual inhibition probably are of less importance.

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Repetitive doublets in human flexor carpi radialis muscle.

Cited by 133 publications

References 22 publications

Adaptation of cat motoneurons to sustained and intermittent extracellular activation.

Adaptation of cat motoneurons to sustained and intermittent extracellular activation.

Responses in small hand muscles from magnetic stimulation of the human brain.

Time constants of facilitation and depression in Renshaw cell responses to random stimulation of motor axons

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