The frequency content of common synaptic inputs to motoneurones studied during voluntary isometric contraction in man.

Abstract

SUMMARY1. The discharges of pairs of individual motor units were recorded from intrinsic hand muscles in man. Single motor unit recordings were obtained either when both members of the motor unit pair were within first dorsal interosseous muscle (IDI: lDI recordings) or where one motor unit was within IDI and the other in second dorsal interosseous muscle (1DI:2DI recordings). The pairs of motor unit spike trains were cross-correlated in the time domain and the results compared to those of coherence analysis performed on the same spike train data. Central peaks were present in the cross-intensity functions, indicating the presence of common synaptic input to the motoneurone pair. Coherence analysis of these data indicated significant association between motor unit firing in the frequency ranges 1-12 and 16-32 Hz.2. Analysis of sequential non-overlapping segments of data recorded from individual motor unit pairs, demonstrated that both the central cross-intensity peak and coherence in the frequency bands 1-12 and 16-32 Hz were consistent features throughout a long recording. In these sequential recordings, the size of the central cross-intensity peak and the maximal value of coherence in the frequency band 16-32 Hz covaried from segment to segment. Analysis of the entire population of motor unit pairs confirmed a positive relationship between the magnitude of peak coherence and the size of the central cross-intensity peak.3. Voluntary sinusoidal co-modulation of the firing rates of pairs of individual motor units recorded from within IDI was found to produce significant values of coherence corresponding to the frequency of the common modulation. However, firing rate co-modulation was not found to affect either the size of the central crossintensity peak or the maximum value of coherence in the frequency band 16-32 Hz.4. Pairs of single motor units were recorded from within IDI and biceps brachii muscles of healthy subjects. The number and size of the central cross-intensity peaks and coherence peaks detected were compared for the two muscles. The incidence and size of central cross-intensity peaks and the incidence and magnitude of 16-32 Hz coherence peaks were both found to be greater for IDI recordings when compared to biceps brachii recordings. MS 9252 S. F. FARMER AND OTHERS5. Single motor unit recordings were made from the intrinsic hand muscles of a patient with severe peripheral deafferentation. Time-and frequency-domain analysis of these recordings revealed cross-intensity peaks and frequency bands of coherence similar to those seen in healthy subjects.6. Cross-correlation and coherence analysis was performed between lDI: IDI motor unit pairs from the affected and unaffected hands of eleven stroke patients. In comparison to recordings from sixteen healthy subjects, recordings from the affected IDI of stroke patients showed a reduction in the incidence and size of central crossintensity peaks. The incidence and size of significant peaks in the coherence spectra were also reduced. The difference between the...

Usefulness of intermuscular coherence and cumulant analysis in the diagnosis of postural tremor

“…We chose cumulant density In some data sets, cumulant analysis did not reveal any significant correlation structure between EMG bursts. In addition, when data was contaminated by EMG cross-talk as identified by the combination of a sharp narrow central peak (<10 ms) in the cumulant, broadband coherence (>0.5 above 30 Hz) and flat phase (Farmer et al 1993;Hansen et al 2005), the related data sets were excluded from further analysis.…”

Beta oscillations in a large-scale sensorimotor cortical network: Directional influences revealed by Granger causality

“…Specifically, beta oscillations in monkeys appear in local field potential (LFP) and spiking activity during tactile exploratory forelimb movements (4,7,8), movement preparation (5,6,9), and steady-state isometric contractions (10). Beta oscillatory activity is often observed to be synchronized between different parts of sensorimotor cortex (4,5,7,(9)(10)(11), between motor cortical LFPs and descending pyramidal tract neuron discharge (10,12), between single motor units (13,14), and between motor cortical activity and muscle activity (1,4,10,12,15,16).…”

“…Specifically, beta oscillations in monkeys appear in local field potential (LFP) and spiking activity during tactile exploratory forelimb movements (4, 7, 8), movement preparation (5, 6, 9), and steady-state isometric contractions (10). Beta oscillatory activity is often observed to be synchronized between different parts of sensorimotor cortex (4,5,7,(9)(10)(11), between motor cortical LFPs and descending pyramidal tract neuron discharge (10, 12), between single motor units (13,14), and between motor cortical activity and muscle activity (1,4,10,12,15,16).Although the role of beta oscillations in the outflow of activity from motor cortex to muscles is relatively well characterized for certain types of behavior, the relation of beta oscillations in postcentral areas and motor cortex remains poorly understood. This article addresses the functional relations between beta oscillations in pre-and postcentral cortical areas in premovement motor maintenance behavior.…”

Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults

“…concentric contraction; eccentric contraction; electromyogram; first dorsal interosseus; frequency spectrum THE FORCE EXERTED BY A MUSCLE during a voluntary contraction is not constant, but rather it fluctuates about an average value (2,15,25,33,36). The neural mechanisms most responsible for the fluctuations in the force exerted by hand muscles appear to be the regularity with which motoneurons discharge action potentials and the common modulation of motor unit discharge in the agonist and antagonist muscles (7,10,13,16,41). Fluctuations in muscle force impose a significant constraint on the ability of the nervous system to control movement by influencing the capacity to exert a desired force and to achieve an intended trajectory (17,18,43).…”

“…The neural mechanisms most responsible for the fluctuations in the force exerted by hand muscles appear to be the regularity with which motoneurons discharge action potentials and the common modulation of motor unit discharge in the agonist and antagonist muscles (7,10,13,16,41). Fluctuations in muscle force impose a significant constraint on the ability of the nervous system to control movement by influencing the capacity to exert a desired force and to achieve an intended trajectory (17,18,43).…”