Entrainment to extinction of physiological tremor by spindle afferent input

Abstract

In this study the systematic modulation of wrist flexor muscle activity by imposed joint movement was examined. Ten subjects maintained a constant contraction level (25% of maximum; trial duration: 20 s) in flexor carpi radialis while their wrists were perturbed with 50 different quasi-sinusoidal signals (frequency range: 0.5 -9.5 Hz; amplitude: 0.3° -4.2°). Frequency spectra of wrist position and the rectified and filtered electromyogram (EMG) were determined. The muscle activity was only weakly entrained to imposed movements of small amplitude and low frequency, as shown by a small peak in the EMG spectrum at the frequency of movement, while the most prominent peak in the spectrum was between 9 -15 Hz, corresponding to the frequency range of physiological tremor. The entrainment of muscle activity increased markedly as the amplitude and frequency of the imposed movement increased, to the point of saturation of modulation and harmonic peaks in the spectrum. In parallel with this increase in entrainment, the 9 -15 Hz tremor peak was progressively extinguished. The results are consistent with a coupled oscillator model in which the central oscillatory source(s) of tremor became fully entrained to the imposed movement at the highest amplitudes and frequencies. Such coupling depends on communication between the external forcing oscillator and the central oscillator(s), the Ia afferent signal from the imposed movement being the most likely candidate to provide the entraining signal for the central oscillator(s).

Speech motor control in fluent and dysfluent speech production of an individual with apraxia of speech and Broca's aphasia

“…However, people with AOS may be at the high end of vulnerability in terms of their individual amplitude/peak velocity thresholds or in the way afferent information is entrained by the neural oscillator system (cf. Cathers, O'Dwyer, & Neilson, 2006). Possible contributions may include a limited ability to adequately scale individual movements in the context of gestural blending or co-articulation, a crucial process in the expression of linguistic contrasts according to LGM (Browman & Goldstein, 1991;Lö fqvist, 1999).…”

Periodontal-Masseteric Reflexes Decrease with Tooth Pre-load

“…Given the unique nature of the stimulation protocol used in this study, we can be sure that the negative correlation seen here between the stimulus interval and the degree of coupling that occurred between the stimulus and the masseteric EMG was not due to the rate sensitivity of the periodontal mechanoreceptors. Rather, we ascribe this effect to a carrier-dependence phenomenon, whereby the entrainment of motoneurones to a periodic signal became strongest when the input signal approached the mean motoneuronal firing rate (Cathers et al, 2006). Applying this theory to the masticatory muscles, which have generally higher firing rates than those seen in limb muscles, one would expect to see a linear increase in entrainment up to and above 20 Hz (van Boxtel and Schomaker, 1983), as we observed in this study.…”

Tremor: From Pathogenesis to Treatment

“…The amplitude is small and is barely seen with the naked eye (Cathers et al, 2006). Physiological tremor's frequency is reduced by addition of inertia (Elble, 2003; see Figure 1.1a) and is age-independent .…”

“…Moreover, in the case of essential tremor, inadequate function of the cerebellum (whose function might be to compensate by adjusting timing/gain of the feedback loop to minimise tremor) occurs. Other studies have demonstrated the systematic interaction between imposed joint movement and wrist flexor muscle activity, showing that the imposed movement of large amplitude takes progressive control over the afferent input and markedly increases the entrainment of the muscle activity via the stretch reflex (Cathers et al, 2006).…”