Coding of pulsatile motor output by human muscle afferents during slow finger movements.

Abstract

1. Impulse activities of thirty‐eight muscle spindle and tendon organ afferents from the finger extensor muscles were recorded in the radial nerve of human subjects while the subjects performed voluntary flexion and extension finger movements at a single metacarpophalangeal joint. 2. The afferent firing was analysed in relation to the 8‐10 Hz discontinuities which previously have been shown to characterize these movements. Spike‐triggered averaging and frequency domain analyses demonstrated that all Ia muscle spindle afferents and a large proportion of group II spindle afferents responded in close association with local peaks in the joint acceleration. During muscle lengthening the impulses appeared during phases of rapid muscle stretch, whereas they appeared during the phase of minimal speed during muscle shortening. 3. The Golgi tendon organ (Ib) afferents displayed a reverse pattern of activity in relation to the discontinuities, i.e. the impulses tended to appear in the phase of minimal speed during lengthening movements and close to maximal shortening speed during shortening movements. Hence, their firing often coincided with the phasic increases of the parent muscle activity which account for the 8‐10 Hz discontinuities. 4. A close analysis of the time relations between spindle firing and the kinematics of the 8‐10 Hz discontinuities revealed that the population spindle response was too delayed and too dispersed to support the hypothesis that the discontinuities are accounted for by the stretch reflex. 5. If, as suggested in a previous paper, the 8‐10 Hz discontinuities are produced by a pulsatile descending motor command, the coding of the periodic but tenuous kinematic events by the population of proprioceptors may have a role in relation to an alleged pulsatile command generator.

Lighter or Heavier Than Predicted: Neural Correlates of Corrective Mechanisms during Erroneously Programmed Lifts

“…Thus, the M1 activity in question reflects the corrective force increase during the unpredictable weight change and not the total force output. Slow movements of the fingers are characterized by 8 -10 Hz discontinuities (Vallbo and Wessberg, 1993;Wessberg and Vallbo, 1995) to which muscle spindles vigorously respond, and these discontinuities were also observed in this study (Fig. 1, grip force rate profile).…”

Cortico-muscular synchronization by proprioceptive afferents from the tongue muscles during isometric tongue protrusion

“…Previous studies have reported that CMC was detected at low-frequency band (Wessberg and Vallbo, 1995;Gross et al, 2002) during repetitive slow finger movements. Recent CKC studies also detected the coupling between the cortex and finger at the low-frequency band of repetitive finger movements (Piitulainen et al, 2013a(Piitulainen et al, , 2013bBourguignon et al, 2015).…”

Experimental muscle pain increases normalized variability of multidirectional forces during isometric contractions

“…Inhibitory pathways converging into group Ia afferents decrease excitatory input to alpha-motoneurons, hence modulating force fluctuations (Yoshitake et al 2004;Shinohara et al 2005). In addition, spatial facilitation between group III and IV muscle afferents and Ib afferents may modulate the sensitivity of muscle tension control by decreased reflex sensitivity in agonist muscles and increased reflex sensitivity in antagonist muscles (Graven-Nielsen et al 2002), modifying the ability of the central nervous system to interpret proprioceptive information needed to precisely control force or position of the limbs (Wessberg and Vallbo 1995). Third, increased synchronization of motor units may have contributed to higher force fluctuations (Yao et al 2000).…”