Corticomotoneuronal Postspike Effects in Shoulder, Elbow, Wrist, Digit, and Intrinsic Hand Muscles During a Reach and Prehension Task

Abstract

We used spike-triggered averaging of rectified electromyographic activity to determine whether corticomotoneuronal (CM) cells produce postspike effects in muscles of both proximal and distal forelimb joints in monkeys performing a reach and prehension task. Two monkeys were trained to perform a self-paced task in which they reached forward from a starting position to retrieve a food reward from a small cylindrical well. We compiled spike-triggered averages from 22 to 24 separate forelimb muscles at both proximal (shoulder, elbow) and distal (wrist, digits, intrinsic hand) joints. Of 174 cells examined, 112 produced postspike effects in at least one of the target muscles. Of those cells, 45.5% produced postspike effects in both proximal and distal forelimb muscles. A nearly equal number (44.7%) produced postspike effects in distal muscles only, whereas a clear minority (9.8%) produced postspike effects in only proximal muscles. The majority of CM cells (71.4%) produced effects in two or more muscles, with an average muscle field of 3.1 +/- 2.1 (mean +/- SD) for facilitation plus suppression. Of 345 postspike effects identified, 70.7% were facilitation effects and 29.3% were suppression effects. The large majority of effects (72.2%) were in distal muscles. When averaged by joint, the latency and peak magnitude of postspike facilitation showed a stepwise increase from proximal to distal joints. The results of this study show that the majority of CM cells engaged in coordinated forelimb reaching movements facilitate and/or suppress muscles at multiple joints, including muscles at both proximal and distal joints. The results also show that CM cells make more frequent and more potent terminations in motoneuron pools of distal compared with proximal muscles.

Modelling the control of interceptive actions

“…monoarticular flexor and biarticular extensor), which would have been equally valid from a FLETE perspective and is also consistent with the existence of single corticospinal projections to ␣-motor neurons of several muscles (e.g. McKiernan et al 1998;Holdefer & Miller 2002) as well as with the spinal coding of muscle synergies defined in terms of their angular equilibrium point (e.g. Bizzi et al 1991;Saltiel et al 2001).…”

Congenitally altered motor experience alters somatotopic organization of human primary motor cortex

“…However, this phenomenon has only been observed within extremities, but not across upper and lower extremities (37). Corticomotoneuronal cells with monosynaptic connections to different finger muscles have been found throughout the whole arm area including areas known to contain the shoulder representation, but not beyond (3,4).…”

Absence of a proximal to distal gradient of motor deficits in the upper extremity early after stroke

“…Based on this clinical perception, it is often presumed that the loss of distal segment movement is responsible for the loss of hand function after stroke (Muellbacher et al, 2002). The perception is consistent with disruption to the corticospinal system which is known to have greater input to distal cervical motoneuron pools compared to proximal cervical motoneuron pools (Palmer and Ashby, 1992;Porter and Lemon, 1993;McKiernan et al, 1998;Turton and Lemon, 1999). Indeed, the severity of motor deficits post stroke is strongly related to the degree of corticospinal system damage (Pineiro et al, 2000).…”

“…It has been thought that the proximal to distal gradient in movement deficits stems from disruption of this system, which sends more numerous projections to the distal cervical motoneuron pools (Palmer and Ashby, 1992;Porter and Lemon, 1993;McKiernan et al, 1998;Turton and Lemon, 1999). If compensatory control was exerted by other descending motor pathways, e.g.…”