Gentner - 2006 - Modular organization of finger movements by the human central nervous system

Citation

Gentner R, Classen J. Modular organization of finger movements by the human central nervous system. Neuron. 2006 Nov 22;52(4):731-42. PUBMED

10 Word Summary

Finger movements are initiated by modular motor cortex commands.

Abstract

The motor system may generate automated movements, such as walking, by combining modular spinal motor synergies. However, it remains unknown whether a modular neuronal architecture is sufficient to generate the unique flexibility of human finger movements, which rely on cortical structures. Here we show that finger movements evoked by transcranial magnetic stimulation (TMS) of the primary motor cortex reproduced distinctive features of the spatial representation of voluntary movements as identified in previous neuroimaging studies, consistent with naturalistic activation of neuronal elements. Principal component analysis revealed that the dimensionality of TMS-evoked movements was low. Principal components extracted from TMS-induced finger movements resembled those derived from end-postures of voluntary movements performed to grasp imagined objects, and a small subset of them was sufficient to reconstruct these movements with remarkable fidelity. The motor system may coordinate even the most dexterous movements by using a modular architecture involving cortical components.

Notes

• The motor system may coordinate movements by using a modular architecture.
• Synergy - a set of neuromotor modules providing a basis for intentional and automatic actions.
• They point out that muscular organization was mostly classified in electrical stimulation of the spinal cords of frogs, and that similar experiments in spinalized cats did not corroborate these results.
  • The argument being that mammals store synergies in motor cortex, not the spinal cord.
• Movements were very small. Joint angles on the order of 2°
• Variability of TMS evoked movements was constrained by neuronal factors
• TMS evoked movements were modular in nature
• Structural similarity in PCA components between voluntary and TMS evoked movements.
• The main finding was that TMS evoked movements were significantly constrained in comparison to the biomechanics of the finger.
  • How did they test the dimensionality of the biomechanics of the finger?