New perspectives on spinal motor systems.

Bizzi E, Tresch MC, Saltiel P, d'Avella A

Nat Rev Neurosci 2000 Nov;1(2):101-8

The role of the spinal cord

The production and control of complex motor functions are usually attributed to central brain structures such as cortex, basal ganglia and cerebellum. In traditional schemes the spinal cord is assigned a subservient function during the production of movement, playing a predominantly passive role by relaying the commands dictated to it by supraspinal systems. This review challenges this idea by presenting evidence that the spinal motor system is an active participant in several aspects of the production of movement, contributing to functions normally ascribed to 'higher' brain regions.

Isometric force fields

Bizzi et al. 1991

Smooth fields

The dynamics

Mussa-Ivaldi et al. 1990

3D forcefields in the rat spinal cord

Summation of force fields

F(x1) F(x2)

F(x1) + F(x2) F(x1+x2)r > 0.9

Mussa-Ivaldi et al. 1994

Control I: Iontophorese

P. SALTIEL, M.C. TRESCH & E. BIZZI, J. Neurophysiol., 2000

Taken together, these results support the concept of a modular organization of the motor system in the frog’s spinal cord and delineate the topography of these modules. They also suggest that these modules are used by the circuitry underlying rhythmic pattern generation by the spinal cord.

Control II: random activation

r median = 0.871

Loeb et al., J. Cog. Neurosci., 2000

Control II: random activation

Only few of the random activations leed to robust synergies

Loeb et al., J. Cog. Neurosci., 2000

Control III: Dimensionality

A. D’AVELLA AND E. BIZZI, PNAS, 1998

The involvement of spinal interneurons in the preparation for movement.

Y. Prut & E.E. Fetz, Nature, 1999

A comparison of different motor structures

Y. Prut & E.E. Fetz, Nature, 1999

The process of motor adaptation following ankle extensor nerve cut

The sensory side

G. Bosco, R.E. Poppele, & J. Eian, J. Neurophysiol. 2000

... We found that 14% neurons represented one or more specific joint angles. The activity of another 39% neurons was significantly affected by limb geometry changes, but 47% consistently elaborated a foot position represen-tation in the coordinates of the limb axis.

The end

Muscle activation patterns