Strategies that simplify the control of quadrupedal stance. II. Electromyographic activity.

1. This study tested the hypothesis that muscle synergies underlie the invariance in the direction of corrective forces observed following stance perturbations in the horizontal plane. Electromyographic activity was recorded from selected forelimb and hindlimb muscles of cats subjected to horizontal translations of the supporting surface in 16 different directions. The responses of muscles were quantified for each perturbation, and tuning curves were constructed that related the amplitude of muscle response to the direction of platform movement. 2. Muscle tuning curves tended to group into one of two regions, corresponding to the two directions of force vectors. A few muscles showed clearly different recruitment patterns. The same direction of correction force vector was produced by different patterns of muscle activity, and the particular EMG pattern depended on the direction of platform movement. Therefore a simple muscle synergy organization could not account for the invariance in force vector generation. 3. It is concluded that there is a hierarchy of control in the maintenance of stance in which the vector of force exerted against the ground is a high level, task-dependent controlled variable and the selection of muscles to activate in order to produce the vector is controlled at a lower level. It is proposed that muscles are controlled using a modified synergy strategy. In this scheme, a synergy is not simply a fixed group of muscles, constrained to act as a unit. Rather, muscles are organized as a task-dependent synergy that is tuned or modified as needed by the addition or subtraction of other muscles.

[1]  Peter H. Greene,et al.  Problems of Organization of Motor Systems , 1972 .

[2]  Michael J. O'Donovan,et al.  Cat hindlimb motoneurons during locomotion. III. Functional segregation in sartorius. , 1987, Journal of neurophysiology.

[3]  B R Botterman,et al.  Localization of monosynaptic Ia excitatory post‐synaptic potentials in the motor nucleus of the cat biceps femoris muscle. , 1983, The Journal of physiology.

[4]  A. English,et al.  An anatomical and functional analysis of cat biceps femoris and semitendinosus muscles , 1987, Journal of morphology.

[5]  S. Grillner,et al.  Peripheral control of the cat's step cycle. I. Phase dependent effects of ramp-movements of the hip during "fictive locomotion". , 1981, Acta physiologica Scandinavica.

[6]  W. D. Letbetter,et al.  Anatomy and innervation patterns of cat lateral gastrocnemius and plantaris muscles. , 1982, The American journal of anatomy.

[7]  F. Horak,et al.  Influence of stimulus parameters on human postural responses. , 1988, Journal of neurophysiology.

[8]  S. Rossignol,et al.  On the initiation of the swing phase of locomotion in chronic spinal cats , 1978, Brain Research.

[9]  J. Macpherson.  Strategies that simplify the control of quadrupedal stance. I. Forces at the ground. , 1988, Journal of neurophysiology.

[10]  W. Rymer,et al.  Characteristics of synergic relations during isometric contractions of human elbow muscles. , 1986, Journal of neurophysiology.

[11]  D. W. Lywood,et al.  A system for the analysis of posture and stance in quadrupeds , 1987, Journal of Neuroscience Methods.

[12]  S. Grillner,et al.  Peripheral control of the cat's step cycle. II. Entrainment of the central pattern generators for locomotion by sinusoidal hip movements during "fictive locomotion.". , 1983, Acta physiologica Scandinavica.

[13]  Wynne A. Lee,et al.  Neuromotor synergies as a basis for coordinated intentional action. , 1984, Journal of motor behavior.

[14]  Elliot Saltzman,et al.  Levels of sensorimotor representation , 1979 .

[15]  W. D. Letbetter,et al.  A histochemical analysis of identified compartments of cat lateral gastrocnemius muscle , 1982, The Anatomical record.

[16]  Joshua R. Smith,et al.  Text-Atlas of Cat Anatomy , 1970 .

[17]  Easton Ta.  On the normal use of reflexes. , 1972 .

[18]  M. T. Turvey,et al.  Issues in the theory of action : Degree of freedom, coordinative structures and coalitions , 1978 .

[19]  S. Grillner,et al.  Peripheral feedback mechanisms acting on the central pattern generators for locomotion in fish and cat. , 1981, Canadian journal of physiology and pharmacology.

[20]  N. A. Bernshteĭn.  The co-ordination and regulation of movements , 1967 .

[21]  P H Ellaway,et al.  Cumulative sum technique and its application to the analysis of peristimulus time histograms. , 1978, Electroencephalography and clinical neurophysiology.