LINEAR-COMBINATIONS OF PRIMITIVES IN VERTEBRATE MOTOR CONTROL

Recent investigations on the spinalized frog have provided evidence su ggesting that the neural circuits in the spinal cord are organized int o a number of distinct functional modules. We have investigated the ru le that governs the coactivation of two such modules. To this end, we have developed an experimental paradigm that involves the simultaneous stimulation of two sites in the frog's spinal cord and the quantitati ve comparison of the resulting mechanical response with the summation of the responses obtained from the stimulation of each site. We found that the simultaneous stimulation of two sites leads to the vector sum mation of the endpoint forces generated by each site separately. This linear behavior is quite remarkable and provides strong support to the view that the central nervous system may generate a wide repertoire o f motor behaviors through the vectorial superposition of a few motor p rimitives stored within the neural circuits in the spinal cord.