[Responses of medullary and spinal neurons to simultaneous stimulation of two locomotor points]

Responses of neurons in the medulla and cervical segments to simultaneous repetitive (50 pps) stimulation of two locomotor points (LPs) by currents in the range of 1 to 2 thresholds of locomotion were studied. In most cases a neuron responded to stimulation of only one LP. Stimulation of the second LP enhanced usually the firing index of that response, if it was low, diminished it, if it was high and did not influence it, if it was about 0.2. Part of neurons increased the background activity during stimulation of one of LPs though spikes were not locked to stimuli. A sign of influence of the second LP onto that elevation depended on its value. Data about the convergence of inputs from the ipsi- and contralateral midbrain and bulbar LPs on single neurons were obtained too. Possible mechanisms of summation of subthreshold excitation of two LPs during initiation of the locomotion are discussed.