Bilateral spike-triggered average effects in arm and shoulder muscles from the monkey pontomedullary reticular formation

Pontomedullary reticular formation (PMRF) neurons (309) were recorded simultaneously with electromyographic activity from arm and shoulder muscles in four monkeys performing arm-reaching tasks. Spike-triggered averages (SpikeTAs) were compiled for 292 neurons (3836 neuron-muscle pairs). Fourteen PMRF neurons located in a region ventral to the abducens nucleus produced 42 significant SpikeTA effects in arm and shoulder muscles. Of these 14 PMRF neurons, nine produced SpikeTA effects bilaterally. Overall, PMRF neurons facilitated ipsilateral flexors and contralateral extensors, while suppressing ipsilateral extensors and contralateral flexors. Spike- and stimulus-triggered averaging effects obtained from the same recording site were similar. These findings indicate that single PMRF neurons can directly influence movements of both upper limbs.