Effect of stimulus parameters on motor and respiratory responses to midbrain stimulation in unrestrained cats

Abstract

In cats with chroncially implanted electrodes, the effect of varied stimulus parameters has been assessed on head turning and respiratory responses to electrical stimulation of midbrain sites. Parameter variables included sustained trains vs. periodic bursts of pulses, varied shapes of bursts, and different pulse shapes. Differentiation of response components by stimulus parameters bore a direct relation to electrode location. With sites in the dorsolateral posterior midbrain tegmentum, head movements were evoked by any type of stimulation but respiratory concomitants were related to stimulus parameters. Stimulation of sites in the posterior tecto-tegmental region revealed selective effects of pulse shape on respiration vs. head turning. For sites at the lateral edge of the central gray matter, head turning could be evoked without respiratory changes, or respiration could be altered without head movement. Thus horizontal head turning was seen upon stimulation with sustained trains of square waves, while respiration became stimulus-bound upon stimulation with periodic bursts of modified square waves. With the latter stimulus, respiration was altered to one respiratory cycle per stimulus burst, regardless of the spontaneous prestimulus respiration rate. The phase of the respiratory cycle correlated with onset of stimulus burst, although constant throughout one stimulus, was not the same for a series of responses to stimulation of one site. With sampling of a wide range of stimulus parameters, it was possible to differentiate somatomotor from respiratory components to stimulation of sites in a restricted area of the dorsal midbrain.