ELECTRIC RESPONSES OF THE BRAIN STEM TO UNILATERAL AUDITORY STIMULATION

Abstract

Action potentials were recorded from the trapezoid fibers and lateral lemniscus of the cat. With tonal stimuli synchronized responses were obtained at frequencies up to 2500 c.p.s. from the trapezoid fibers and about 1000 c.p.s. from the lateral lemniscus. The increase in amplitude of responses with increasing intensity of stimulation indicated that activation of additional fibers was the physiological basis for increasing loudness. Responses from trapezoid fibers appeared 1.3 to 2.0 msec. and responses from the lateral lemniscus appeared 2.3 to 3.1 msec. after corresponding 8th nerve potentials. Subtraction for conduction time left 0.8 msec. for synaptic delay in the coehlear nuclei and 0.8 msec. for synaptic delay in the superior olive. Separate components of the complex click response might be masked by simultaneous stimulation with tones of correct frequencies. The best explanation of this fact was in terms of the place theory.