THE CENTRAL AUDITORY PATHWAY

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Abstract
Unipolar recordings of responses to click stimuli were taken from various stations along the auditory pathway in anesthetized cats. Monaural and binaural stimulation were employed, and parts of the pathway were deleted surgically in some of the expts., followed by recording of changes from normal responses at the several electrode stations, demonstrating elimination of various coir ponents. Latency of response increases at successively higher levels, making possible presumptive detn. of number of synapses to a given point. Duration and amplitude of response also increases at successively higher levels, indicating progressive temporal dispersion. This is accompanied by a progressive tendency toward smoothing of the wave form as more and more elements are activated at each higher level and their summed potentials merge, obscuring the identity of the various contributions. Difference in latency of response of inferior colliculus to ipsilateral and contralateral stimulation plus difference in the earliest peak or shoulder of the collicular and brachial responses indicate one more synapse in the ipsi-lateral pathway than in the contralateral. Second-order fibers form the chief contralater.-.l component up to midbrain level, while the earliest ipsilateral midbrain response is that of 3d-order fibers. At thalamic and cortical stations, this difference is compensated by longer nuclear delays. The trapezoid body is by far the most important site of crossing in the cortical projection pathway for hearing. The commissure of the inferior colliculus may contribute slight additional opportunity for decussation, but is more probably principally concerned in com-missural communication necessary to integrative processes at midbrain level.

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