Auditory Activity in Uncrossed Centrifugal Gochlear Fibres in Cat A Study of a Feedback System, II

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Abstract
Fex, J., Auditory activity in uncrossed centrifugal cochlear fibres in cat. A study of a feedback system, II. Acta physiol. scand. 1965. 64. 43–57. – In decerebrate cats all of the cochlear efferents except the uncrossed olivo‐cochlear fibres were cut, the vestibulo‐cochlear anastomosis was exposed through the vestibule and single unit activity was recorded in, and close to, the anastomosis with micropipette electrodes. Although the auditory function was destroyed in the dissected cochlea, resting activity was found in primary auditory afferents, suggesting that synaptic mechanisms could still be intact in such a preparation. – Uncrossed olivo‐cochlear fibres were activated by electrical stimulation of the ipsilateral cochlear nerve and by acoustic stimulation of the contralateral ear. When activated by sound, the uncrossed efferents in the basal fascicle of the anastomosis generally responded to higher tone frequencies than did fibres in the apical fascicle, which suggests that afferents and uncrossed efferents from homotopic cochlear points in opposite cochleae are connected. The fibres responded characteristically with a low, regular firing rate without an initial burst and with a long latency at threshold, indicating that their input would be integrated over a considerable time. Many of the efferents showed resting activity which, with few exceptions, could be inhibited by sound depending on the choice of tone frequency. – The findings suggest that the uncrossed cochlear efferents and ipsilateral auditory afferents together form an auditory, closed feedback loop, which is directly influenced by the contralateral ear and support the hypothesis (Fex 1962) that the uncrossed and the crossed olivo‐cochlear bundles together form a complex, auditory feedback mechanism.

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