Absence of tonic activity of the crossed olivocochlear bundle in determining compound action potential thresholds, amplitudes and masking phenomena in anaesthetised guinea pigs with normal hearing sensitivities

In Nembutal- or Urethane-anaesthetised guinea pigs A N₁ audiograms and N₁ input-output functions were measured as were compound action potential (CAP) tuning curves under forward masking and simultaneous masking conditions. Then the crossed olivocochlear bundle was lesioned at the floor of the fourth ventricle and the cochlear responses were re-measured. There were never any changes in the N₁ audiograms, input-output functions, or the CAP tuning curves. Thus, the crossed efferent pathways do not appear to play any tonic role in determining cochlear threshold sensitivities, selectivities or masking phenomena in anaesthetised guinea pigs with normal hearing sensitivities.