Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii.
Pteronotus parnellii uses the second harmonic (61-62 kHz) of the CF component in its orientation sounds for Doppler-shift compensation. The bat's inner ear is mechanically specialized for fine analysis of sounds at about 61-62 kHz. Because of this specialization, cochlear microphonics (CM) evoked by 61-62 kHz tone bursts exhibit prominent transients, slow increase and decrease in amplitude at the onset and cessation of these stimuli. CM-responses to 60-61 kHz tone bursts show a prominent input-output non-linearity and transients. Accordingly, a summated response of primary auditory neurones (N1) appears not only at the onset of the stimuli, but also at the cessation. N1-off is sharply tuned at 60-61 kHz, while N1-on is tuned at 63-64 kHz, which is 2 kHz higher than the best frequency of the auditory system because of the envelope-distortion originating from sharp mechanical tuning. Single peripheral neurones sensitive to 61-62 kHz sounds have an unusually sharp tuning curve and show phase-locked responses to beats of up to 3 kHz. Information about the frequencies of Doppler-shifted echoes is thus coded by a set of sharply tuned neurones and also discharges phase-locked to beats. Neurones with a best frequency between 55 and 64 kHz show not only tonic on-responses but also off-responses which are apparently related to the mechanical off-transient occuring in the inner ear and not to a rebound from neural inhibition.
D000200:Action Potentials; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D001309:Auditory Threshold / Q000502:physiology; D002685:Chiroptera / Q000502:physiology*; D003051:Cochlea / Q000502:physiology; D004301:Doppler Effect; D004429:Ear Ossicles / Q000502:physiology; D007758:Ear, Inner / Q000502:physiology; D004432:Ear, Middle / Q000502:physiology; D004455:Echolocation / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D009433:Neural Inhibition; D009949:Orientation / Q000502:physiology*; D000159:Vestibulocochlear Nerve / Q000502:physiology