Target Range Processing Pathways in the Auditory System of the Mustached Bat
Echolocating bats determine target range from the time interval between emitted sonar pulses and returning echoes. Long CF-FM bats determine range using cues provided by the FM components of their signals (Simmons, 1973). The mustached bat emits pulses consisting of four harmonics each containing a long constant frequency (CF) component followed by a brief, descending FM. Suga and his colleagues have shown that there are neurons in at least two fields of auditory cortex (FM-FM and DF) which only respond to second (FM2), third (FM3), or fourth (FM4) harmonic FM stimuli when preceded at a specific time interval by a first harmonic (FM1) stimulus (O’Neill & Suga, 1982; Suga et al., 1983; Suga, 1984). Each of these “FM-FM” neurons is tuned to a specific, or best, time delay, and the cortical fields in which they are located are organized by increasing best delay (“chronotopic” axis) in the rostrocaudal direction. Thus, there are at least two neural axes representing target distance (“odotopic axes”) in each hemisphere of the auditory cortex of the mustached bat.
KeywordsAuditory Cortex Inferior Colliculus Good Frequency Single Unit Recording Medial Geniculate Body
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