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DSCF Neurons Within the Primary Auditory Cortex of the Mustached Bat Process Frequency Modulations Present Within Social Calls

Department of Physiology and Biophysics, Georgetown University Medical Center, Washington, DC

Submitted 6 April 2008; accepted in final form 28 August 2008

Neurons in the Doppler-shifted constant frequency processing (DSCF) area in the primary auditory cortex of mustached bats, Pteronotus parnellii, are multifunctional, responding both to echolocation and communication sounds. Simultaneous presentation of a DSCF neuron's best low and high frequencies (BF_low and BF_high, respectively) facilitates its response. BF_low corresponds to a frequency in the frequency-modulated (FM) component of the first harmonic in the echolocation pulse, and BF_high corresponds to the constant frequency (CF) component in the second harmonic of the echo. We systematically varied the slopes, bandwidths, and central frequencies of FMs traversing the BF_high region to arrive at the "best FM" for single DSCF neurons. We report that nearly half (46%) of DSCF neurons preferred linear FMs to CFs and average response magnitude to FMs was not significantly less (P = 0.08) than that to CFs at BF_high when each test stimulus was paired with a CF at BF_low. For linear FMs ranging in slope from 0.04 to 4.0 kHz/ms and in bandwidth from 0.44 to 7.88 kHz, the majority of DSCF neurons preferred upward (55%) to downward (21%) FMs. Central frequencies of the best FMs were typically close to but did not always match a neuron's BF_high. Neurons exhibited combination-sensitivity to "call fragments" (calls that were band-pass filtered in the BF_high region) paired with their BF_low. Our data show a close match between the modulation direction of a neuron's best FM and that of its preferred call fragment. These response properties show that DSCF neurons extract multiple parameters of FMs and are specialized for processing both FMs for communication and CFs for echolocation.