Submitted on April 6, 2008
Revised on August 24, 2008
Accepted on August 28, 2008
DSCF Neurons within the Primary Auditory Cortex of the Mustached Bat Process Frequency Modulations Present within Social Calls
Stuart D Washington1* and Jagmeet S Kanwal2
1 Georgetown University Medical Center
2 Georgetown University
* To whom correspondence should be addressed. E-mail: sdw4{at}georgetown.edu.
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 (BFlow and BFhigh, respectively) facilitates its response. BFlow corresponds to a frequency in the frequency modulated (FM) component of the first harmonic in the echolocation pulse and BFhigh 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 BFhigh region to arrive at the "best FM" for single DSCF neurons. We report that DSCF neuron responses to linear FMs did not significantly differ (p=0.08) from responses to BFhigh when either stimulus is paired with the BFlow. For linear FMs ranging in slope from 0.04-4.0 kHz/ms and in bandwidth from 0.44-7.88 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 BFhigh. Neurons exhibited combination-sensitivity to "call fragments" (calls that were bandpass filtered in the BFhigh region) that were paired with their BFlow. 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 demonstrate that DSCF neurons extract multiple parameters of FMs and are specialized for processing both FMs, for communication, and CFs, for echolocation.
