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

Abstract

Washington SD, Kanwal JS. DSCF neurons within the primary auditory cortex of the mustached bat process frequency modulations present within social calls. J Neurophysiol 100: 3285-3304, 2008. First published September 3, 2008 doi:10.1152/jn.90442.2008. 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 ϭ 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.

Sex-dependent hemispheric asymmetries for processing frequency-modulated sounds in the primary auditory cortex of the mustached bat

“…Surgical and recording methods were previously described Medvedev and Kanwal 2004;Washington and Kanwal 2008). We used 10 (6 male and 4 female) wild-caught mustached bats.…”

“…CFs were generated using custom-made analog function generators. A customized SIGNAL 3.0 script (Engineering Design) was used to generate FMs (Washington and Kanwal 2008). All CFs were 30 ms in duration, including 0.5-ms rise and fall times of amplitude.…”

“…We presented FMs from a leaf-tweeter speaker (Panasonic) that was flat (Ϯ3 dB SPL) from 5 to 100 kHz, which did not generate a significantly wideband click at DSCF neurons' preferred stimulus amplitudes (Ͻ80 dB SPL). Moreover, DSCF neurons are tuned to a narrow range of frequencies and can discriminate between 2-ms-long FMs presented in the upward vs. downward direction (see data supplement, Washington and Kanwal 2008).…”

“…Multifunctional neurons within its AC respond to constant frequencies (CFs) and FMs that are present not only in echolocation signals but also in the rich variety of communication sounds (or social calls) emitted by this species (Esser et al 1997;Kanwal et al 1994Kanwal et al , 1999Washington and Kanwal 2008). CFs and FMs in social calls of bats and other mammalian species are acoustically analogous to formants and formant transitions in human speech (Kanwal and Rauschecker 2007;Liberman et al 1956;Rauschecker and Scott 2009;Suga 1992).…”

“…All recordings were obtained from the Doppler-shifted CF processing (DSCF) area, which encompasses nearly half of A1 in this species (Kanwal 1999;Suga and Jen 1976;Xiao and Suga 2002) and has been shown to process both CFs and FMs (Washington and Kanwal 2008). We used both male and female bats to test for hemispheric differences within and between sexes.…”