The Binaural Interaction Component in Barn Owl (Tyto alba) Presents few Differences to Mammalian Data

Abstract

The auditory brainstem response (ABR) is an evoked potential that reflects the responses to sound by brainstem neural centers. The binaural interaction component (BIC) is obtained by subtracting the sum of the monaural ABR responses from the binaural response. Its latency and amplitude change in response to variations in binaural cues. The BIC is thus thought to reflect the activity of binaural nuclei and is used to non-invasively test binaural processing. However, any conclusions are limited by a lack of knowledge of the relevant processes at the level of individual neurons. The aim of this study was to characterize the ABR and BIC in the barn owl, an animal where the ITD-processing neural circuits are known in great detail. We recorded ABR responses to chirps and to 1 and 4 kHz tones from anesthetized barn owls. General characteristics of the barn owl ABR were similar to those observed in other bird species. The most prominent peak of the BIC was associated with nucleus laminaris and is thus likely to reflect the known processes of ITD computation in this nucleus. However, the properties of the BIC were very similar to previously published mammalian data and did not reveal any specific diagnostic features. For example, the polarity of the BIC was negative, which indicates a smaller response to binaural stimulation than predicted by the sum of monaural responses. This is contrary to previous predictions for an excitatory-excitatory system such as nucleus laminaris. Similarly, the change in BIC latency with varying ITD was not distinguishable from mammalian data. Contrary to previous predictions, this behavior appears unrelated to the known underlying neural delay-line circuitry. In conclusion, the generation of the BIC is currently inadequately understood and common assumptions about the BIC need to be reconsidered when interpreting such measurements.

Development of auditory sensitivity in the barn owl

“…7). These thresholds are comparable to, but greater than the 5–10 dB thresholds recorded for binaural chirp stimuli by Palanca-Castan et al (2016).…”

“…6) (Brittan-Powell and Dooling 2004; Brittan-Powell et al 2005, Palanca-Castan et al 2016). Note that the origins of ABR components are currently under study (Palanca-Castan et al 2016). Adult ABRs showed average thresholds between 11–15 dB SPL for 2 – 8 kHz tones (* in Fig.…”

“…The 8th nerve is myelinated before time of hatching, but myelination of NM and NL axons was only complete about a month after hatching (Cheng and Carr 2007), suggesting that later components of ABR waveforms may depend on both peripheral and central development. Later ABR peaks were not analyzed here, but contributions from the hindbrain auditory nuclei may be represented in peaks 2 and later of the ABR signal in budgerigars (Brittan-Powell et al 2002) and barn owls (Palanca-Castan et al 2016). Myelination and growth in the auditory brainstem is not uniform, but follows the tonotopic axes of all structures (Carr and Boudreau 1996).…”

“…A conference proceeding showed representative ABR traces in developing barn owls (Carr et al 1997), and Palanca-Castan et al (2016) measured the binaural interaction components of the ABR to chirps and to 1 and 4 kHz tones in adult barn owls. ABRs were thoroughly evaluated in adult screech owls ( Megascops asio ) (Brittan-Powell et al 2005).…”

Dipolar extracellular potentials generated by axonal projections

“…One such signal is the auditory brainstem response (ABR), which is recorded at the scalp in response to auditory stimulation with clicks or chirps (Riedel and Kollmeier, 2002). The amplitude of about 10 µV of the ABR in the barn owl has recently been reported by Palanca-Castan et al (2016). We calculated the contribution expected from an axon bundle with the same characteristics as described before at 2 cm from NL, aiming to estimate the contribution to the ABR.…”