Proceedings of the 29th Göttingen Neurobiology Conference, 330, p.433, 2003.

Signal analysis of neurophonic responses in the owl's nucleus laminaris

H. Wagner¹ ², S. Brill¹, R. Kempter³, and C. E. Carr²

¹ Institute for Biology II, RWTH Aachen, Germany
² Department of Biology, University of Maryland, College Park, USA
³ Institute for Theoretical Biology, Humboldt University Berlin, Germany

Clicks are powerful stimuli for studying auditory processing, because they allow for a characterization of the transfer properties of a system. Nucleus laminaris in the barn owl contains a network composed of axonal delay lines and coincidence-detection neurons that underlies the extraction of an important sound-localization parameter, the interaural time difference (ITD).

To study the properties of the neural network in the nucleus laminaris, we recorded the neurophonic potential in 7 anesthetized barn owls. Clicks, noises and tones were used as stimuli. Frequency tuning curves, ITD tuning curves, and click response curves were determined. Clicks varied in duration (20-80 microseconds), level (0 to 60 dB attenuation), and polarity (rarefaction or condensation). The median of the responses to typically 128 repetitions was analyzed.

The click-evoked neurophonic responses in nucleus laminaris exhibited oscillations with several frequency components, usually one or two prominent low-frequency (< 2kHz) components and a high-frequency (> 2kHz) component. Only the high-frequency component was further analyzed, because it was close to the frequency tuning measured with tones. The responses were fitted well by either a Gabor or a Gammatone function. Each of these functions is characterized by 6 parameters. It was tested how the three stimulus parameters level, duration and polarity influence the 6 fit parameters amplitude, width, frequency, offset, latency and phase. A decrease in click level led to a decrease in amplitude, and increases in latency and frequency. Click duration had little effect on the response. Rarefaction clicks had shorter latencies that condensation clicks. These data provide an important precondition for the understanding of the laminaris network in sound localization.