Tonotopic Specialization of Auditory Coincidence Detection in Nucleus Laminaris of the Chick

Abstract

The interaural time difference (ITD) is a cue for localizing a sound source along the horizontal plane and is first determined in the nucleus laminaris (NL) in birds. Neurons in NL are tonotopically organized, such that ITDs are processed separately at each characteristic frequency (CF). Here, we investigated the excitability and coincidence detection of neurons along the tonotopic axis in NL, using a chick brainstem slice preparation. Systematic changes with CF were observed in morphological and electrophysiological properties of NL neurons. These properties included the length of dendrites, the input capacitance, the conductance of hyperpolarization-activated current, and the EPSC time course. In contrast to these gradients, the conductance of low-threshold K ϩ current and the expression of Kv1.2 channel protein were maximal in the central (middle-CF) region of NL. As a result, the middle-CF neuron had the smallest input resistance and membrane time constant, and consequently the fastest EPSP, and exhibited the most accurate coincidence detection. The specialization of middle-CF neurons as coincidence detectors may account for the high resolution of sound-source localization in the middle-frequency range observed in avians.

Posthearing Developmental Refinement of Temporal Processing in Principal Neurons of the Medial Superior Olive

“…However, unlike in chick nucleus laminaris (Smith and Rubel, 1979;Kuba et al, 2005), we did not find electrophysiological or morphological changes along the putative tonotopic axis in the MSO. The reason that electrical maturity is Figure 5.…”

Diversity of Gain Modulation by Noise in Neocortical Neurons: Regulation by the Slow Afterhyperpolarization Conductance

“…The f-I relationships were plotted based on the last 200 ms of 230 ms stimuli. As shown previously (Reyes et al, 1996;Kuba et al, 2005), NL cells did not fire to constant current without noise. With sufficient noise rising and falling f-I relationships were obtained, and the gain and maximal firing rate increased with noise amplitude (Fig.…”

“…To explore the generality of this result for neuronal coincidence detectors, we obtained f-I relationships for noisy current steps in neurons from chick nucleus laminaris (NL), which encode sound source location as the firing rate by detecting coincident signals from ipsilateral and contralateral afferents (Jeffress, 1948;Carr and Konishi, 1990). Because the EPSCs that these cells receive have extremely fast kinetics (Reyes et al, 1996;Kuba et al, 2005), we used noise with a fast time constant ( ϭ 0.2 ms) rather than the slower noise applied to cortical neurons ( ϭ 3 ms). The f-I relationships were plotted based on the last 200 ms of 230 ms stimuli.…”

Modeling Binaural Responses in the Auditory Brainstem to Electric Stimulation of the Auditory Nerve

“…Alternatively, the stronger inward I h measured in neurons with higher CFs could raise the membrane potential and, thus, increase the KLT conductance via activation of a greater number ion channels, producing qualitatively similar results to those presented in this manuscript, even in the absence of a tonotopic gradient in KLT channel density. A systematic dependence of K + channel expression on tonotopic location has been reported for nucleus laminaris (NL), the avian homologue of MSO (Kuba et al 2005(Kuba et al , 2006Hamlet et al 2014). NL further shows tonotopic gradients in many other cellular properties, including densities of Na + and I h channels as well as metabotropic glutamate receptors (Ohmori 2014).…”