In vitro analysis of optimal stimuli for phase-locking and time-delayed modulation of firing in avian nucleus laminaris neurons

Abstract

Neurons of the avian nucleus laminaris (NL) provide a neural substrate for azimuthal sound localization. We examined the optimal stimuli for NL neurons to maintain high discharge rates, reliable phase-locking, and sensitivity to time-delayed stimuli. Whole-cell recordings were performed in chick [embryonic days 19-21 (E19-E21)] NL neurons using an in vitro slice preparation. Variation of membrane properties along the tonotopic axis was examined. Computer-controlled intracellular current injection was used to mimic postsynaptic currents or conductances (PSCs) generated in NL neurons by the firing of nucleus magnocellularis (NM) neurons during acoustic stimulation. At various stimulus frequencies, the effects of varying the number of NM cells and PSC amplitudes on firing rate and phase-locking were examined. During high-frequency stimulation, the greatest firing rate and phase-locking occurred when the protocol contained few NM cells that generated large PSCs. Because the stimulus-evoked unitary PSCs are small, we propose that NM cells fire in synchrony to generate large PSCs. To mimic the arrival of PSCs during binaural stimulation, two stimulus trains were summed at different delays before injection. The firing rate of NL neurons was greatest with zero delay. A delay of half the stimulus period evoked firing that was less than that evoked with a single train. Neurons lacking strong outward rectification exhibited neither reliable phase-locking during high-frequency stimulation nor sensitivity to stimulus delays. These findings suggest that the firing responses of NL neurons are determined primarily by their membrane properties.

Coincidence detection in the Hodgkin–Huxley equations

“…at around f S =1 kHz. Indeed, maximal vector strength, r, is inversely proportional to the main sound frequency, f S , as confirmed in experiment in hen, barn owl and dog (Goldberg and Brown, 1969;Konishi, 1990;Reyes et al, 1996). For experimental data, see fig.…”

“…V is normalized to get max V= 1 for minimal Dt=0,~= 2 ms, in the Eq. (1), and h= 3 ms − 1 , from Reyes et al (1996). Note that the position of maximal slope in this curve is comparable with the time constant.…”

“…For experimental data, see fig. 6A in Reyes et al (1996). All experimental data showing the inverse proportion lie in the region given by r5~f S − 1 , where~= 1 ms, therefore, f S is in kHz.…”

“…This model was designed as the simplest possible HH-type model reflecting the values of experimental quantities directly in its parameters. We use here a remake of this model by Agmon-Snir et al (1998) based on experimental data from chicken-brain slices by Reyes et al (1994Reyes et al ( , 1996. The complete set consists of, 1.…”

Coding interaural time differences at low best frequencies in the barn owl

“…Coincidence detectors exhibit low threshold K þ conductances that lead to a single or few well-timed spikes in response to a depolarizing stimulus in vitro [92,106]. These conductances act to decrease the effective membrane time constant i.e.…”