Fig. 1 | Nature Communications

Fig. 1

From: Precisely timed inhibition facilitates action potential firing for spatial coding in the auditory brainstem

Fig. 1

ILD processing in the LSO requires high neuronal sensitivity to binaural input timing. a The acoustic head shadow produces location-specific interaural level differences (ILDs) between the ears. b Right: ILDs are first detected by LSO neurons by comparing ipsilateral excitatory input from the cochlear nucleus (CN) and contralateral inhibitory input from the medial nucleus of the trapezoid body (MNTB). Left: the recording site at the medial limb of the LSO for data shown in f was labeling with horseradish-peroxidase, which was deposited via the recording electrode. Scale bar: 500 µm. c During ILD computation, LSO neurons integrate the relative strength (amplitude) and timing of inhibitory and excitatory post-synaptic potentials (IPSPs and EPSPs, respectively). d Changes in the sound source location cause significant changes in the relative timing of the inputs to the LSO: higher absolute sound intensity cause PSPs with larger amplitude, and also shorter latencies. The graph (middle panel) illustrates these level-dependent changes in first spike latency of an auditory nerve fiber (adapted from63). Together with the location-specific ITD (in the range of <120 µs), these latency changes largely determine the range of input timing changes associated with changes in the location of a sound source (right panel). Thus, ILD computation also involves gauging of the relative timing of EPSPs and IPSPs. e The acoustic stimulus consisted of six clicks (50 µs duration per click), spaced at five different ICIs (1–5 ms in 1 ms increments). For binaural presentation, the cTD was varied between −400 and +400 µs in 200 µs steps (negative values denote ipsilateral ear leading stimuli). f Left: Mean spike rates per repetition from an example neuron (CF: 24.3 kHz) during (ipsilateral) excitatory only click train stimulation. (74 dB SPL, 20 repetitions each, ICIs color-coded as denoted in e. Right: cTD-response functions of the same neuron (ipsi: 74 dB SPL, contra: 79 dB SPL, 20 repetitions). Inset shows mean spike waveform. Filled circles and shaded areas denote mean and standard error of the mean (s.e.m.). Note that maximal response rates at +200 and +400 µs cTD exceed mean rates during excitatory only stimulation

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