Fig. 6
A functional role of post-inhibitory facilitation in the LSO. a Schematic of the stimulus design. Left: three ipsi sound intensities, normalized to the loudest (magenta ≙ 0 dB) were combined with a wide range of contra intensities. b Schematic of hypothetical ILD-response functions during soft (light brown) or loud (magenta) ipsilateral stimulation. Soft ipsi stimulation not only lowers spike rates at ipsi-favoring ILDs (blue arrow), but also increases the relative potency of the inhibition due to both amplitude and timing effects, resulting in a diminished dynamic range (steeper slope) under soft ipsilateral starting conditions. However, higher contra intensities are likely to cause the IPSP to precede the EPSP and thus generate PIF, which in turn can recover the dynamic range of the ILD-response function by an increase in spike probability along the slope (dark brown). c ILD-response functions of an example neuron (CF: ~16.2 kHz) in response to the three different ipsi conditions (color-coded) as introduced in a. Data are presented as mean ± s.e.m. d Changes in spike rates along the slopes of the ILD-response functions were only slightly affected by decreased ipsi intensities (−5 dB: −0.37% median change, interquartile range −2.75–0.24%; P = 0.22, Wilcoxon signed rank test; −10 dB: 13.0% median change, interquartile range −21.5 to −5.9%; P = 0.03, Wilcoxon signed rank test, n = 7 neurons). Inset: spike rates at identical ILDs were increased during reduced ipsi intensities (−5 dB: 4.4% median change, interquartile range: 1.9–14.3%, P = 0.03; −10 dB: 16.6% median change, interquartile range: −3.5–28.4%, P = 0.11, n = 7 cells). White horizontal bars show medians, interquartile range is given by box size; whiskers extend to most extreme data points. e Slope steepness remained unaltered between the three ipsi conditions (−5 dB: −3.1% median change, interquartile range: −16.6–9.8%, P = 0.81; −10 dB: −4.7% median change, interquartile range −19.6–11.4%, P = 0.81, n = 7 cells). Same conventions as in d. f Neuronal information about the separability of nearby ILDs was similar across ipsi conditions (P > 0.05 for all ILDs, t-test; solid lines and shaded areas show mean and s.e.m., respectively)
