Article Figures & Data
Figures
- Fig. 1.
ITD and ILD tuning. ICx neurons are tuned to combinations of ITD and ILD. The ITD (a) or ILD (b) curve of a neuron is obtained by presenting different values of one cue while the most favorable value of the other cue is held constant. Sample intracellular traces show how the same neuron responded to different combinations of ITD and ILD. Values of ITD and ILD are shown above each trace. Error bars indicate SEM over five trials of each stimulus. Calibration: 10 mV, 50 msec.
- Fig. 2.
Transformations in auditory spatial receptive fields. Receptive fields measured by spiking rate showed either a single tall peak (b) or one tall (main) peak plus smaller side peaks, as in most neurons (a). However, the receptive fields (brown surfaces) measured in subthreshold PSPs had multiple peaks of similar amplitude surrounded by areas of hyperpolarization below the resting potential (bluesurfaces) (c, d). This difference is partly because of a mechanism that converts small differences in membrane potentials to large changes in spike rates (e). In addition, thresholding (green surface represents mean spike threshold measured from membrane potential records) greatly contributes to the isolation of the main peak from other peaks (f). Data in each row came from the same neuron.
- Fig. 3.
Changes in ITD and ILD tuning. a, ITD curves of spike rates show one large main peak in spike rate (top), whereas PSPs show side peaks and areas of hyperpolarization flanking the main peak (bottom).b, ILD curves are narrow and pyramid-shaped in spike rate (top) and broader in PSPs (bottom) for the same neuron. Error bars indicate SEM. Dotted lines represent the mean spontaneous discharge or mean resting potential.
- Fig. 4.
Sharpening of ITD and ILD tuning. This figure shows, for each neuron, the ITD and ILD tuning width and tuning ratio measured in PSPs and spike rates. a, The width of the main peak of ITD (filled circles) and ILD (open circles) tuning curves is narrower in spike rates than in PSPs. b, For both ITD (filled circles) and ILD (open circles), the tuning ratio in spike rates is significantly larger (i.e., narrower tuning) than in PSPs. The dashed line in eachpanel would result if the tuning width or ratio were the same for spike rates and PSPs.
- Fig. 5.
Symmetry and asymmetry in ILD curves. ILD curves measured in spikes (a) tend to be more symmetrical than their respective PSP curves (b). Error bars indicate SEM. Dotted lines represent the mean spontaneous discharge or mean resting potential. c, Distribution of symmetry indices for spikes and PSPs.
- Fig. 6.
Spiking threshold. a, Automatic computation of thresholds in four overlaid traces from a single neuron.Circles indicate the threshold for each spike. Thearrowhead indicates the onset spikes in the response induced by sound. The thresholds of all onset spikes fall below the mean threshold of spontaneous spikes (solid line). Sound stimulation starts at 100 msec.b, Plot of the spike threshold versus the rate of depolarization (dVm/dt) of the same neuron as ina. The threshold is lower when the rate of the preceding depolarization is steeper. c, The rate of depolarization is inversely correlated with the spike threshold in a subset of 20 neurons. The threshold decreases (moves closer to the resting potential) when the rate of depolarization that precedes the spikes increases (gets closer to the maximum rate). d, In most neurons (45 of 52 neurons), the rate of depolarization preceding the onset spike evoked by sound shows higher values than for spontaneous spikes. Error bars indicate SEM. The dashed linewould result if the rate of depolarization were the same for spontaneous and sound induced spikes.
- Fig. 7.
Spike threshold is independent of stimuli.a, ILD curve. b, ITD curve from the same neuron. c, Rate–intensity curves for different stimuli indicated by different symbols. d, Number of spikes versus membrane potential evoked by sound. The response to different combinations of ITD and ILD at different sound levels shows similar trends, indicating that for the same membrane potential, the cell will respond with a similar number of spikes despite differences in stimuli.ABI, Average binaural intensity; SPL, sound pressure level.
