Fig 1.
Neural response analyses in the time and frequency domains.
Examples of spike responses (raster plots; left) of ICC neurons to tones at the characteristic frequency (CF), respective PSTHs taken 30 dB above threshold at CF (middle), and responses (the number of spikes of three responses per frequency-intensity dyad) defining the excitatory frequency response area with the CF indicated (right). Solid horizontal lines below the x-axes (left, middle) indicate tone duration. The binwidth of the PSTHs is 2 ms. Examples of different temporal response patterns are shown. a: tonic; b: phasic-tonic; c: pauser; d: long-latency; e, f: phasic. Neurons in a–e have shapes of frequency-response areas of class I, the neuron in f of class III.
Fig 2.
Analysis of the precision of tone-onset response latency.
For every neuron, the first-spike latencies of the 9 responses framed by the red box were measured. These responses always concerned the CF- tone and the next lower and higher frequencies at tone levels 30, 35 and 40 dB above CF threshold (arrows). The excitatory frequency response area (example shows a class II neuron) is defined by the vertical dashes (number of spikes to a single tone burst).
Fig 3.
Examples of spike responses (raster plots) of ICC neurons to tones at the characteristic frequency.
Panels a–g show constant patterns (no change of pattern with tone level), panels h–l show variable patterns. The type of pattern is indicated in each panel. Solid horizontal lines below the x-axes indicate tone duration.
Fig 4.
Percentages of neurons in the three classes of FRAs (class I–III) with constant (red) or variable (dark green) temporal response patterns.
Constant and variable refers to CF tones of at least 30 dB above response threshold. N = numbers of neurons in the respective FRA classes.
Fig 5.
Percentages of neurons with the indicated temporal response patterns at 30 dB above CF-tone threshold.
Distributions are shown separately for the neurons in the three classes of FRAs (а: class I; b: class II; c: class III).
Table 1.
Tone-response latencies at CF at 30 dB above CF threshold of neurons in the different classes of FRAs and of different temporal response patterns.
Fig 6.
Percentages of neurons (N = 50) which changed their temporal response patterns depending on the tone level at CF.
Of the 50 neurons, 48 had FRAs of classes I and II. Three ranges of tone levels above CF threshold are indicated: 10–20 dB (blue); 30–40 dB (red), 60–80 dB (black).
Fig 7.
Relationship between average first-spike latencies of the neurons in the three classes and the average widths of their FRAs (expressed as Q30 or Q40 values).
The statistically significant linear regressions (see equations, r and p values) show that, on a global scale, latencies increase with sharpening of excitatory frequency tuning (increase of Q30 and Q40).
Fig 8.
Distribution of the number of neurons with various first-spike latencies in response to CF tones at 30 dB above threshold.
Latency distributions are shown separately for neurons of FRA classes I (a), II (b), III (c), and for all 135 studied neurons (d).
Fig 9.
Temporal response patterns in the whole FRAs of the neurons.
(a) Percentages of neurons in the three classes of FRAs (class I–III) with constant (red) or variable (dark green) temporal response patterns; (b) the distribution of 51 neurons with constant response patterns in different temporal response types; (c)–(e) percentages of neurons in a given FRA class (c: class I, d: class II, e: class III) with constant response patterns of the indicated types.
Fig 10.
Division of the excitatory frequency response area of ICC neurons in core (pink) and periphery (blue).
For definition of core and periphery, see text.
Fig 11.
Numbers of neurons with different ranges of change of response latency within their FRAs.
Ranges of latency change are with reference to response latency to CF tones at 30 dB above threshold. (a) Number of neurons with the indicated minor latency changes (from -6-7 ms up to 6–7 ms) in the core of their FRAs. (b) Number of neurons with the indicated latency changes in their whole FRAs. Latency changes > +/-7 ms occurred in neurons with long-latency responses.
Table 2.
Response latencies (ms) were averaged from neurons with constant (+/-1 ms) latencies in the core of their FRAs and plotted separately for the neurons in the 3 classes of FRAs.
Table 3.
Distribution of neurons with different latency variation (Fig 11B) in the 3 classes of FRAs.
Fig 12.
Latency jitter of individual neurons.
Plotted are the means (with standard deviations) of the latency jitter of individual neurons with the indicated response patterns from the three classes of FRAs (black: class I, blue: class II, red: class III). The left y-axis refers to short-latency responses, the right y-axis to long-latency responses. Latency jitter equals the standard deviations of the tone-response latencies calculated from the 9 responses marked (red frame) in Fig 2. For further explanations, see text. Statistically significant differences between the means are indicated below the mean values, significant differences between the standard deviations above the mean values. * p < 0.05; ** p < 0.01.