FIGURES
journal-pbio-0060250-g002

doi:10.1371/journal.pbio.0060250.g002

Figure 2.HVC Stimulation Leads to Song Distortions at the Syllable and the Motif Levels

(A) Spectrogram of an adult male zebra finch song bout (top) with song motifs indicated by horizontal arrows. Below are a zoom into a normal (nonstimulated) song motif and examples of syllable-level stimulation (Stim) effects (truncation and distortion, indicated by asterisks), and examples of motif-level effects (stopping and restart, with the restarting point indicated by an asterisk).

(B) Top: spectrogram of the song motif in (A). Bottom: sound-amplitude stack plot depicting stimulation effects observed over the course of a day. Trials are ordered by stimulation time, marked by white dots. The top 200 traces depict nonstimulated catch trials, revealing the high stereotypy of song motifs. The pink arrows indicate corresponding stimulation trials in (A). Stimulation effects display a contiguity, as revealed for example by nearby stimulation times that lead to persistent syllable truncations and early motif restarts (top pink arrow).

(C) Effects on sound amplitudes started 20 ms after HVC stimulation and peaked after about 50 ms. Shown is the histogram of time bins with amplitude effects as function of latency to stimulation, normalized to the peak and averaged over stimulation sites (average over n = 20 HVC stimulation sites in 10 birds). On average, the peak effectiveness occurred after about 50 ms, well within the EE window.

(D) An example in which HVC stimulation over a broad temporal range leads to identical syllable truncation times. In the unperturbed spectrogram (catch trial, top), we marked the normal offset time of a selected syllable with the magenta vertical dashed line. Below are song spectrograms with identical syllable truncation times (pink vertical dotted lines) for both early and late stimulation (stimulation times are marked by white vertical lines). The sound-amplitude stack plot (between the stimulation examples) reveals that all syllable truncations (pink dots, shown only for intermediate stimulation times) are vertically aligned, irrespective of stimulation time (white ramp dots, left). Note also that syllable truncations were followed by an unusual syllable that was never observed at this location during catch trials. The onsets of this appended syllable are marked by white vertical dashed lines in the “early” and “late” stimulation examples and by the cloud of white dots in the stack plot (shown for intermediate stimulation times). An F-test revealed that the onset times of this appended syllable had the same variance when measured relative to song detection time and relative to stimulation time (p = 0.1). Hence, the timing of this syllable was fixed neither to stimulation time nor to song time.

(E) A stimulation example in a different bird in which syllable truncations (pink dots) tended to occur during a particular note rather than at a fixed time lag after stimulation. Same legend as in (D).

(F) LEs increased with stimulation current. The LE curve associated with the stack plot in (B) is depicted by the blue curve (150 μA, single pulse). LE curves for higher and lower stimulation currents are also shown (brown and black curves). With increasing current, more stimulation times lead to LEs. The lower panel illustrates the computation of effect curves in this bird. The red line indicates stimulation time; black rasters indicate 3.9-ms time bins in which stimulation-related sound amplitudes were significantly different from baseline; and the green lines delimit the time windows in which EEs and LEs were read out. Note that the stack plot in (F) is not perfectly (horizontally) aligned with that in (B) because of randomness of stimulation times (wiggly white line in [B]).

From: Rapid Interhemispheric Switching during Vocal Production in a Songbird Wang CZH, Herbst JA, Keller GB, Hahnloser RHR PLoS Biology Vol. 6, No. 10, e250 doi:10.1371/journal.pbio.0060250