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Extended Data Fig. 7 | Signal shape and onset time of sequence-correlated
HVC neuron activity ref lect within-phrase timing. a, Simulation of calcium
indicator (GCaMP6f) f luorescence corresponding to syllable-locked spike
bursts in HVC PNs. Syllable-locked spike bursts are convolved with the
indicator’s kernel (see Methods) to estimate the expected signal when the
number of spikes per burst is constant (left), ramps up (middle), or ramps down
(right) linearly with the syllable number. The simulation assumes one burst per
syllable in time spacing (x axis) that matches long canary syllables (400–
500ms), medium-length syllables (100 ms) and short syllables (50 ms).
b, Complementing Fig. 3a, average context-sensitive activity in phrases with
long syllables reveals syllable-locked peaks aligned to phrase onsets (left) or
offsets (right, same row order as left) that change in magnitude across the
phrase. c, Signal shape and onset timing have properties of within-phrase
timing codes. Example raw Δf/f 0 signals (y axis, 0.1 marked by vertical bar) of
four ROIs aligned to the onset of specific phrase types (green line). Sonograms
show the repeating syllables. Red lines and blue box plots show the median,
range, and quartiles of the phrase offset timing. The signal shapes resemble the
expected f luorescence of the calcium indicator elicited by syllable-locked
ramping (sketches, top three) or constant activity (bottom). d, Left, barcodes
show the fraction of signal onsets found in the preceding transition, within the
phrase, and in the following transition (T→P→T, see Methods). Rows correspond
to the phrases in Fig. 3a. Right, rows show the average signal state occupancy
estimated from HMMs fitted to the single-trial data used for Fig. 3a. The
resulting traces are time-warped to fixed phrase edges (white lines).
e, Single-trial data from Fig. 3a aligned to phrase onsets (left) and offsets (right)
and averaged in real time. The resulting traces are ordered by peak location
(separately in left and right rasters).