Structure of Bengalese finch song (A) Example spectrogram (bird 7) depicting an entire song bout with introductory state ‘I’, repeat phrase ‘B’ and individual syllables. (B) Example transition diagram depicting a branchpoint with variable sequencing. Numbers above the arrows denote transition probabilities in percent. (C) Example spectrogram of a chunk. Chunks are defined as highly stereotyped sequences of syllables which only have a single in- and output branch and are condensed into one state in the transition diagram (see Methods). (D) Example spectrogram of a repeat phrase, summarized by capital letter ‘B’ in the transition diagram. The repeating syllable (here, syllable ‘b’) repeats a variable number of times across different instances of the repeat phrase. (E) Schematic showing recurrent pathways projecting onto motor pathway nuclei through lMAN and mMAN. Red: pallial nuclei, blue: thalamic nuclei, green: basal ganglia. Dotted line indicates suspected connection by Kubikova et al. 2007. Abbrev: mMAN: medial magnocellular nucleus of the anterior nidopallium, DMP: dorsomedial nucleus of the posterior thalamus, BG: basal ganglia, DLM: medial portion of the dorsolateral thalamus, lMAN: lateral magnocellular nucleus of the anterior nidopallium, RA: robust nucleus of the arcopallium. (F) Example of a transition diagram. Nodes denote chunk or syllable labels, numbers denote transition probabilities (in percent, % symbol omitted for clarity), d1/d2, g1/g2 denote different states of syllables d and g respectively based on different sequential contexts, capital letters denote repeat phrases. Edges at each node may not sum to 100% because branches smaller than 5% are omitted for clarity.

Transition entropy increased after bilateral mMAN lesions (A) Example spectrogram (bird 3) pre lesion (above) and post lesion (below). ‘I’ denotes introductory state, and ‘fe2’ and ‘ah’ denote chunks, shown as single nodes in the transition diagram. (B) Pre lesion transition diagram, as in 1F. Note that ‘fe2CB’ is also a chunk before the lesions but is shown as three separate nodes in order to align with the post lesion diagram in C. (C) Post lesion transition diagram. Arrows in red mark example nodes with relatively high increase in transition entropy, including the introduction of new branches after mMAN lesions. (D) Total transition entropy for 7 birds before and after mMAN lesions (* p<0.05, n=7, Wilcoxon signed-rank test). Example bird from A-C is shown as darker line.

Chunks became more variable after bilateral mMAN lesions. (A) Example spectrogram (bird 2) before and after bilateral mMAN lesions. Atypical chunk sequences are highlighted in red. (B,C) Transitions following the first ‘c’ of the ‘ccllfk’ chunk from (A) before and after mMAN lesions. Different column colors represent different syllables. (D) Chunk consistency before and after bilateral mMAN lesions (** p<0.01, n=23, Wilcoxon signed rank test). Example bird is shown as darker line.

The number of syllables per repeat phrase (repeat number) became more variable after bilateral mMAN lesions. (A) Example spectrogram (bird 6) highlighting one repeating syllable before (blue) and after (red) mMAN lesions. (B) Repeat numbers for two additional example birds before (blue) and after (red) mMAN lesions. (C) Average repeat numbers before and after mMAN lesions for all repeat phrases. (D) Coefficient of variation for distribution of repeat numbers before and after mMAN lesions for all repeat phrases. Example birds from B are shown as darker lines.

Increase in transition entropy after mMAN lesions remains consistent over several days. Transition entropy did not change in a consistent way after recovery from the lesion for the followed time period. Numbers near the datapoints indicate number of song bouts recorded and analyzed for that day.

Syllable types are preserved after mMAN lesions. Average spectrograms of 200 instances of all syllable types for all birds before and after mMAN lesions. Letters over the spectrograms indicate syllable labels.

Example image of calcitonin gene-related peptide (CGRP)-stained frontal section of bird 5. CGRP labels cells in both lMAN (seen in black to the left of the lesion) and mMAN (completely destroyed).

Change in transition entropy for branchpoints (A) Transition entropy increased for branchpoints after mMAN lesions. (B) Branchpoints with low history dependence before mMAN lesions tended to show a higher change in transition entropy.

Change in transition entropy for transitions within chunks vs. branch points (A) Duration of gaps within chunks before mMAN lesions was weakly correlated with entropy change at the corresponding transition. (B) Change in transition entropy was approximately equal for transitions within chunks and at branchpoints.