Lesions Involving Medial Anterior Forebrain Pathway Circuitry Destabilize Phrase Timing in Adult Canary Song
Year: 2026
Type: preprint
Abstract: Basal ganglia-thalamocortical circuits are essential for learning complex motor sequences, yet how they control flexible motor behavior remains poorly understood. The homologous songbird Anterior Forebrain Pathway (AFP) drives song motor learning. Early lesion studies showed no effect on adult song, so the AFP was thought to be unnecessary for adult song performance. Recent evidence shows that the AFP influences song syntax in some species, revising this perspective. We revisit this question in adult canaries by performing bilateral excitotoxic lesions targeting the AFP's lateral and medial subdivisions. To measure behavioral changes, we developed a high-throughput song-annotation pipeline that adds a supervised classifier to the self-supervised TweetyBERT model. This removed the memory bottleneck of UMAP clustering, enabling phrase-level analysis across thousands of songs per bird. We find that lesions involving the medial AFP produce stuttering-like behavior, defined here as prolonged, variable syllable repetition before transitions, which significantly increases phrase-duration variability. This effect appeared only in birds with medial and lateral AFP lesions, not in birds with lateral-only lesions. This increased variability persisted throughout the post-lesion recording period and was accompanied by small changes in syllable acoustic structure. Our results implicate the medial AFP in the ongoing control of phrase duration in adult canary song, challenging the view that the AFP is dispensable once song is learned. These findings position the medial AFP as a tractable model for understanding how basal ganglia and cortical dynamics maintain complex learned motor sequences. Significance Statement: Basal ganglia-thalamocortical circuits are critical for learning complex motor sequences, but their role in performing learned behaviors remains unclear. We found that in adult male canaries, lesions involving the medial and lateral portions of the songbird Anterior Forebrain Pathway (AFP) resulted in an abnormal stuttering-like behavior. We did not detect comparable changes after lateral-only lesions, implicating circuitry involving the medial pathway, although we cannot isolate its independent contribution. These findings challenge the view that the AFP becomes unnecessary once canary song is learned or produced during the more stable breeding-season song, and offer a model for studying basal ganglia contributions to learned motor sequencing. We also develop a scalable annotation pipeline enabling analysis of thousands of songs per bird.
Institution: University of Oregon
Language: English
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7168178279