Fig. 1

Bilateral muscimol infusion in lateral field L lowers performance on both tempo and pitch discrimination tasks. A, B Example song stimuli for tempo (A) and pitch (B) discrimination tasks. Only the stimuli with largest tempo (± 16%) and pitch shifts (± 1/12 octaves) are shown. Inset in B Spectrogram of an example syllable (green boxes) to illustrate pitch shifts (numbers 1 to 5 label corresponding harmonics between the two shifts). C, D Example learning curves for one bird trained on the tempo task (C) and a different bird trained on the pitch task (D). Data are grouped into blocks of 200 trials (~ 3 blocks / day). The lines with different shades of gray (black, dark gray, and light gray) represent 3 different shifts in tempo or pitch with lighter lines representing smaller shifts. The triangles on the x-axis indicate the time of implant surgery. The horizontal bars indicate infusion sessions that occurred on different days (blue: bilateral PBS; red: bilateral muscimol; green: unilateral muscimol). E, F Psychometric curves for different infusion sessions (blue: PBS; red: bilateral muscimol; green: unilateral muscimol; mean ± SEM). *p < 0.05, **p < 0.01, ***p < 0.001, Tukey–Kramer post-hoc test (PBS vs. bilateral muscimol). No significant difference found between PBS and unilateral muscimol condition. G Photomicrographs of auditory forebrain regions in parasagittal sections that show the extent of biotinylated muscimol spread from ~ 0.5 mm lateral, where no biotin staining is visible, to ~ 2 mm lateral, where a dialysis probe was implanted. Top rows: 40 μm sections stained for biotinylated muscimol and adjacent Nissl stained sections. Bottom plot: the intensity of biotin staining as a function of distance from the midline (1 hemisphere from a tempo bird; 8 hemispheres from 4 pitch birds). The thick black line is from the example sections shown above. L: field L; CM: caudal mesopallium. Scale bar = 1 mm