The spatial distribution of neuronal responses to autogenous song (AS) was investigated in the HVc of urethan-anesthetized adult male zebra finches (Taeniopygia guttata). In seven birds, penetrations covered the entire mediolateral, rostrocaudal, or dorsoventral extents of HVc. In an eighth, control birth penetrations were made near to but outside of HVc. Reconstruction of recording sites from histological material indicated a good correspondence between sites that exhibited stronger responses to AS than to tone or noise bursts, and sites that were within HVc. 2. Within each experimental bird but not in the control, multiple-unit responses to AS were similar across the entire spatial extent of HVc (up to 1.3 mm). For each experimental bird, the strongest responses occurred within a narrow range of times. The middle of this range of times is called the time of maximum synchronization (TMS). Across birds, 34-75% of recording sites exhibited the same TMS. With the use of a criterion of > 33% of sites exhibiting their strongest responses at the TMS, the temporal scatter around the TMS varied between 6 and 138 ms across individuals. In six of the seven experimental birds, the position of the TMS was not affected by changing the window of integration from 10 to 150 ms. In two experimental birds, short windows of integration tended to emphasize beginning portions of the song. In one case this effect was sufficiently strong to change the TMS for short windows of integration. 3. Each TMS was associated with a syllable of maximum synchronization (SMS). The positions of the SMS varied considerably across birds. In four birds the SMS was one of the syllables of the first motif (a motif is a temporal sequence of syllables that can be repeated > or = 1 times to form a song), in two birds the SMS was the introductory note of song, and in one bird the SMS was the second syllable of the last (3rd) motif. Syllables of the same type as the SMS but occurring in other motifs typically elicited much weaker responses, in many cases weaker than other syllables in those motifs. Syllables that elicited strong responses in non-SMS motifs did not necessarily elicit strong responses in the SMS motif, even if they preceded the SMS. There were no apparent acoustical features of the SMS or the preceding syllable that could account for the global synchronous response to song.(ABSTRACT TRUNCATED AT 400 WORDS)
