Auditory-evoked action potential activity in MMAN and HVC.

<p>Simultaneous multiunit activity from ipsilateral MMAN and HVC in response to playback of the bird's own song (BOS), the BOS in reverse (REV), and conspecific (CON) song. For both HVC and MMAN, top row, raw data for a single playback of each song; middle row, raster plot of activity to thirty iterations of each song; bottom row, peri-stimulus time histogram (PSTH) of the cumulative response to each song playback. Bin size = 25 ms. The response strength (RS) for each response is given, * indicates a RS that was significantly greater than 0 (one-tailed t-test; p<0.05). For MMAN response to REV, p = 0.06; CON, p = 0.08.</p

GABA inactivation of the area ventral to MMAN resulted in a reduction in auditory responses in HVC.

<p>A, Left, HVC response to ten iterations of BOS before, during, and after GABA application. Right, normalized response to BOS. B. Location of the GABA injection (*). Dye was located ventral to LPS and medial to Area X (outlined by dotted line). The midline is indicated by the line (arrow). Scale bar, 200 µm. M, medial; V, ventral.</p

Comparison of auditory responses and song selectivity in simultaneously recorded multiunit activity in MMAN and HVC.

<p>A. Comparison of the response strength in HVC and MMAN. HVC had a significantly larger RS to BOS than did MMAN (*; paired t-test, p<0.05). The response to REV and CON in HVC and MMAN were not significantly different (REV, p = 0.17; CON, p = 0.47). B. Z-score for auditory-evoked activity in HVC and MMAN. HVC had a significantly higher z-score to BOS than did MMAN (*; paired t-test, BOS, p<0.01). The response in HVC and MMAN to REV and CON were not significantly different (REV, p = 0.20; CON, p = 0.15). C. Comparison of z-scores from simultaneous recorded activity in HVC and mMAN. Black diagonal line is the unity line. D. Both HVC and MMAN were selective for BOS vs REV and BOS vs CON. Selectivity was defined as d′>0.5 (dashed horizontal line). E. HVC was more selective for BOS versus CON than simultaneously recorded MMAN, as many points lie above the unity line than expected at random (p<0.05). The points for BOS versus CON did not lie significantly above the unity line than expected at random (p>0.05). The grey bars demark non-significant d′ values for MMAN and HVC; i.e., −0.5>d′>0.5.</p

Schematic of the feedback loop to HVC through MMAN.

<p>For clarity, anatomical connections are only shown for the right hemisphere. HVC projects to the robust nucleus of the archipallium (RA), which projects to the (DMP). DMP projects bilaterally to MMAN. RA also projects to premotor nuclei that control the syrinx and respiration (PAm and RAm). Abbrev: DMP, dorsomedial nucleus of the posterior thalamus; MMAN, medial magnocellular nucleus of the nidopallium; nXIIts, tracheosyringeal part of the hypoglossal nucleus; PAm, paraambigualis; RAm, retroambigualis.</p

Inactivation of MMAN resulted in little change in HVC auditory responses.

<p>A. Example of auditory evoked activity in MMAN and HVC before (left) and with (right) GABA application to MMAN. Top trace, PSTH of HVC response to ten iterations of BOS playback. Bin size, 25 ms. Middle trace, single, raw example of multiunit activity in HVC. Bottom trace, sonogram of BOS. B. Location of GABA application in MMAN approximated by rhodamine labeling (arrows). LMAN is outlined to the right of the dye (dotted semicircle, *). Scale bar, 200 µm. The dashed vertical line denotes the midline. Dorsal is upward. C. Average response of HVC to BOS presentation before (pre), during (GABA) and after (post) BOS presentation. In two experiments (filled squares) GABA application to MMAN did not produce a significant change in HVC response. In one experiment (open squares) there was a significant decrease in the HVC response to BOS during GABA application compared to pre and post GABA application (ANOVA, p<0.5, Tukey post-hoc). In one bird (open stars) the response to BOS increased throughout the duration of the experiment (pre, GABA, and post were all significantly different than each other; p<0.5, ANOVA, Tukey post-hoc). D. Normalized responses of data shown in C.</p