Involvement of the avian amygdalar homologue (archistriatum posterior and mediale) in defensively conditioned heart rate change.

Archistriatal involvement in visually conditioned heart rate change (established by pairing light and foot-shock) was studied in 198 pigeons by evaluating conditioning performance following lesions of different archistriatal subdivisions or interruption of their subtelencephalic projections. Lesions of the anterior-intermedium archistriatum or interruption of its descending projection (tractus occipitomesencephalicus) had no effect on conditioned response development. In contrast, destruction of the posterior-mediale region or interruption of its descending projection (tractus occipitomesencephalicus, pars hypothalami) produced profound conditioning deficits. The findings are entirely consistent with a recent anatomical analysis (Zeier and Karten, '71) suggesting that only the posterior-mediale archistriatum constitutes the avian amygdalar homologue. It is concluded that the integrity of the posterior-mediale region and its projection to the hypothalamus via the tractus occipitomesencephalicus, pars hypothalami are essential for establishing visually conditioned heart rate change in a defensive conditioning paradigm, and these findings are discussed in the context of structures previously implicated in mediating this conditioning autonomic response.