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

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Abstract
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, 1971) 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 conditioned autonomic response.