Avian archistriatal control of fear-motivated behavior and adrenocortical function

Bilateral section of the efferent pathway (tractus occipitomesencephalicus) from the archistriatum of the duck depresses fear-motivated responses as measured by (a) latency to escape in a runway test; (b) latency to approach and drink in the experimenter's presence following water deprivation, and (c) number of agonistic responses directed to an object introduced into the home cage. Sectioning this pathway also raises plasma corticosteroid levels in both adult mallards and newly hatched chickens. Plasma corticosteroid levels were negatively correlated with latency to approach and drink in controls. Experimental reduction of the neutral output of the mallard archistriatum produces an animal that resembles the adult domesticated duck in its basal plasma corticosteroid level and in its avoidance behavior, suggesting that selection for reduced archistriatal activity occurs during domestication.