The dorsocaudal neostriatum of the domestic chick: a structure serving higher associative functions

The dorsocaudal neostriatal (dNC) complex consists of at least three functionally distinct subregions and is part of an 'imprinting' pathway, which interconnects several forebrain regions that are known to be involved in juvenile learning. Based on its anatomical features, at least one subregion of the dNC complex, the neostriatum dorsocaudale (Ndc) may be considered as the equivalent of the mammalian polysensory association cortices. Several lines of evidence point to a role for this forebrain region in learning and memory formation. After auditory or visual imprinting changes of stimulus-evoked metabolic activities and of synaptic densities have been measured in the Ndc. Pharmacological behavioral studies revealed that the activation of NMDA receptors plays a critical role during this learning process and that NMDA receptor activation is required for the associated metabolic and synaptic changes. In addition to glutamatergic afferents, anatomical studies revealed a massive input from monoaminergic and peptidergic pathways into the dNC complex, suggesting a modulatory role for these systems during imprinting. The results presented here together with data from other avian species support the view that the dNc complex, and in particular the Ndc, plays an important role in juvenile and adult learning.