Filial imprinting in domestic chicks is associated with spine pruning in the associative area, dorsocaudal neostriatum

Juvenile emotionally modulated learning events are fundamental for the norm al development of socio-emotional competence and intellectual capabilities. Filial imprinting in the domestic chick provides a suitable model to inves tigate the neural mechanisms underlying such juvenile learning events. The forebrain area dorsocaudal neostriatum (Ndc), a multimodal integration area and presumed equivalent to mammalian parietotemporal association cortices, has been shown to be critically involved in this learning process. We inve stigated whether filial imprinting is associated with changes of synaptic c onnectivity in the Ndc. Quantitative measurements of spine densities of a l arge neuron type in the Ndc revealed a massive pruning of spine synapses af ter filial imprinting. Compared with 7-day-old naive control chicks, imprin ted chicks displayed significantly lower spine frequencies on all dendritic segments. Since the average length of the dendritic segments did not chang e during imprinting, these results can be interpreted as a reduction of the absolute number of spine synapses on this neuron type. In a control region , the primary sensory forebrain area ectostriatum, spine density and dendri tic length remained unchanged. These results indicate that synaptic pruning may represent a mechanism of selective synaptic reorganization in higher a ssociative forebrain areas as a fundamental feature of juvenile learning ev ents.