Birds diverged from mammals approximately 300
million years ago. The avian and mammalian telencephalon
followed a pattern of convergent evolution, with
similar solutions to functional brain organization.
Here, we review the extensive literature on the
various types of plasticity in the avian brain. Data
collected with behavioral, lesion and electrophysiological
techniques are discussed, as well as pharmacological
and gene-expression studies, revealing the fine
structure of molecular cascades at the basis of functional plasticity in a broad range of processes. Passive avoidance learning (onetrial-
learning following experience of an aversive-tasting substance) and filial
imprinting (the peculiar phenomenon occurring in precocial species whose
newly hatched chicks become socially bonded to the first salient object
encountered) will be discussed as examples of neuronal and behavioral
plasticity. Brain asymmetries, often reported in these studies, will be also
reviewed. Another example of avian brain plasticity considered is the
difference in hippocampal/telencephalon volume ratio among scatter-hoarding
and non-storing birds. Species relying on spatial memory to relocate their
caches (hiding locations) have an enlarged hippocampus due to either
seasonal pressures or different habitat demands stimulating neuronal
recruitment. Plasticity associated with song production and perception in
telencephalic nuclei in songbirds, and with spatial localization of sounds in the
barn owl is also considered. Birds are amongst the vertebrates that display the
most sophisticated and flexible learning abilities in the animal kingdom. Not
surprisingly, in birds environment plays a crucial role on neuronal network
plasticity, with experience-dependent changes acting at both structural and
functional levels during ontogenesis. Overall, the study of plasticity in the
diverse avian models proved to be a valuable tool for the understanding of
brain mechanisms per se but also their evolution in the context of special
ecological constraints, two mandatory steps in order to understand
mammalian brains and this may be an useful aspect in the therapeutic field.
