Limitations of the sensitive period for sexual imprinting: neuroanatomical and behavioral experiments in the zebra finch (Taeniopygia guttata).

In the course of developmental sensitive periods, an animal receives input from the environment which shapes its behaviour and neuronal connectivity. While normally restricted to early development, it has been shown frequently that an extension of the sensitive period to later ages is possible by sensory deprivation or inadequate stimulation. This raises the question whether sensitive periods can be shifted to any age, or whether a time window exists within which sensitive period shifts are possible. We show here for sexual imprinting that such a time window exists, and we also show that the spine density changes during development in brain areas involved in imprinting predict the limits for sensitive period shifts. Based on these results, we speculate about the mechanisms which may underlay the regulation of spine density and thus the imprinting process.