Neural mechanisms of sexual imprinting

Sexual imprinting is an early learning process by which a young animal acquires information which will help in choosing a sexual partner. It consists of two separate phases, an acquisition phase where features of the social environment are learnt, and a stabilisation phase in which, guided by the previously acquired social information, a preference for a sexual partner is established and stabilised, such that it cannot be altered subsequently. The stabilisation process is short and can be controlled experimentally. This review summarises research on the neural events accompanying consolidation in those brain areas which have previously been identified as important for imprinting. It shows that the period during which consolidation can occur can be shifted only within a certain time window, and demonstrates the fast adjustment of spine densities within the imprinting areas after consolidation has started. It further suggests that long term potentiation (LTP) and long term depression (LTD)-like mechanisms may be involved in this learning process, and that the immediate early genes ZENK and c-fos are expressed within the relevant imprinting areas in the course of consolidation. Evidence is presented for a prominent role of the lateral neostriatum in the imprinting process, and also for the involvement of the hippocampus in this type of early learning.