The interanimal transfer phenomenon: A review

The phenomenon described as interanimal transfer of learned responses from trained donor animals to untrained recipient animals by means of brain extracts has been regarded as problematic by many investigators and has generated extensive literature. Among major issues have been the reproducibility of the phenomenon and the viability of a learning interpretation of the recipients' behavior. The learning interpretation, if correct, makes direct experimental approaches to brain-behavior relationships feasible in the context of learning and memory. The review led to a number of conclusions with respect to the issues and evidence. Reproducibility has become less of a problem but has not been eliminated. Several species have been used successfully, and the effect has been reported over a wide range of tasks. The transfer effect, considered at a behavioral level of analysis, exhibits an empirical relationship with donor training and learning. While there is also evidence of a transfer of a nonspecific arousal factor, it cannot account for all of the data. Given the relatively crude extracts used in many cases, a 2-factor explanation of transfer appears most likely, in which an arousal transfer occurs under one set of conditions, and a learning transfer under others. The behavioral challenge resulting from this notion is the clear separation of the 2 effects. Biological and chemical mechanisms of the effect have not been widely researched, possibly due to a lack of formal consensus about what the transfer effect represents and thus its significance. (3 p ref)