Heterosynaptic Plasticity: History and Evolution of the Concept in Aplysia and Vertebrates

Invertebrate and vertebrate experimental models, each providing unique advantages for addressing specific questions, offer a multifaceted and multiscale view of plasticity. Integration of the obtained knowledge is crucial for understanding general principles and specific mechanisms of synaptic plasticity. However, this process is hindered by field-specific discrepancies in terminology and concepts. A profound case of such discrepancy is heterosynaptic plasticity, which refers to distinct experimental phenomena and mechanisms and serves different functional roles in invertebrate and vertebrate nervous systems. In Aplysia research, heterosynaptic facilitation originally referred to several phenomena and mechanisms of synaptic plasticity that mediate simple forms of learning. In vertebrate research, heterosynaptic plasticity originally referred to changes at synapses that were not activated during the induction of long-term potentiation in the hippocampus. Ironically, most of the difference between the wordings comes from the meaning attributed to their common part, the heterosynaptic. Here, we consider these differences and discuss how the phenomena and concepts behind the field-specific terminologies are related and can be compared.