Heterosynaptic Plasticity: History and Evolution of the Concept in <i>Aplysia</i> 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 <i>heterosynaptic plasticity</i>, which refers to distinct experimental phenomena and mechanisms and serves different functional roles in invertebrate and vertebrate nervous systems. In <i>Aplysia</i> research, <i>heterosynaptic facilitation</i> originally referred to several phenomena and mechanisms of synaptic plasticity that mediate simple forms of learning. In vertebrate research, <i>heterosynaptic plasticity</i> 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 <i>heterosynaptic</i>. Here, we consider these differences and discuss how the phenomena and concepts behind the field-specific terminologies are related and can be compared.