Behavioral plasticity in aneural organisms

Few contemporary psychologists would probably object to the notion that cognitive processes contribute to behavioral plasticity (learning) and are intimately linked to brain function. However, growing evidence suggests that behavioral plasticity is present in organisms lacking neurons (i.e., aneural organisms). This possibility would imply that at least some cognitive processes might have preceded the evolution of nervous systems. Evidence of learning in aneural organisms is reviewed within a mechanistic framework emphasizing four levels of analysis: psychological, neurobiological, neurochemical, and cell-molecular. Learning phenomena ranging from habituation to conditioning have been reported in some aneural organisms, and some key examples are reviewed with attention to evidence of underlying mechanisms. Species comparisons are framed in terms of the central evolutionary concepts of homology and homoplasy. This evidence raises the question of what new behavioral capacities were supported by the evolution of neurons that were not possible before. (PsycInfo Database Record (c) 2025 APA, all rights reserved).