Invertebrate sentience: A review of the neuroscientific literature

Abstract

Invertebrates comprise 99% of all animal species and the vast majority of individual animals, yet research on their sentience is limited. This review examines neuroscientific evidence relevant to invertebrate sentience, focusing on neuron number, specialized brain structures, and degree of centralization. While neuron quantity alone does not predict cognitive capacity, functional organization enabled by sufficient neuron numbers is crucial. The presence of a cortex-like structure is no longer considered a prerequisite for sentience, opening possibilities for consciousness in invertebrates like octopuses. The sufficiency of midbrain-like structures for consciousness remains debated. Centralization of information processing, though generally higher in vertebrates, varies significantly across invertebrates. Further research is needed to determine the relevant criteria for invertebrate sentience, assess different invertebrate nervous systems against these criteria, and determine the practical consequences of invertebrate sentience for their welfare. – AI-generated abstract.