The Neurophysiological Basis of Learning and Memory in Advanced Invertebrates. The Octopus and the Cuttlefish.

Cephalopod mollusks such as octopus, cuttlefish, and squid (coleoids) are of special interest for studying the evolution and function of learning and memory mechanisms at the system level. They are believed to have the most advanced cognitive behaviors of all invertebrates, rivaling the abilities of many vertebrates. The phylum Mollusca shows the most diversified range of behavioral complexity among the invertebrates, with behavioral complexity correlating roughly with the size of the nervous system (a few thousand vs. half a billion neurons) and its morphological organization (centralized vs. distributed). The mollusks therefore provide an excellent opportunity for assessing conservation and convergent processes in the evolution and development of learning and memory systems subserving complex behaviors. The pioneering work of J. Z. Young, M. J. Wells, and colleagues confirmed that a specific structure in the brain of the modern cephalopods, the vertical lobe, is involved in their highly sophisticated behaviors. This chapter summarizes recent neurophysiological research in the octopus and cuttlefish vertical lobe system that, for the first time, allows a functional and computational approach to the evolution of learning and memory systems.