Scientific American: Eight smart limbs plus a big brain add up to a weird and wondrous kind of intelligence
Octopuses and their kin (cuttlefish and squid) stand apart from other invertebrates, having evolved with much larger nervous systems and greater cognitive complexity.
The majority of neurons in an octopus are found in the arms, which can independently taste and touch and also control basic motions without input from the brain.
Octopus brains and vertebrate brains have no common anatomy but support a variety of similar features, including forms of short- and long-term memory, versions of sleep, and the capacities to recognize individual people and explore objects through play.