Other Minds: The Octopus and the Evolution of Intelligent Life

by Peter Godfrey-Smith

A common octopus (Octopus vulgaris) has about 500 million neurons in its body. That’s a lot by almost any standard. Humans have many more – something like 100 billion – but the octopus is in the same range as various smaller mammals, close to the range of dogs, and cephalopods have much larger nervous systems than all other invertebrates.

an octopus has three hearts, not one. Their hearts pump blood that is blue-green, using copper as the oxygen-carrying molecule instead of the iron which makes our blood red.

Milner and Goodale put together a theory of what’s going on – in us, as well as in special cases like DF’s. They argue that there are two “streams” by which visual information moves through the brain. The ventral stream, which takes a lower path through the brain, is concerned with categorization, recognition, and description of objects. The dorsal stream, which runs above it, closer to the top of the head, is concerned with real-time navigation through space (avoiding obstacles as you walk, getting the letter through the slot). Milner and Goodale argue that our subjective experience of vision, the feel of the visual world, comes only from the ventral stream.

Back in the 1980s, in one of the first modern attempts to explain consciousness, the neuroscientist Bernard Baars introduced the global workspace theory. Baars suggested that we are conscious of the information that has been brought into a centralized “workspace” in the brain. Dehaene adopted and developed this view. A related family of theories claim that we are conscious of whatever information is being fed into working memory, a special kind of memory which holds an immediate store of images, words, and sounds that we can reason with and bring to bear on problems.

Inner speech seems to be an important part of System 2 thinking. It is a way of walking through the consequences of actions, a way to bring reasons to bear against temptation. Gesturing to the careening inner monologues of the novels of James Joyce, Daniel Dennett has called the outcome of this wiring-in of speech a Joycean machine in our heads.

To write a note and read it is to create a reafferent loop. Rather than wanting to perceive only the things that are not due to you – finding the exafferent among the noise of the senses – you want what you read to be entirely due to your previous action. You want the contents of the note to be due to your acts rather than someone else’s meddling, or the natural decay of the notepad.

T]he octopus nervous system contains about 500 million nerve cells, more than four orders of magnitude greater than in other molluscs (garden snails, for example, have around 10,000 neurons) and more than two orders of magnitude more than in advanced insects (cockroach and bee, for example, have around a million neurons), which probably rank next to cephalopods in invertebrate behavioral complexity. The number of neurons in the octopus is well into the range of amphibians such as the frog (~16 million) and small mammals such as the mouse (~50 million) and rat (~100 million), and not much fewer than in the dog (~600 million), cat (~1000 million) and rhesus monkey (~2000 million).”