2014 : WHAT SCIENTIFIC IDEA IS READY FOR RETIREMENT?

We humans have had a tough time coping with our unremarkable place in the grand scheme of things. First Copernicus trashed our belief that we live at the centre of the universe, followed shortly thereafter by Herschel and co. who suggested that our sun was not at the centre of it either; then Darwin came along and showed that according to our biological heritage, we are just another animal. But we have clung on for dear life to one remaining belief about our specialness; that we, and we alone, have conscious minds. It is time to retire, or indeed euthanize and cremate, this anthropocentric pomposity.

Descartes thought of animals as mindless automata, and vivisection without anesthetic was common among early medical researchers. Throughout much of the 20^th century, psychologists believed that animals—while clearly resembling humans in their neuroanatomy—perform their activities essentially unthinkingly, a viewpoint that reached its zenith (or perhaps, my preferred word, nadir) in Behaviorism, the psychological doctrine that rejects inner mental states like plans and purposes as unable to be studied, or—in the radical version—as not even existing. The undeniable fact that humans have inner mental states and purposes was attributed to our special psychological status: we have language, and therefore we are different. Animals remain essentially Cartesian automata though.

Many of our scientific experiments have validated this view. Rats in a skinner box (named after the most radical Behaviorist of all, BF Skinner) do indeed appear to act mindlessly—they press the levers over and over again, they seem slow to learn, slow to adapt to new contingencies, they don't really seem to think about what they are doing. Furthermore, in further testament to its mindlessness, quite large regions of the brain can be damaged without affecting performance. Rats in a maze seem similarly clueless—they take a long time to learn (weeks to months sometimes) and a long time to adapt to change. Clearly, rats and other animals are stupid—and more than that, they are mindless.

Fond though I am of rats, I would not wish to defend their intelligence. But the assumption that they do not have inner mental states needs examining. Behaviorism arose from the argument of parsimony (Occam's razor)—why postulate mental states in animals when their behavior can be explained in simpler ways? The success of Behaviorism arose in part from the fact that the kinds of behaviors studied back then could, indeed, be explained by operation of mindless, automatic processes. It does not take deep reflection to press a lever in a skinner box any more than it does to key in your PIN. But in the mid-20th century, a development occurred that began to overturn the view that all behavior is mindless. This development was single neuron recording, the ability to follow the activity of individual brain cells—the little cogs and sprockets that make up the workings of the actual brain. Using this technique, behavioral electrophysiologists have been able to actually see, for themselves, the operation of inner mental processes in animals.

The most striking discovery along these lines has been the place cells, neurons in the hippocampus, a small but vitally important structure located deep in the temporal lobes. Place cells are (we now know) key components of an internal representation of the environment—often called the cognitive map—which forms when an animal explores a new place, and which reactivates when the animal re-enters that place. Single neuron recording shows us that this map forms spontaneously, in the absence of reward and independently of the animal's behavior. When an animal is choosing between alternative routes to a goal, place cells representing the alternative possibilities become spontaneously active even though the animal has not gone there yet—as if the animal is thinking about the choices. Place cells certainly seem to be an internal representation: furthermore, we humans have them too, and human place cells reactivate when people think about places.

Place cells may well be an internal representation of the kind eschewed by behaviorists, but does this mean, though, that rats and other animals have minds? Not necessarily… place cells could still be part of an automatic and unconscious representation system. Our own ability to conjure up remembered or imagined images "in our mind's eye" to use for recollection or planning might still be special. This seems unlikely though, doesn't it? Mindlessness would only be a parsimonious conjecture if we didn't know about our own minds. But we do… and we know that we are extraordinarily like animals in every respect, right down to the place cells. To suppose that the ability to mentally represent the outside world sprang into existence, fully formed, in the evolutionary transition (if the concept of "transition" even makes sense) between animals and humans seems improbable at best, deeply arrogant at worst. When we look into the animal brain we see the same things we see in our own brains. Of course we do, because we are just animals after all. It is time to admit yet again that we are not all that special. If we have minds, creatures with brains very like ours probably do too. Unravelling the mechanisms of these minds will be the great challenge for the coming decades.