Reading David Peña-Guzmán’s When Animals Dream for New Scientist, 17 August 2022

Heidi the octopus is dreaming. As she sleeps, her skin changes from smooth and white to flashing yellow and orange, to deepest purple, to a series of light greys and yellows, criss-crossed by ridges and spiky horns. Heidi’s human carer David Scheel has seen this pattern before in waking octopuses: Heidi, he says, is dreaming of catching and eating a crab.

The story of Heidi’s dream, screened in 2019 in the documentary “Octopuses: Making Contact”, provides the starting point for When Animals Dream, an exploration of non-human imaginations by David Pena-Guzman, a philosopher at San Francisco State University.

The Roman philosopher-poet Lucretius thought animals dreamt. So did Charles Darwin. The idea only lost its respectability for about a century, roughly between 1880 to 1980, when the reflex was king and behaviourism ruled the psychology laboratory.

In the classical conditioning developed by Ivan Pavlov, it is possible to argue that your trained salivation to the sound of a bell is “just a reflex”. But later studies in this mould never really banished the interior, imaginative lives of animals. These later studies relied on a different kind of conditioning, called “operant conditioning”, in which you behave in a certain way before you receive a reward or avoid a punishment. The experimenter can claim all they want that the trained rat is “conditioned”; still, that rat running through its maze is acting for all the world as though it expects something.

In fact, there’s no “as though” about it. Pena-Guzman, in a book rich in laboratory and experimental detail, describes how rats, during their exploration of a maze, will dream up imaginary mazes, and imaginary rewards — all as revealed by distinctive activity in their hippocampuses.

Clinical proofs that animals have imaginations are intriguing enough, but what really dragged the study of animal dreaming back into the light was our better understanding of how humans dream.

From the 1950s to the 1970s we were constantly being assured that our dreams were mere random activity in the pons (the part of the brainstem that connects the medulla to the midbrain). But we’ve since learned that dreaming involves many more brain areas, including the parietal lobes (involved in the representation of physical spaces) and frontal lobes (responsible among other things for emotional regulation).

At this point, the sight of a dog dreaming of chasing a ball became altogether too provocative to discount. The dog’s movements while dreaming mirror its waking behaviours too closely for us to say that they lack any significance.

Which animals dream? Pena-Guzman’s list is too long to quote in its entirety. There are mice, dogs and platypuses, beluga whales and ostriches, penguins, chameleons and iguanas, cuttlefish and octopuses — “the jury is still out on crocodiles and turtles.”

The brain structures of these animals may be nothing like our own; nonetheless, studies of sleeping brains throw up startling commonalities, suggesting, perhaps, that dreaming is a talent to which many different branches of the evolutionary tree have converged.

Pena-Guzman poses big questions. When did dreaming first emerge and why? By what paths did it find its way into so many branches of the evolutionary tree? And — surely the biggest question of all — what are we do with this information?

Pena-Guzman says dreams are morally significant “because they reveal animals to be both carriers and sources of moral value, which is to say, beings who matter and for whom things matter.”

In short, dreams imply the existence of a self. And whether or not that self can think rationally, act voluntarily, or produce linguistic reports, just like a human, is neither here nor there. The fact is, animals that dream “have a phenomenally charged experience of the world… they sense, feel and perceive.”

Starting from the unlikely-sounding assertion that Heidi the octopus dreams of fresh crab suppers, Pena-Guzman assembles a short, powerful, closely argued and hugely well evidenced case for animal personhood. This book will change minds.