EA - What might decorticate rats tell us about the distribution of consciousness? by Derek Shiller

Link to original articleWelcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: What might decorticate rats tell us about the distribution of consciousness?, published by Derek Shiller on July 20, 2022 on The Effective Altruism Forum. Summary: The cortex is generally thought to be the seat of consciousness in human beings. A body of literature indicates that the cortex is not integral to many intuitively conscious behaviors in rats. This suggests that either rats don’t rely conscious experiences to guide their behavior in the way we do, or else that consciousness depends on distinct mechanisms in humans and rats. All told, we should think this body of literature is evidence against the hypothesis that mammals are generally conscious and non-mammalian vertebrates are not. Epistemic status: I’m not an expert in much of the material surveyed here. Particularly the function of brain regions and lesioning studies in animals. These issues are important and my impression is that very few people have the comprehensive expertise to think well about these things. Caveat: I’m wary of the decortication studies because they seem so out of line with what I would expect given the prevailing opinions and they are discussed very little in contemporary neuroscience. That said, I have a hard time seeing how they could be grossly inaccurate and I’ve never seen anyone challenge them. Main ideas are bolded. Intro All vertebrate brains follow a similar plan in rough outline. At the highest level, they are generally divided into three parts: the fore, the mid, and hindbrain. In humans and other mammals, the forebrain consists in the cerebral cortex and several smaller structures. The mammalian cerebral cortex houses a number of specialized sensory processors and muscle controls along with general association regions of less specific purpose. In humans and other apes, the cerebral cortex is also widely believed to be largely responsible for generating our conscious experiences. While structures in the mid or hindbrain control aspects of body regulation and arousal, our experiences are thought to be produced in the cortex. We have successfully mapped out sensory regions and have some understanding of how their activity correlates with conscious contents. Damage to regions of the cortex radically alters cognition and affects conscious experiences in a variety of ways. Moreover, severe damage to the human cerebral cortex destroys all signs of awareness and intentional activity. A human without a cerebral cortex is, for the most part, a living body with no mind. Primates differ from many other animals in the central role their cortex plays in their cognitive lives. The effects of cortical loss in rats has been studied in depth in a series of neuroscientific experiments (Whishaw 1990)[1], carried out mostly in the 1960s-80s. The results of these studies are striking. The behavior of decorticate rats is remarkably unaffected by extensive damage or removal of their cerebral cortex. The afflicted rats are impaired by the loss of cortical tissue, but not nearly as much as one would expect. The obvious behavioral implications to decortication noted by experimenters are extremely benign relative to what I would have antecedently expected. They include: A laundry list of small idiosyncratic changes, e.g.: Impaired muscle control over the tongue and jaws Postural changes while grooming Increased use of forepaws during swimming Various social changes Notably, inferior maternal care Difficulty with some complex cognitive tasks Inability to reason abstractly about locations Absence of food hoarding behavior I suspect that there are a lot of complicated ways that decortication does change behavior, but which require subtle experimental designs to detect. Surely, the cortex must do a lot of important things to be worth its metabolic cost. However, losing the cortex does not radically aff...