If you think the anatomical perspective is messy, then put on your wet-weather gear as we approach physiology. From the physiological (= functional) perspective, the brain is what it does. The problem is that the brain, this anterior ganglion, “does” or participates in nearly every function of a vertebrate. Muscle contraction? Absolutely! Heart rate? Yes. Growth and development? Yes, even that, given the brain’s involvement in hormonal regulation.
With all this brain-mediated physiology going on, it’s extremely useful to try to focus on a single function. Let’s go back to intelligence. Problem: we can’t even agree on a definition. We’ve skimmed through the Turing-versus-Searle debate—that is just one axis of the pool of arguments. Even if we stick with skills-based definitions, we fight over what abilities indicate intelligence. Howard Gardner, professor of cognition and education at Harvard’s Graduate School of Education, famously framed “multiple intelligences” for humans and, even though he has no fixed definition of intelligence, identified eight domain-specific types: spatial, linguistic, logical-mathematical, bodily-kinesthetic, musical, interpersonal, intrapersonal, and naturalistic.[80] Of course, Gardner’s approach gets hammered too. So the paradox is this: how can we study a “thing” if we are all studying different things?
This is where neuroscience really shows its powerful Kung Fu. See, grumpy students of mine, I actually agree with you that by starting with the basics of nervous systems, we create an empirical and materialistic foundation, a molecule 
cell region body chain of causal understanding.[81] However, this understanding only takes us so far, at the moment, and then we are left holding the bag of subjective first-person and other-minds experience to intuit an understanding of our human intelligence. The empirical promise, articulated cogently by Patricia and Paul Churchland, professors of philosophy at the University of California at San Diego, is that our burgeoning neuroscientific understanding is creating a new and neuroscientifically based psychology.[82] Another important build-it-up-from-neurofundamentals approach is that of Jeff Hawkins, founder of Palm Computing and Handspring, who has demonstrated that the anatomy of the human cortex reflects the physiology of two fundamental pieces of intelligence: memory and the ability to predict.[83]
By carefully reviewing cortical anatomy and physiology, Hawkins has shown that the two are conjoined and inseparable. As Stephen Wainwright and Steven Vogel, cofounders of the field that we now recognize as comparative biomechanics, wrote in one of their early lab manuals, “Structure without function is a corpse; function sans structure is a ghost.”[84]
Speaking of ghosts, one kind of confusion about the difference between a brain and a body stems from the implicit substance dualism that permeates our human cultures. Substance dualism, formulated carefully by René Descartes, claims that the mind is made of stuff that is different from the physical stuff that makes up bodies. Consider that for many people, a “mind” is equivalent to or created by a “brain.” If, by intuition or religion, you believe that minds are made of a mysterious and nonmaterial substance, existing in some other dimension or plane after we die, then our brains must be of some special nonbody substance or quality too or possess the ability, as Descartes suggested, to interact with the nonphysical realm. Meanwhile, bodies, fashioned from clay, are earthly containers that are secular, ephemeral. The reasoning and predictions of substance dualism, however, have been refuted repeatedly.[85] We proceed knowing that brains and bodies are both physical entities, but we appreciate that the ghost of dualism lingers.
In practice, to study the brain scientifically we have to make some choices. If, for the moment, we choose to limit ourselves to just looking at sensory-motor neural circuits, what matters is the anatomical pattern of connections between neurons and the physiology of the type and timing of the chemical and electrical signals operating within the circuit.[86] To understand how any circuit functions, you also need to be able to measure when the circuit is active relative to when the animal possessing that circuit is doing something. Once you establish this correlation between a circuit’s activity and the animal’s behavior, then you need to test whether or not that circuit is necessary and sufficient for that behavior. You can test for necessity by removing the circuit genetically or surgically and then seeing how behavior changes.
Sufficiency is much harder to show: the activity of the circuit, independent of other circuits, must be able to cause the behavior previously correlated with the circuit’s activity. To achieve the isolation that sufficiency demands, often the only way to go is to simulate the circuit on a computer or in an autonomous robot. The problem with simulation, as we’ve seen throughout this book, is that critics see simulation as “only” simulation, a model and not the thing itself.
Another way to show that a neural circuit is sufficient for a specific behavior is to find a “simple” animal—usually an underappreciated and overworked invertebrate sea slug, nematode worm, or fruit fly—that has the behavior and the circuit of interest but doesn’t have all the other neural machinery vertebrates possess to complicate the analytical situation. The great power of the basic brains of invertebrates is that we can identify each neuron and its connections, something that remains nearly impossible, in practice, in vertebrates. With just a few overlapping circuits operating to move, find food, and mate, invertebrates have become powerful tools for neuroscientists. Using invertebrates as model organisms, neuroscientists have identified multiple circuits that are necessary and sufficient for escaping, digesting, flying, and learning.
Neural circuits get linked to behavior in two related fields called “behavioral neuroscience” and “behavioral neurobiology.” Thomas Carew, professor of neurobiology and behavior at the University of California at Irvine, has made the strong argument that invertebrates help us understand the basic principles of anatomy and physiology that create the neural circuits that are necessary and sufficient to explain how animals behave.[87] And using general principles gleaned from invertebrates, along with the experimental approaches outlined above, neuroscientists are able to understand some behaviors in vertebrates. The most thoroughly understood behaviors, with mechanisms examined at the molecular through the behavioral levels, are echolocation in bats, hunting in owls, and navigation in rats.[88]
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Howard Gardner,
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This is why, by the way, we do spend time on neuroscience in
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A great place to start is with this book: Patricia Churchland,
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If you care about building intelligent machines, you must read this book: Jeff Hawkins and Sandra Blakeslee,
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Steven Vogel and Stephen A. Wainwright,
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Descartes is often considered to be the father of cognitive science because he approached the mind-body problem rationally and scientifically. Even though substance dualism was quickly, even in his day, refuted as a scientific theory, we talk about it in cognitive science because it underwrites so much of our intuition about minds, souls, ghosts, and heaven. For an introduction to dualism, visit the Stanford Encyclopedia of Philosophy: \plato.stanford.edu/entries/dualism/#SubDua, or read chapters 1 and 2 in Maslin,
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This paper does a great job explaining neural circuits and their functions: D. W. Tank, “What Details of Neural Circuits Matter?”
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Talk here of circuits and what’s necessary and sufficient to show causal relations of neural circuits to behavior are largely drawn from his book, which I strongly recommend: Thomas J. Carew,