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Neuropath / Re: Countering the Argument with Thorsten
« Last post by H on December 09, 2019, 01:48:02 pm »Alex Rosenberg and Bakker are correct (AFAICTell) that the only conclusion for those committed to Physicalism is this seeming Aboutness has to be false in some sense, but I just cannot see how that could be.
From Rosenberg's latest book:
Quote
What makes the neurons in the hippocampus and the medial entorhinal cortex of the rat into grid cells and place cells—cells for location and direction? Why do they have that function, given that structurally they are pretty much like many other neurons throughout both the rat and the human brain?
From as early in evolution as the emergence of single-cell creatures, there was selection for any mechanism that just happened to produce environmentally appropriate behavior, such as being in the right place at the right time. In single-cell creatures, there are “organelles” that “detect” gradients in various chemicals or environmental factors (sugars, salts, heat, cold, even magnetic fields). “Detection” here simply means that, as these gradients strengthen or weaken, the organelles change shape in ways that cause their respective cells to move toward or away from the chemicals or factors as the result of some quite simple chemical reactions. Cells with organelles that happened to drive them toward sugars or away from salts survived and reproduced, carrying along these adaptive organelles. The cells whose organelles didn’t respond this way didn’t survive. Random variations in the organelles of other cells that just happened to convey benefits or advantages or to meet those cells’ survival or reproductive needs were selected for.
The primitive organelles’ detection of sugars or salts consisted in nothing more than certain protein molecules inside them changing shape or direction of motion in a chemical response to the presence of salt or sugar molecules. If enough of these protein molecules did this, the shape of the whole cell, its direction, or both would change, too. If cells contained organelles with iron atoms in them, the motion of the organelles and the cells themselves would change as soon as the cells entered a magnetic field. If this behavior enhanced the survival of the cells, the organelles responsible for the behavior would be called “magnetic field detectors.” There’d be nothing particularly “detecting” about these organelles, however, or the cells they were part of. The organelles and cells would just change shape or direction in the presence of a magnetic field in accordance with the laws of physics and chemistry.
The iterative process of evolution that Darwin discovered led from those cells all the way to the ones we now identify as place and grid cells in the rat’s brain. The ancestors to these cells—the earliest place and grid cells in mammals—just happened to be wired to the rest of the rat’s ancestors’ neurology, in ways that just happened to produce increasingly adaptive responses to the rat’s ancestors’ location and direction. In other mammals, these same types of cells happened to be wired to the rest of the neurology in a different way, one that moved the evolution of the animal in a less-adaptive direction. Mammals wired up in less-adaptive ways lost out in the struggle for survival. Iteration (repetition) of this process produced descendants with neurons that cause behavior that is beautifully appropriate to the rat’s immediate environment. So beautifully appropriate, that causing the behavior is their function.
The function of a bit of anatomy is fixed by the particular adaptation that natural selection shaped it to deliver. The process is one in which purpose, goal, end, or aim has no role. The process is a purely “mechanical” one in which there are endlessly repeated rounds of random or blind variation followed by a passive process of environmental filtration (usually by means of competition to leave more offspring). The variation is blind to need, benefit, or advantage; it’s the result of a perpetual throwing of the dice in mixing genes during sex and mutation in the genetic code that shapes the bits of anatomy. The purely causal process that produces functions reveals how Darwin’s theory of natural selection banishes purpose even as it produces the appearance of purpose; the environmental appropriateness of traits with functions tempts us to confer purpose on them.
What makes a particular neuron a grid cell or a place cell? There’s nothing especially “place-like” or “grid-like” about these cells. They’re no different from cells elsewhere in the brain. The same goes for the neural circuits in which they are combined. What makes them grid cells and place cells are the inputs and outputs that natural selection linked them to. It is one that over millions of years wired up generations of neurons in their location in ways that resulted in ever more appropriate responses for given sensory inputs from the rat’s location and direction.
Evolutionary biology identifies the function of the grid and place cells in the species Rattus rattus by tracing the ways in which environments shaped cells in the hippocampus and entorhinal cortex of mammalian nervous systems to respond appropriately (for the organism) to location and direction. Their having that function consists in their being shaped by a particular Darwinian evolutionary process.
But what were the “developmental” details of how these cells were wired up to do this job in each individual rat’s brain? After all, rats aren’t born with all their grid and place cells in place (Manns and Eichenbaum, 2006). So how do they get “tuned” up to carry continually updated environmentally appropriate information about exactly where the rat is and which way the rat needs to go for food or to avoid cats? Well, this is also a matter of variation and selection by operant conditioning in the rat brain, one in which there is no room for according these cells “purpose” (except as a figure of speech, like the words “design problem” and “selection” that are used as matters of convenience in biology even though there is no design and no active process of selection in operation at all).
Like everything else in the newborn rat’s anatomy, neurons are produced in a sequence and quantity determined by the somatic genes in the rat fetus. Once they multiply, the neurons in the hippocampus and the entorhinal cortex, and many other neurons in the rat’s brain as well, make and unmake synaptic connections with each other. Synaptic connections that lead to behavior rewarded by the environment, such as finding the mother’s teat, are repeated and thus strengthened physically (by the process Eric Kandel discovered; Kandel, 2000). Among the connections made, many are then unmade because they lead to behaviors that are not rewarded by feedback processes that strengthen the synaptic connections physically. Some are even “punished” by processes that interrupt them. In the infant rat, the place cells make contact with the grid cells by just such a process in the first three weeks of life, enabling the rat’s brain to respond so appropriately to its environment that these cells are now called “place” and “grid” cells (O’Keefe and Dostrovsky, 1979). Just as in the evolution of grid and place cells over millions of years, so also in their development in the brain of a rat pup, there is no room whatever for purpose. It’s all blind variation, random chance, and the passive filtering of natural selection.
These details about how the place cells and the grid cells got their functions are important here for two reasons. First, they reflect the way that ’natural selection drives any role for a theory of mind completely out of the domain of biology, completing what Newton started for the domain of physics and chemistry. They show how the appearance of design by some all-powerful intelligence is produced mindlessly by purely mechanical processes (Dennett, 1995). And they make manifest that the next stage in the research program that began with Newton is the banishment of the theory of mind from its last bastion—the domain of human psychology.
Second, these details help answer a natural question to which there is a tempting but deeply mistaken answer. If the grid cells and the place cells function to locate the rat’s position and direction of travel, why don’t they contain or represent its location and direction? If they did, wouldn’t that provide the very basis for reconciling the theory of mind with neuroscience after all? This line of reasoning is so natural that it serves in part to explain the temptation to accord content to the brain in just the way that makes the theory of mind hard to shake. By now, however, it’s easy to see why this reasoning is mistaken. For one thing, if the function of the place and grid cells really makes them representations of direction and location, then every organ, tissue, and structure of an organism with a function would have the same claim on representing facts about the world.
Consider the long neck of the giraffe, whose function is to reach the tasty leaves high up in the trees that shorter herbivores can’t reach, or the white coat of the polar bear whose function is to camouflage the bear from its keen-eyed seal prey in the arctic whiteness. Each has a function because both are the result of the same process of random or blind variation and natural selection that evolved the grid cells in the rat. Does the giraffe’s neck being long represent the fact that the leaves it lets the giraffe reach are particularly tasty? Is the coat of the polar bear about the whiteness of its arctic environment or about the keen eyesight of the seals on which the bear preys? Is there something about the way the giraffe’s neck is arranged that says, “There are tasty leaves high up in the trees that shorter herbivores can’t reach”? Is there something about the white coat of the polar bear that expresses the fact that it well camouflages the bear from its natural prey, seals? Of course not.
But even though they don’t represent anything, the long neck of the giraffe and the white coat of the polar bear are signs: the long neck is a sign that there are tasty leaves high in the trees on the savanna, and the white coat is a sign that the bear needs to camouflage itself from its prey in the whiteness of the arctic, the way clouds are signs that it may rain. But for the neck and coat to also be symbols, to represent, to have the sort of content the theory of mind requires, there’d have to be someone or something to interpret them as meaning tasty leaves or a snowy environment. Think back to why red octagon street signs are symbols of the need to stop—symbols we interpret as such—and not merely signs of that need.
The sign versus symbol distinction is tricky enough to have eluded most neuroscientists. The firing of a grid cell is a good sign of where the rat is. It allows the neuroscientist to make a map of the rat’s space, plot where it is and where it’s heading. John O’Keefe called this a “cognitive map,” following Edward Tolman (1948). The “map,” however, is the neuroscientist’s representation. The rat isn’t carrying a map around with it, to consult about where it is and where it’s heading. Almost all neuroscientists use the word “representation,” which in more general usage means “interpreted symbol,” in this careless way—to describe what is actually only a reliable sign. (See Moser et al., 2014 for a nice example.) The mistake is usually harmless since neuroscientists aren’t misled into searching for some other part of the brain that interprets the neural circuit firing and turns it into a representation. In fact, most neuroscientists have implicitly redefined “representation” to refer to any neural state that is systematically affected by changes in sensory input and results in environmentally appropriate output, in effect, cutting the term “representation” free from the theory of mind, roughly the way evolutionary biologists have redefined “design problem” to cut it free from the same theory.
I too think Rosenberg and Bakker are "right" even if they aren't 100% correct necessarily. But, far be it from me to think I fully understand Rosenberg's point. I think you'd find the book interesting though Sci.