The nature of the brain’s “representations”—if there is such a thing—of the world, the self, the past and present, remains puzzling, as the very different approaches we have described suggest: Changeux’s view of “long-lasting global representations”; Edelman and Tononi’s view of memory as constructive recategorizations, and Rizzolatti’s stunning discovery of mirror neurons, suggesting that we know and understand others, to some extent, through neural imitation. And as these differing views show… we are still far from a full understanding of the nature of memory, perception, and meaning.
So Israel Rosenfield, a doctor and historian, and Edward Ziff, a biochemistry professor, conclude their review How The Mind Works: Revelations in a forthcoming New York Review of Books piece. What I liked about this essay is its clear statement on starting points to think about our brains and its insightful summaries and critique of recent work. But in the end I was still left with a “So what?” Their hints at subjective psychology, the acting brain, and relational representation remained the side dishes, rather than the main course. I’ll deal with that main course later this week, and in this post cover Changeux and Edelman.
Rosenfield and Ziff give us a quick historical summary of work on the neuron as a cell that uses electrochemical signaling. Early research by Hermann von Hermholtz and Santiago Ramon y Cajal contributed to defeating the notion that neurons functioned in a similar fashion to the dominate communication technology of that time, the telegraph. Neurons are slow in direct contrast to the speedy telegraph.
Today we still draw on an equally speedy but wrong view, the computer analogy. Jean-Pierre Changeux helped overturn the computer view using both basic research and basic biological theory, evolution by natural selection. (Still, I was left asking myself, why couldn’t we have learned from the failure of the telegraph model in the first place…)
As Rosenfield and Ziff note, Changeux’s research showed that “the human brain therefore does not make optimal use of the resources of the physical world; it makes do instead with components inherited from simpler organisms… that have survived over the course of biological evolution.”
I read Changeux’s book Neuronal Man in graduate school, and it was formative in my own thinking about the brain. L’Homme Neuronal was published in 1983, and the English translation in 1986, when the computer model of the mind and the gene-centered view of our human nature were in ascendance. Indeed, those two got linked the following year in the foundational publications by Tooby & Cosmides in evolutionary psychology.
Changeux argued something completely different—the importance of the basic mechanisms and processes of the brain, the power of epigenetics and brain-environment interactions, and the role of natural selection in shaping the brain in the past and in present. As an Amazon reviewer puts it about a more recent Changeux book, The Physiology of Truth, this work “offers an evidence-based challenge to two popular ideas: namely, the largely functionalist idea that the brain is nothing more than a sophisticated computer and, alternatively, the nativist idea that the brain is ‘the embodiment of a strictly predetermined genetic inheritance’.”
For many years, Changeux has also been after bigger fish, moving from neurons themselves to neuronal communication and systemic brain function. Rosenfield and Ziff’s briefly summarize two main ideas, Hebbian learning (neurons that fire together, wire together) and specialized neurotransmitters released by regulatory networks that can reinforce neuronal connections throughout entire sections of the brain. Changeux’s long-term work has focused on those regulatory networks, in particular on the neurotransmitter acetylcholine:
It was long known that nicotine acts on the same receptor as the neurotransmitter acetylcholine. Changeux recognized that this could explain both nicotine’s obvious benefits—greater concentration, relaxation, etc.—as well as the drug’s more puzzling long-term effects… Changeux found that nicotine, by attaching to the same receptors as acetylcholine, reproduces some of the benefits of acetylcholine by reinforcing neuronal connections throughout the brain. Nicotine is not exactly the same chemically as acetylcholine, but can mimic its effects. Changeux’s lab has since focused on the workings of the nicotine/acetylcholine system, and he has attempted to explain how all such regulatory systems, working together, can produce the experience we call consciousness—as well as more abstract concepts like truth.
How does such a thing happen? Along with Gerald Edelman, Changeux has long been a proponent of neuronal selection. Too many neurons and connections are created during development to survive; selection of those neurons and connections that work best together results in a better functioning brain.
In Changeux’s view, starting in the womb, spontaneous electrical activity within neurons creates highly variable networks of nerve cells; the networks are selected and reinforced by environmental stimuli; and these reinforced networks can then be said to “represent” the stimuli—e.g., the appearance of a predator—though no particular network of nerve cells exclusively represents any one set of stimuli. The environment does not directly “instruct” the brain; it does not imprint precise images in memory. Rather, working through our senses, the environment selects certain networks and reinforces the connections between them.
Through this process of “learning by selection,” Darwinian competition works to strengthen “some of these transient networks sufficiently to make them relatively permanent parts of the child’s behavioral repertoire.” By combining learning by selection and his work on the physical functioning of the brain, Changeux has also argued for an objective representation of “truth” by the brain. He writes, “[though] the precise patterns of connectivity in the network may vary from individual to individual… its functional relationships (or stabilized meanings) remain constant. In this way a ‘scale model’ of external reality… is selected and stored in memory in the brain. Memory objects enjoy a genuine existence, then, as latent ‘forms’ composed of stable neuronal traces.”
Rosenfield and Ziff see this last move by Changeux as going too far, reducing memory and meaning to only a “matter of reconstruction of latent physical traces.” But there is another way to read other parts of Changeux. For example, in The Physiology of the Truth Changeux writes, “It is generally accepted today that distinct populations of neurons in sensory, motor, associative, and other territories are linked as part of a distributed network… [which] mobilizes several distinct and functionally specific territories in a discrete manner, thus constituting a neural embodiment of meaning.”
In my mind, this is a good statement on the “state of the science,” similar to when Changeux started his own work on neurotransmitters and synapses. Today we don’t just have neurons as electrochemical and Hebbian and neurotransmitter-driven changes in neuronal function. We have distinct populations working together in distributed networks, and which help constitute the neural embodiment of meaning.
The adjective neural is important there, for it’s when Changeux takes the next step to say that this neural embodiment physically constitutes meaning that the problems start. Neuronal selection and embodiment and populations of distinctly functioning neurons are important, but together these two do not constitute meaning.
The brain is housed in a body. Individuals are linked by relationships and language. Individuals come together in social groups such as families. Around all of that are the social and cultural traditions that shape relationships, language, and social groups, and thus directly impact the neural embodiment of meaning.
This sort of view of the brain is behind Rosenfield and Ziff’s turn to Gerald Edelman: “In contrast to Changeux’s account, Edelman, we believe, has a different and considerably deeper view of memory and what it tells us about the nature of meaning and brain function.” They review Edelman’s 2001 book, written with Giulio Tononi, A Universe of Consciousness: How Matter Becomes Imagination.
(You might also see Edelman’s more recent Second Nature: Brain Science and Human Knowledge, which addresses the Two Cultures divide, the future of brain technologies, and the neuronal basis of knowledge; that said, I saw Edelman speak once, and saw a man in desperate need of some anthropology and a bit more humility about his conviction that he alone can explain everything.)
Why do Rosenfield and Ziff like Edelman’s account better? His account of memory focuses on the ability to “repeat a mental or physical act after some time despite a changing context… In mentioning a changing context, we pay heed to a key property of memory in the brain: that it is, in some sense, a form of constructive recategorization during ongoing experience, rather than a precise replication of a previous sequence of events.”
Action, context, experience, all these are closer to the quick of life rather than a precise replication. Indeed, constructive recategorization is an excellent Darwinian metaphor for how variation and function come together. Changeux’s model falls back on a neuron-centered view, despite his critique of a gene-centered view.
Edelman writes that “the key conclusion is that whatever its form, memory itself is a [property of a system]. It cannot be equated exclusively with circuitry, with synaptic changes, with biochemistry, with value constraints, or with behavioral dynamics. Instead, it is the dynamic result of the interactions of all these factors acting together, serving to select an output that repeats a performance or an act.”
Still, Edelman and Tononi are just notching things up one level to a brain-centered view. “Perception is not merely a reflection of immediate input,” they write, “but involves a construction or a comparison by the brain.” The system is the brain, while our senses are “confronted by a chaotic, constantly changing world that has no labels.”
Niche construction theory in evolution, ecological psychology’s affordances, and the systemic properties of culture could all have helped here, worked into the sort of dynamics that Susan Oyama and Ester Thelen consider.
That said, Jean-Pierre Changeux and Gerald Edelman have helped neuroscience forward through both basic research and through thinking outside the box. And this sort of research helps position neuroscience for becoming part of the conversation on how niches are constructed and how culture works.