The Physiology of Truth: Neuroscience and Human Knowledge

Biology 202
2006 Book Commentaries
On Serendip

The Physiology of Truth: Neuroscience and Human Knowledge

Gray Vargas

In this wide-ranging book, Changeux takes up the challenge, much as this class did, of explaining how truth and reality are present in the brain and its activity. He is interested in how consciousness arises and checks reality, and how the world is perceived so similarly by different individuals. While Grobstein believes that there is no truth in science, there is only "getting it progressively less wrong," Changeux devotes an entire book to the search for truth and how it exists in neural processing. While Grobstein thinks that there are only "stories in our heads," most of us want to believe that there is some sort of absolute truth (that the book I see is actually there), and Changeux tries to wrestle with where this absolute truth lies in terms of the workings of the brain.

He begins the book by giving a brief background on the micro end of the nervous system—examining the workings of neurons, proteins, receptors, ion channels, neuronal plasticity, hierarchy, and integration of neuronal information. In general, Changeux is in awe of the brain and describes it as an open, motivated, and self-organizing structure. Like Grobstein, Changeux believes in materialism, such that even the most complex thoughts and behaviors can be ultimately explained by workings of neurons—believing the brain is, in Voltaire's terms, "thinking matter." Both individuals also believe in the brain's ability to show spontaneous, organized activity without input (centrally generated patterns).

While over-simplified, Changeux's explanation of the evolution of the brain and nervous system interested me. He explained that as organisms evolved to be multicellular, a nervous system came about in order to regulate internal functions, representations of the external world, and the agreement of these representations with the facts of the world (the piece he is most interested in). Basically, it is the nervous system's job to make our internal representations of the world match what is "out there." (This checking or matching is what is abnormal in delusional/psychotic states.) And each organism, interestingly, devises representations of the world which favor its survival. According to Changeux, truth is when thoughts equal reality and consciousness is a way of evaluating truth that is useful to the survival of the species. This evolutionary perspective is one that was not presented in class, and which is a very interesting addition to the conversation on consciousness.

As the nervous system evolved to be more complex, it became hierarchical, began showing parallel processing, and organisms began to more thoroughly investigate their world and picture the world and themselves in it (the I-function piece Grobstein discusses). This is evolutionarily the most recent piece, and the piece which might set us apart as humans. Changeux argues that as brains gained more plasticity more learning occurred, but he gives no evidence for why this might have been, and it is not clear why the causality would only be in this direction. But he does believe that every organism has an "instinct to learn" that is necessary for its survival (to eat, drink and mate you usually need to explore the world).

The big question, with all of this more complex, hierarchical and parallel processing, is how truth is established or verified. (Why, because I can see that apple, does it mean that it is really there?) The main question here is what the representation of the world looks like in individuals, and how it can be so similar in different people. This is especially intriguing because, as Changeux mentions, some people believe that no object "has ever been or can ever be represented in the brain in any form." (This goes against what we learned in class that objects, or reality, only exist in the brain.) That is, reality can never exist as it is in the brain, and it cannot be represented identically in everyone since neuronal structure and connections differ between individuals. Yet individuals behave remarkably similarly, and we can understand each other, so there must be some basic set of representations or concepts common to all human brains. These are what Changeux is fascinated by. He wants to know how common "mappings" between connections and behaviors are established. He never really answers this question, but hints that part of the answer might lie in temporal synchronization of neuronal firing—which he says integrates and coordinates actions of connected groups of neurons.

One angle Changeux takes to try and describe how we devise our representations, is through development. He claims that as we develop we use "cognitive games," also known as thought experiments, in which we test hypotheses/pre-representations about the world in a trial and error fashion (getting it less wrong!). In this way we are able to recognize and categorize the world. The more experienced we become the fewer experiments we need to make, as we "learn to eliminate." Again, Changeux does very little explaining of what actually changes during this learning process, besides perhaps more synchronous neuronal firing, more firing in general, and/or a more precise distribution of firing. This neural basis of learning and discussion on development was really not tackled in the class, and might be a useful way of describing how nervous systems are similar/different across individuals.

One large question that is very central to the class as well as the book, is how consciousness arises from neurobiological processes. How is consciousness, or our sense of "I" (I-function), a "pattern of action potentials," when it seems for all the world that the sum is greater than all of the parts? Again, both Changeux and Grobstein know that it must lie in the workings of neurons, and in the more recently evolved brain regions at that. Changeux claims that it is some sort of combination of sensation and memory, but he is perplexed as to how it is so consistent over time. Like Grobstein's model, where the I-function is a box with arrows pointing in and out of it, Changeux explains consciousness as an "open-loop phenomenon with entries and outlets in constant mutation." But he does not explain this loop or these entries/outlets in any further detail. While Grobstein pinpoints the I-function to the neocortex, Changeux does not name any specific regions of the brain. Changeux is more interested in how these regions (whatever they are) decide what is true and false out of the knowledge they acquire. Changeux actually seems to suggest that at a certain point consciousness cannot be studied (he compares it to studying someone's reaction to a painting) and that introspection is the only way to study certain complex thought processes. In general, throughout the book, Changeux mainly points out the tasks of neuroscience as a whole, instead of really answering a lot of his own questions (somewhat like the class in this way).

Like in class, Changeux looks to sleep/hallucinations/anesthesia to try and explain the neural basis of consciousness. He actually links the two, showing that in REM sleep, and during hallucinations in one schizophrenic patient, there are activations in auditory and visual areas but not in the prefrontal cortex (PFC). He is thus implying that the PFC might be involved in important conscious reality testing, as Grobstein also suggested. He also mentions that from chimpanzees to man, there is a 70% increase in the number of possible neural connections in the PFC, further suggesting that some of what makes us human might lie in this region.

Another interesting topic not covered in class, but related to the idea of evolution, is the effect of genes on the brain. Changeux devotes an entire chapter of his book to this question, and seems to believe that the brain is constrained by our limited number of genes, an idea I had never come across or thought of. (He claims that there are about 30,000 genes responsible for about 100 billion neurons in the brain, and so there is limited genetic information for constructing the brain.) He does not go on to explain what this limitation would mean in terms of brain development, but it would seem to suggest that this might be a reason we all have a good amount of similar brain networking, since such a small percentage of our genes varies from person to person.

In the end of his book, Changeux discusses the scientific method, technology, and the need for a sharing of scientific knowledge across cultures. His main point is that scientific research is motivated by the search for knowledge that has universal truth, but yet the knowledge obtained is not used universally for everyone who needs it (third world countries, etc). Therefore, he thinks that there should be more scientific discourse and debate and no beliefs or ideologies specific to certain local regions of the world. Thus, science has a moral obligation to "inspire and direct the campaign for human rights." His other main thesis is that obtaining objective knowledge about brain functioning will allow us to get a deeper understanding about what makes us human, and thus will increase tolerance and mutual respect, as we see ourselves as one "social species which is a product of biological evolution." In class, we mentioned how we are influenced by and influence our culture, and how everyone's brains and nervous systems are therefore connected, but we did not discuss human rights worldwide as they relate to scientific advances. Grobstein and Changeux both believe that cultural/individual differences give us the chance to "more efficiently test the truth of acquired knowledge" and thus that individual variability is key in how we understand the world—and Changeux focuses on the importance of language as a mechanism for how knowledge is shared.

Like the class, Changeux seems to have a philosophical slant, which seems to be the direction we go when we have run out of ways to explain these functions in terms of the micro-level information we have available, and try to fill in the holes in our present knowledge base. While the class focused on a very specific range of topics and went into great depth about the actual neural processes involved (with the intention of being able to generalize these processes across various input or output systems), the book tried to focus on too many topics and did not go into any in sufficient depth, or with sufficient scientific evidence.