Neural Substrates of Symbol Use
Chris Chatham, a graduate student at Boulder and a leading neuroscience blogger on ScienceBlogs.com, has a couple of recent posts about symbol uses (The Blessing and Curse of Analytic Depth in Understanding Symbol Use, Neural Substrates of Symbol Use).
He offers the following in the first post:
Conclusions
The cognitive neuroscience of high-level cognition is stretched thin with tension between the too-complex and the too-simple, as demonstrated above in the sample domain of symbol use. In seeking to explain complex behavior, neuroscience has isolated myriad neurobiological mechanisms which seem too simple and narrow to explain something like the use of symbols. (And I imagine these tensions are not unique to brain science).
Reconstructionist approaches may provide a solution to the dilemma between the study of intractable complexity on the one hand and the methods of narrow reductionism on the other. Computational modeling can specify how these reduced components give rise to large-scale behavior, and how to actionably and mechanistically understand such behavior in clinical or applied settings.
And this is the blessing of analytic depth - reconstructionist and integrative approaches can pull from multiple levels of analysis to provide a more coherent and actionable understanding of natural phenomena than the "infinite reduction" method dominating mainstream science.
In the 2nd post he focused on a chapter by Randall O’Reilly on connectionist modeling of balance among brain regions, which is quite interesting (read: enjoyed reading but not knowing how to respond). Chris’s post, though, seems to have a logical fallacy that may reflect a tendency of a young science to look away from history. He listed a number of characteristics of symbols — in my mind these are specific to symbol systems, not individual symbols — and argued about what kind of brain mechanism can support these requirements. This is half-way backward. A euqally valid question is how is the development of symbols and symbols systems constrained by brain mechanisms. This would require looking at the evolution (not in the Darwinian sense) of symbols.
Maybe it’s just me, but I was more than a little turned off by Chris’ logic in assigning brain regions to symbolic functions in post 2. I don’t have time to articulate it further today, so I will leave it right there. Suffice it to say that it reflects exactly what Chris concluded in the first post, that neuroscience is stretched thin between reductionlism and everyday complexity.
May 7th, 2008 at 9:06 am e
Just discovered your excellent blog by looking for diffusion models.
I know that I didn’t solve the “symbol problem” (to the extent there is one) in that post, but I don’t understand the thrust of your criticism. The following views about the functionality of various brain regions are broadly shared in cognitive neuroscience:
- rapid binding of arbitrary information via hippocampus
- temporal cascades of representation in prefrontal cortex, with increasingly abstract representations in more anterior regions
- compositional features of objects and information in temporal cortex
I think it’s fairly straightforward to see how each of those functionalities might contribute to symbol processing/systems, and I don’t understand why this would be distasteful to you.
Whether symbol systems are somehow “constrained” by brain functionality is to me a non-issue and not tractable by empirical research. The claims I make in the post are.
May 7th, 2008 at 12:08 pm e
sorry, to clarify: by “not tractable” I mean it’s impossible to empirically verify if symbol systems would be different if we had different brains, based on the large cultural dimension to symbol systems.
Of course it’s possible to look at language and mathematics (etc) in brain damaged patients, or after TMS. Those would certainly be informative, but primarily for understanding how the brain supports symbol processing, and not how symbol processing is constrained by the brain (assuming that brain damage and TMS reduce symbol processing capacity).
May 8th, 2008 at 1:59 am e
Chis,
Thanks for the comments. I struggle with the same questions and am not sure if (and when) I will have clear, well thought out answers. But here are a couple of illustrations of how I see the interdependencies of the brain and symbol systems.
1. Take music. We can ask (a) what kind of brain mechanisms support the kind of songs homo sapiens sing, or (b) what kind of songs can we sing given the brain we have. Neither sounds like the right kind of question. And we probably have to take an interactionist perspective here. I guess that’s what I meant by “half-way backward” (a year ago).
2. Take the Word Form Area, which is arguably a unique brain structure with certain specificities to symbol strings, particularly written symbols. What was the function of the WFA 6000+ years ago before we had writing? Actually, until 13th century most people rarely got to see printed words. On the other hand, while not all writing systems are linear or of the size that WFA likes, the most successful ones — the ones survived — are. Was WFA “evolved” to support writing? Unlikely. Was writing evolved by exploiting a region that sat there idling (or not) 6000 years ago? How did the creators know WFA was the target to take advantage of? Chances are different early writing systems (or rather, attempts to write) were all supported by the brain (tautology? No, if you consider individual differences), but more specific brain functions for reading “co-evolve” with the symbol system in a non-Darwinian sense (I guess I mean optimization rather than selection).
Again, I realize I am not making a completely coherent argument here. But I hope I have shown why I didn’t like the 1-sided question on brain and symbol systems, and why I have always had a gut feeling whenever I see functions being labeled on brain parts. In my mind it only makes sense to say Brain Region X does Function Y given a task structure Z, which itself is defined — evolutionarily, culturally, or otherwise — as a function of all regions {X at t-1} that do {Y at t-1} given task {Z at time t-1}. You know what I mean. The region, function, and task has to be understood in this history of optimization.
Tractability — I happen to believe it’s much more tractable than evolutionary problems, but with the same logic, i.e., by looking at historical changes in symbol systems, and by comparing the evolution (non-Darwinian sense) and current state of different symbol systems.
Regards,
– gary
May 8th, 2008 at 10:38 am e
I think these are two separate issues:
1) “I didn’t like the 1-sided question on brain and symbol systems, and
2) “why I have always had a gut feeling whenever I see functions being labeled on brain parts.”
Re 1, I can understand why one might prefer one question over the other - it’s a question of focus (are you interested in the cultural ramifications of neuroscience, or are you interested in understanding how the brain generates behavior).
Re 2, I think this is a common response to cognitive neuroscience. It was my response before I began studying it.
But obviously we need to employ some reductionism; otherwise we can’t use scientific methods study the brain as the completely distributed, bidirectionally-interacting (with itself and with culture/context) it is. But we can begin to reconstruct the results of reductionism through techniques like computational modeling. Those efforts are not at the point where cultural effects emerge, but they do provide hints as to what the contributions of various brain regions might be to that larger interacting system. That is the approach I take, and which responsible cognitive neuroscientists take, in ascribing functions to various brain regions. In the context of symbol use I still think my descriptions are in keeping with those principles as best we can now.
On the other hand, that post has not been particularly popular, and the essay exam of which it was a part didn’t get a perfect grade, so you are not alone in disliking that (or some) aspect of it