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“The Knowledge” of a London Taxi Driver

2/13/2016

5 Comments

 

by Edward Quinn

​Our readings this week focus on the embodied effects of training in specific subcultural contexts. A very interesting example of this phenomenon can be found among taxi drivers in London. Becoming a taxi driver in London is an arduous, 3-4 year process that is cognitively demanding. Taxi drivers must learn the spatial characteristics of an area within 6 miles of Charing Cross train station, which contains roughly 25,000 streets. Only about half of the people who set out to become a taxi driver in London typically complete the training and exams required for qualification.
 
The hippocampus is an area of the brain that is associated with memory formation and spatial navigation, so it is reasonable to infer that the hippocampus is a particularly important brain structure for a London taxi driver. Woollett and Maguire (2011) build on previous cross-sectional studies showing greater gray matter volume in the posterior hippocampi of taxi drivers compared to matched controls who were not taxi drivers. Using a longitudinal research design with two time points, the authors tested the hypothesis that what drives these observed differences in the hippocampus is the 3-4 year taxi driver training process of acquiring “The Knowledge” of London’s spatial characteristics. They started off with two groups at Time 1 (taxi driver trainees and matched controls) and ended with three groups at Time 2 (qualified taxi drivers, failed taxi trainees, and controls).
 
The authors found confirmatory evidence for their hypothesis. Qualified taxi drivers showed increased gray matter volume in the posterior hippocampus compared to matched controls and the group of failed taxi trainees at Time 2. The longitudinal research design lends particular strength to these findings, and gives us a reasonable basis for inferring cause and effect. In addition, the authors show that qualified taxi drivers actually performed worse than the control group on a memory recall test of a complex figure at Time 2, but not at Time 1.
 
This last point is interesting because it suggests that there may be a cost to cognitive specialization driven by culturally specific training regimens. The training regimes people subject themselves to enable adaptation to particular demands, and this is a good thing so long as the demands do not change. It may be the case that the structural changes associated with qualification as a taxi driver actually inhibited performance on a short term (30 minute) memory test. If this is the case, it would be interesting to further explore not only the strengths people are able to develop through intense training, but also what weaknesses come as a cost of that same training.
 
From a neuroanthropological perspective, we might have predicted that the training regime of London taxi drivers might be embodied in the form of structural changes in the brain. While MRIs provide a method of testing this idea, it might be enhanced by doing the ethnography of a London taxi driver. It would be interesting to hear how a London taxi driver describes the training process, and ethnography may corroborate the findings of Woollett and Maguire (2011). Also, neuroanthropologists place great emphasis on the importance of environmental input for the developing brain, with less emphasis on adult plasticity. This study used groups of men with average ages of 35, 38, and 41, thus providing an example of plasticity in the brain long after development is complete. It is important to remember that enculturation of the nervous system does not end with development, as clearly demonstrated by the taxi drivers of London.  
 
Overall, this is a great article with interesting implications for neuroanthropology. The idea that training regimes come with not only adaptive benefits, but also costs is an idea that deserves to be further explored. In neuroanthropology, plasticity in adulthood seems to receive less attention than plasticity in developmental stages of the life course, but this study shows that plasticity can be important in adulthood as well. The longitudinal research design lends great strength to the evidence for the embodied effects of training to be a taxi driver in London, and neuroanthropologists might benefit greatly from implementation of strong research designs such as the one used by Woollett and Maguire (2011).
 
Reference:
 
Woollett, Katherine, and Eleanor A. Maguire. 2011. "Acquiring ‘the Knowledge’ of London's layout drives structural brain changes." Current Biology 21(24): 2109-2114.
5 Comments
Michelle Bird
2/17/2016 09:11:25 am

This article seemed incredibly interesting to me, and a much of what is discussed makes tremendous sense. Personally, I've encountered many similar situations myself, but never really realized the full effect of my actions. Everything from practicing proper marching technique in the band to learning how to navigate a new city affects the brain, and while I'd had the experience of acquiring new (or improving) skills, I'd never paid much attention to what was lost in the process. The implication that more grey matter equates to poorer recall caught my eye. I remember reading last week that women have, on average, more grey matter than men do, which further expands during pregnancy (I thought it was likely because women are biologically predisposed to become caretakers of infants, and thus would need the added amount of perceptibility in order to complete that task and care for themselves effectively), and the experience I've had with pregnant women has indicated that memory troubles do indeed become prevalent, especially in the final weeks of the pregnancy. That this same phenomenon can occur in men who are well out of any brain developmental stages is fascinating, and could drastically change the way we perceive higher intelligence in general. It would make sense that by refining a person's sensory perception (ability to adapt, really), their need for memorization skills would decrease, especially in a familiar environment.

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Jake Aronoff
2/17/2016 09:20:56 am

This was very interesting to read, and the two points that stuck out to me were the idea of costs associated with specialized brain functioning and adult brain plasticity. On Molly's blog post, Mirjam commented, "This quote perfectly sums up the point of the chapter (Balancing between Cultures, by Greg Downey), and perhaps the whole field of neuroanthropology:
“ The nervous system is always training, becoming better adapt to our patterns of living, recalibrating to the situations we place ourselves in and transforming our biographies into our biology” (p. 188)".

Based on this quote, it is very interesting that you highlighted the age of the participants in the study, and I think rightly highlighted that adult brain plasticity is largely ignored in scientific research. While it seems a safe assumption that plasticity is greatest early in life (especially when considering the idea of neuronal group selection- Downey & Lende 2012 P.116), the quote Mirjam highlights also shows (as well as the two chapters assigned for this week in general) that the nervous system is always capable of some level of plasticity and recalibration.

Another interesting point you highlighted was the cost that comes with specialization. This reminded me of an article I just read by Worthman (2009) titled, "Habits of the Heart: Life History and the Developmental Neuroendocrinology of Emotion" that addressed costs associated with regulating cognitive resources, such as attention and memory. With limited resources at our disposal as organisms, we must decide (a decision shaped through experience, such as taxi driver training) what is crucial and what is less important to our survival and direct our resource allocations accordingly.

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Jake Aronoff (2nd Post)
3/1/2016 05:18:26 pm

I've placed my second comment with my first, though my second comment will actually address the Downey reading.

Downey terms equilibrium as a "sensory system" and writes, "Horak and Macpherson (1996) argue that redundancy in the system is absolutely necessary to resolve the ambiguities that occur when different sensory channels offer conflicting information about posture and balance" (173). This compromise between efficiency and redundancy is a theme I keep seeing. In the equilibrium sensory system, redundancy is required, but only to a certain extent, as having several sensory inputs is costly and burdensome for an organism.

I also saw this theme when reading about degeneracy in biological systems theory. Degeneracy in biological systems theory refers to the ability of different structures to perform the same function. The compliment to this is pluripotentiality, where one structure can perform multiple functions (Noppeney et al. 2004). These processes occur at a compromise between efficiency and redundancy. For example, having multiple brain structures capable to performing the function is good in case one structure fails. However, having multiple structures to perform the same function is redundant and therefore inefficient. Degeneracy and pluripotentiality allow this compromise between redundancy and efficiency, as it allows multiple and different structures to exist that perform different functions under some conditions and the same function under other conditions (under condition A, structure 1 and structure 2 perform different functions, but under condition B, structure 1 and structure 2 perform the same function) (Noppeney et al. 2004). This allows efficiency where under some conditions there is a "one-to-one" structure-function relationship, but also provides necessary redundancy or "cover" for when multiple structures are needed to perform the same function.

The third case where I saw this compromise between redundancy and efficiency was during the cultural evolution of language ALLELE talk by Dr. Christiansen. During the QandA, someone in the audience noted that there is not an all-encompassing trend toward reducing the complexity of languages. Dr. Christiansen responding by saying this is because there must be a compromise at some point between efficiency and redundancy in language. He said that the most efficient language use would be to just say something like "blah, blah, blah" (his words) and still understand each other. However, he noted that some redundancy is necessary, because the reduction in complexity of language use reaches a certain point where redundancy is necessary for the listener to still be able to understand what is being said even if they don't hear or understand one part of what the speaker is saying.

Noppeney, U., Friston, K. J., & Price, C. J. (2004). Degenerate neuronal systems sustaining cognitive functions. Journal of Anatomy, 205(6), 433-442.

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    This blog is group authored by Dr. DeCaro and the students in his ANT 474/574: Neuroanthropology.

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