LIN5000 Forum topic 2.1: Lateralisation and modularity

Some of the most important evidence for the lateralisation and modularity of language has come from investigating brain-damaged individuals. Do you think this is a good strategy? Why (not)?

In the journal Neuroscience, Chris Rorden and Hans-Otto Karnath (2004) explore neurolinguistic research focused on patients with brain lesions ('brain-damage' as per the topic question) in the 1860s, and again in the 1950s and '60s, and acknowledge this research provided insights into lateralisation and modularisation that are an "enormous contribution ... to our understanding of the human brain". However they go on to identify limitations of this research:

1. The research is based on lateralisation and modularity as established assumptions that do not allow for the existence of any degree of distributed processing, that is, parts of the brain working together in a plastic fashion
2. The brain-damage within regions of the brain in question is rarely limited to just that region - this damage is  typically caused by oxygen starvation (e.g. as the result of stroke, etc.) to a more general area of the brain, and the assumptions drawn from these studies cannot be isolated only to the specific physical areas of study
3. The very plasticity of the brain allows it to 'rewire' to compensate for such damage - as discussed in the text - in various degrees and with varying success depending on factors including age, and the research does not address 're-routing' changes in process as a result of plasticity, after injury. That is, the research does not "allow access to the time-course of information processing"

I also believe that while the early research was critical to current and future understanding it is limited in two ways: first, the research sample was restricted to patients with existing brain damage only; and second, the research (by nature) could not compare the capabilities of patients individually, pre- and post-injury.

So, from a perspective of scientific method, the research had great limitations. In terms of value to the field, it was foundational and ground-breaking.


References
Rorden, C., and Karnath, H. (2004). Using human brain lesions to infer function: a relic from a past era in the fMRI age? Nature Reviews Neuroscience. doi:10.1038/nrn1521
Available from http://faculty.washington.edu/somurray/psych506/readings/lesion-methods.pdf