In a message dated 04/11/2009 22:57:17 GMT Standard Time, bhayenga at rrps.net 
 writes:

People with  acquired head injuries in the same brain areas implicated in 
the neuro-anatomy  and brain scan studies, suddenly have problems similar to 
many dyslexics.  Animals with induced brain injuries in those same areas 
have similar sensory  processing deficits. Genetic mutation studies implicate 
the same areas. Brain  scans show abnormalities in the function of those 
areas. Cognitive processes  known to be important in reading are tied to those 
same areas. A simple  conclusion is that something about differences in those 
areas is likely causal  in problems learning to read.


This is the difference between acquired dyslexia and  developmental 
dyslexia. I agree that, in general, linguistic stuff is  done in the same brain 
areas, roughly speaking, in most people (but not all  people). All I would 
question is how much that means in reality, the brain being  so very plastic and 
so much being general - available to learn stuff of any  kind.
 
If a brain learns a skill (knitting, reading, language, whatever) and there 
 is traumatic damage to that part of the brain which has done the learning 
then  the skill will be correspondingly damaged or even lost altogether, at 
least  temporarily. So acquired dyslexia, although horrible (and actually 
very  rare, at least in pure form) is not scientifically controversial. I 
accept  it, for example, without scientific quibble. The 'dyslexia' we all talk 
about is  developmental dyslexia where the unavoidable implication is  
either that there is a bit of brain, or a set of connections, or  something, 
genetically determined from the start, so innate, and pre-ordained to  do 
literacy and defective in some people or that there is some  underlying skill 
which is also thus innate and defective in some people. The  first is 
biologically impossible and the second (some general ability) has not  yet been 
reliably and consistently shown to be present in 'dyslexics'. I know  the present 
fashion (not quite consensus) is for defective phonological  awareness but 
a) I have, as you know, reservations as to what the research is  actually 
telling us and b) I am old enough to have seen other fashions come and  go! 
 
I have not kept up with all the recent research on thalamic or cortical  
indications, as there has been such a plethora of research citing  
'abnormalities' (if that's what they really are) in almost every part of the  brain 
anyone cares to look, and so much of it seems to me to be wildly  
over-interpreted and credulous. I know apparent differences have been found in  white 
matter density, composition or even, allegedly, connectivity, but I have  not 
read any which convinced me we were looking at anything real. Maybe I am  
contrary, but I am also sure, in compensation perhaps, that there is a deal  of 
credulous interpretation and much over-enthusiatic adoption and simplistic  
promotion of what the original neuroscientist researchers would, rather 
boringly  I agree, have been far more cautious about. But this is proper, if 
dull, in  my view.
 
One reference disputing the anomalous lateralisation foundation to  
Galaburda's work is:
 
Bryden, M.P., McManus, I.C.  & Bulman-Fleming, B. (1994) Evaluating the 
empirical support for the  Geschwind-Behan-Galaburda model of cerebral 
lateralisation. Brain &  Cognition. 26. 103-167.  
 
Pumfrey & Reason's 1991 book (specific learning difficulties  (dyslexia): 
challenges & responses) also debates the idea that histological  examination 
of the brain is able to tell us much about its behaviours.
 
There are more in the discussion in my chapter eight.
 
I think we will have to disagree about the validity of earlier, improperly  
defined, 'dyslexics'! To me it is clear, if the sample of 'dyslexics' 
studied  was not reliable, then the conclusions we can reach about them are 
equally  unreliable. Many 'facts' regarded as 'established' about 'dyslexics' 
were  actually about people who may well not have been 'dyslexic' as the 
discrepancy  criterion for diagnosis has been shown not reliably to indicate 
'dyslexia', or  anything neurological, at all. Studies made on subjects 
unreliably selected  are unreliable, and so, therefore, are their findings and their 
conclusions. And  I absolutely believe research should be interpreted 
cautiously! (As, indeed, I  believe extreme caution in respect of the climate 
would be very desirable, but  unlikely!) If there was a neurological basis to a 
disability called dyslexia (In  which, as you know, I do not believe) I do 
not think it would elude discovery  very easily, in view of the effort put 
into the search. The fact that we remain  about as far as ever from 
elucidation is a form of evidence in itself, I  think.
 
I am pleased we have been able to disagree with grace! Thank you for you  
thoughts.
 
 
Hugo


at: _http://www.hugokerr.info_ (http://www.hugokerr.info/) 

"We're here to help each other get  through this thing - whatever it might 
be." (Kurt Vonnegut) 
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