Q; WHY left hemisphere language?

[Ruder Than You]

ljh at ecru.cc.utexas.edu wrote:
: It is true that in the overwhelming majority of right-handers, language is
: found in the left hemisphere. It is also true that when the left hemisphere
: is damaged, the right hemisphere probably participates in the recovery of
: language function. But there is serious question of how much the right
: hemisphere is capable of taking over language function. Some of the more
: dramatic evidence of its limitations in this respect comes from
: left hemispherectomies and commissurotomies. According to Marquardt 1982,
: "The immediate effect of a left hemispherectomy is to render the patient
: severely aphasic with auditory comprehension limited to perhaps only the
: ability to follow simple commands. Performance in comprehension appears
: to improve with time, but production is severely limited. Commissurotomized
: patients have been used to investigate capacities and functions of the right
: hemisphere. In general these split brain subjects never appear to develop
: language in the right hemisphere beyond the ability to carry out some simple
: commands and to recognize objects and assign names to them. These
: nonexpressive functions and some small amount of automatic speech, such as
: cursing and counting, are all that can confidently be attributed to the
: right hemisphere."

	For the most part, this is all true.  In most right-handed folks, 
the left hemisphere controls speech, and the same applies for about 70% of 
left handers.  
	The right hemisphere CAN take over control of the lost speech in 
some cases, but not in all.  Many patients with strokes aquire a global 
aspasia, often permanent.  Men in particular tend to not recover.  Woman 
have a much higer recovery rate from strokes than men, as they often have 
language not localized to either hemisphere, or are able to adapt more 
easily.  
	As you noted though, if the damage to the left hemiosphere is 
severe enough, there is certainly no assurance of recovery beyond simple 
speech. 

--
HISTORY, n.  An account mostly false, of events mostly unimportant, which 
are brought about by rulers mostly knaves, and soldiers mostly fools.
			_The Devil's Dictionary_
------------------------------------------------------------------------------
swallow at netaxs.com				  swallow at deeptht.armory.com