I stated in a previous post that the claim that children recover
better from brain injury than adults (the so-called "Kennard
principle") may be a myth. One private post I received asked me
to support my statement. One is good enough for me.
First, some weasel words. I said "may". Also, I haven't kept
up-to-date on this literature. Finally, my interest has always
been restricted to the recovery of language after brain damage,
although I believe that's where most of the data is anyway.
I then ransacked my file. In chronological order, and mostly
omitting references in the quoted sources:
>From St. James-Roberts (1981):
After noting considerable confusion in when the presumed
plasticity in the young ends (is it 12 months, 17 months, 5
years, 10 years, 12, years, or 15 years?), he says:
"In spite of this confusion, the principle of referential
recovery in the young brain due to plasticity has become part of
neuropsychological dogma, and is still widely and uncritically
cited." Still is [I say]
He then says:
"A number of human studies...have also failed to find age
differences in recovery, have obtained better recovery than
predicted by the plasticity hypothesis in adult-damaged patients,
or poorer than predicted recovery in child-damaged ones...Dennis
and Whitaker (1977)...have been unable to find convincing
evidence of hemisphere equipotentiality in the young brain.
[Other studies] have also generated results incompatible with
the traditional interpretation."
He then carries out his own massive review of the literature on
early and late hemispherectomy, and concludes: "It appears that
the evidence provided by the studies presumed to support the
plasticity hypothesis, like the overall evidence examined here,
is principally characterized by its shortcomings". The abstract
states "The findings fail to support the presuppositions of the
plasticity model".
Fletcher & Satz (1983) defend their earlier paper (Satz &
Fletcher, 1981), against criticism. The earlier paper, which I
don't have, apparently argued against the claim of better
recovery in the young. They say about the assumption of
plasticity "This assumption, which Issacson labeled a "myth",
was based on earlier animal studies (e.g. Kennard, 1936) that
have not been replicated". Turning to human studies, they say
"Most of the studied reviewed...failed to reveal better recovery
in children".
Finally, Piacentini & Hynd (1988), say: "the evidence fails to
support the idea that age at neurological insult is related to
sequelae of the damage or to the rate or degree of recovery.
Therefore, the use of age at insult as a predictive variable
regarding prognosis appears to be unwarranted, and it cannot be
assumed that recovery from brain damage occurring at an early age
will necessarily be more complete or rapid than that resulting
from damage with a later onset".
And, as an example of a textbook which appears to recognize that
there is some degree of controversy on the plasticity issue, I
offer Kalat (2001, p. 144): "The problem with the Kennard
principle is that it does not apply to all cases. The effects of
early brain damage may be greater than, less than, or the same as
the effects of later damage depending on the location of the
damage and the tested behavior. In some cases...infants suffer
far more severe consequences than adults."
Another example of a textbook recognition of this is Shaffer
(1999, p,. 360) where he says "later research has challenged
Lenneberg's ...notion that young children are more likely than
adolescents or adults to recover from traumatic aphasia".
Unfortunately, Shaffer contradicts himself earlier in the text
(p. 159) by stating that for brain damage in adolescents and
adults, "their recoveries are rarely as rapid or complete as
those of younger children. So the remarkable recuperative power
of the human brain (that is, plasticity) is greatest early in
life".
But this should do it for "may".
-Stephen
References in any old order:
Shaffer, D. (1999). Developmental psychology, 5th ed.
Kalat, J. (2001). Biological psychology, 7th ed.
Piacentini, J., & Hynd, G. (1988). Language after dominant
hemispherectomy: are plasticity of function and
equipotentiality viable concepts? Clinical Psychology
Review, 8, 595-609.
Hahn, W. (1987). Cerebral lateralization of function: from
infancy through childhood. Psychological Bulletin, 101,
376--
Fletcher, J., & Satz, P. (1983). Age, plasticity and
equipotentiality: a reply to Smith. J. Consult Clin.
Psychol. 51, 763--
St. James-Roberts, I. (1981). A reinterpretation of
hemispherectomy data without functional plasticity
of the brain. Brain and language, 13, 31-53.
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Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470
Department of Psychology fax: (819) 822-9661
Bishop's University e-mail: [EMAIL PROTECTED]
Lennoxville, QC
J1M 1Z7
Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy
Check out TIPS listserv for teachers of psychology at:
http://www.frostburg.edu/dept/psyc/southerly/tips/
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