Questions and Answers
Question # 30
Why do persons who exhibit symptoms of significant traumatic brain injury
(TBI) often present with a pattern of neuropsychological assets and deficits
that is suggestive of right cerebral hemisphere dysfunction?
Does this have any implications with respect to the presence or absence of
NLD in such persons?
As regards the first question, there are several reasons for this
finding, not all of which are mutually exclusive. Some of these
are as follows:
(1) There is a greater proportion of white/grey matter in the
right than in the left cerebral hemisphere (Goldberg & Costa,
1981). Hence, an event, such as significant TBI, that can cause
extensive neuronal stretching and shearing (and, in consequence,
some degree of damage and/or dysfunction of myelin), is likely to
cause much more disruption of systems within the right than of
those within the left cerebral hemisphere.
(2) Systems within the right hemisphere are inferred to be
principally responsible for intermodal integration and dealing
with novel information within a developmental context (Goldberg
& Costa, 1981; Rourke, 1982, 1987, 1988, 1989, 1995; Rourke,
van der Vlugt, & Rourke, 2002). Most psychological tests that
are thought to be "sensitive" to right hemisphere functioning
(or deficit) are more novel in nature (e.g., Wechsler Block
Design) than are those thought typically to reflect left
hemisphere functioning (e.g., Wechsler Vocabulary). The
latter (verbal) types of tests tend to be those that tap
into overlearned, rote, verbal information that is
"crystallized" to the point that it becomes somewhat
impervious to perturbations of general white matter
dysfunction. The systems within the right hemisphere
are not thought to be specialized for, or capable of,
this sort of intramodal functioning. Thus, if there
are general white matter perturbations as a result of
TBI, it is very likely that skills and abilities thought
to be mediated primarily by systems within the right
hemisphere will appear to be more impaired than are those
thought to be mediated primarily by systems within the left
hemisphere. This is, in one very important sense, the truth.
However, this "truth" is not a reflection of more damage within
the right hemisphere, but rather of more functional deficit of
the skills and abilities subserved primarily by systems within
the right hemisphere. In this sense, the basis for the exhibited
"lateralized" deficits is functional/physiological in nature and
does not necessarily imply more structural damage within the
right cerebral hemisphere.
(3) Obviously, significant TBI may be confined to the right cerebral
hemisphere. In such cases, one often sees the principal deficits as
very similar, or even identical, to deficits that are among those
considered to be primary in the NLD syndrome (see NLD Content and
Dynamics): outstanding visual-spatial-organizational deficits; and,
a predominance of somatosensory and psychomotor deficits on the left
side of the body.
(4) As outlined in Question #29, children
who exhibit the NLD syndrome (and, hence, may be suffering from
significant impairment of right hemisphere systems) are very likely
to "rush in where angels fear to tread," including out from between
parked cars and into roadways filled with speeding vehicles.
Similarly, they are more prone to fall from swings, slides, bicycles,
and so on than are children who are developing their psychomotor,
somatosensory, and visual-spatial-organizational skills at a normal
rate. Thus, it may be the case that some children who appear to be
suffering from greater impairment in skills and abilities thought
to be mediated primarily by systems within the right cerebral
hemisphere as a result of significant TBI were, in fact,
deficient in these skills and abilities prior to the TBI they
In answer to the second question, all of the points (1) through (4)
above, are relevant. More specifically, a decision regarding the
framing of an inference with respect to the presence or absence of
NLD prior to TBI involves a considered judgment regarding pre-TBI
neuropsychological and psychosocial dimensions. One feature of
particular interest regarding the framing of such an inference of
pre-TBI NLD is the very wide diversity of psychosocial outcomes
that are evident following TBI in both children (Butler, Rourke,
Fuerst, & Fisk, 1997; Hayman-Abello, Rourke, & Fuerst, 2003) and
adults (Warriner, Rourke, Velikonja, & Metham, 2003). One of these
psychosocial outcomes (internalized psychopathology) is seen most
frequently in persons with NLD (Casey, Rourke, & Picard, 1991;
Pelletier, Ahmad, & Rourke, 2001; Rourke, 2000; Tsatsanis, Fuerst,
& Rourke, 1997). But many post-TBI psychosocial outcomes are
completely normal and most abnormal outcomes are seen only rarely
in persons with NLD. These considerations have a number of
clinical ramifications, some of which are as follows.
Clinical Implications. For adolescents and young adults
who are thought to exhibit symptoms consistent with significant
TBI plus a pattern of neuropsychological assets and deficits that
would be consistent with NLD prior to their TBI, the bases for
a reasonable inference of pre-TBI NLD are at least three-fold.
Such persons usually present with the following: (1) a pattern
of post-TBI neuropsychological assets and deficits that is
concordant with NLD (with added features commonly seen in TBI);
(2) levels and patterns of academic performance (e.g., superior
single-word reading and spelling within a context of outstandingly
impaired mechanical arithmetic performance) very often seen in
persons with NLD; and, (3) a pre-TBI pattern of psychosocial
functioning (internalized psychopathology) that is typical of
persons at this age who have exhibited NLD for a very long period
of time. If such conditions obtain, it is reasonable to infer
the presence of a clinical comorbidity that a colleague of mine
is wont to characterize as "measles (i.e., NLD) and a broken leg
(i.e., TBI)." That said, it must be acknowledged that
determinations of this particular type of comorbidity are fraught
with difficulty, even for very experienced clinical neuropsychologists.
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