Neuropsychology Q&A
|
Questions &
answers on neuropsychological assessment
with Gordon I. Herz, PhD,
from the American Psychological
Association's Practice Directorate
online discussion forum,
Sunday, February 10, 2002, reprinted
with Dr. Herz's permission.
|
"No
matter how good the imaging methods become to
localize the lesion, they may
never tell us about HOW THE PERSON FUNCTIONS,
and the correlation with real world
behavior. This is nexus at which the
neuropsychologist functions."--Gordon Herz, PhD
Question:
"...I guess I still have a few doubts about
how precise the neuropsychological tests are
(other than as tests of functioning) or how
useful it is to try to name the specific areas
in
the brain which are associated with different
psychological functions. I mean, does it
really
help people to tell them that the problem is in
the front of their head or the back
of their
head or the middle of their head?"
Dr. Herz:
Great comments and question. Yes, I think it
could matter.
It could have implications for the disease
process, thus potentially predicting likely
prognosis
and useful treatments. For a basic example, if
cognitive deficits imply the 'front' part of the
brain but other cognitive functions (brain
areas) are spared, this might suggest a
'frontal'
dementia, as opposed to if 'deep brain'
functions are affected (i.e., motor, memory),
this might
suggest a Parkinson's type dementia. [Now you
are right, our testing methods might not be
this accurate yet, but this is improving all the
time]. Both of these entities have different
etiologies, may have no other 'objective test'
or biological markers to differentiate between
them, have different implications for the
patient, family, and treatment options, etc.
Unless of
course one takes the somewhat pessimistic view
that in the dementias the course is inevitably
downhill anyway, so what's the difference? As
suggested, sometimes the neuropsychological
testing provides a 'noninvasive' way that may
add to the 'soft signs' yielded, for example, by
a
neurological exam, even to the exquisitely good
localization offered by an imaging technique,
to help make the diagnosis.
This is an area of the literature I'm not too
familiar with, but I believe some of the
batteries of
neuropsychological tests are actually more
sensitive than other techniques currently
available
to detect, for example, Alzheimer's in its early
stages, but especially to help predict any
'subtypes' and classify with a certain
probability the likely rate of progression.
These could be
important to a patient and family.
Question:
"And if localization is so important (for
surgery perhaps), wouldn't more direct imaging
techniques, PET scans, etc. give better
accuracy?"
Dr. Herz:
Another excellent question. I was being trained
in neuropsychology about when CT was
replacing techniques such as
pneumoencephalograph, contrast-dye
injection-type procedures.
We always had hot debates about whether
increasingly good imaging would render
neuropsychology obsolete. This was not
unimportant to the neuropsychology graduate
student!
I don't worry about that any more.
Clinical neuropsychology is much more about
assessing FUNCTION, secondarily inferring from
that known brain locations, conditions,
processes if need be, thus as a diagnostic
procedure
when dx may not be known, but is much more
important in relating this to rehabilitation,
restoration, compensation for lost function in
real-world situations. In order to know that,
you
have to know about the neuro (cognitive)
(logical) conditions, and how your test results
relate
to those.
An example: An EARLY Alzheimer's patient, albeit
with measurable memory dysfunction and
exquisitely well-pinpointed loss of volume in
the hippocampus by MRI, may nevertheless be able
to operate a motor vehicle safely with
compensatory methods. No matter how good the
imaging
methods become to localize the lesion, they may
never tell us about HOW THE PERSON FUNCTIONS,
and the correlation with real world behavior.
This is nexus at which the neuropsychologist
functions.
Question:
"Of course, the tests that relate to driving
functions do seem to be quite useful, but these
are
just tests of functioning and don't require a
"neuro" label or location do they?"
Dr. Herz:
Well, I'll agree. There may not be anything in
particular about some tests that require the
'neuro-' label at the front of them.
Actually, I think about it the other way around.
ALL TESTS ARE NEUROPSYCHOLOGICAL. If you
think about it, just about any 'test' (by which
I mean a reproducible stimulus eliciting a
response) MUST BE a 'neuropsychological test' if
it filters through the CNS. About the only
thing I can think of that wouldn't be would be a
'knee-tap' test that filters only through at the
spinal cord level. A test can even be
'neuropsychological' if, for example, the
patient is
comatose or vegetative, i.e., 'evoked
potentials' tests that probe the pathway of
input all the
way to the cortex.
What makes a particular test
'neuropsychological' in my view is several
factors. At its best, a
test is neuropsychological if it is based on a
theory of human brain functioning, for example,
a
model that asserts important domains of
functioning include level of arousal,
information
processing, and planful responding. A test might
be constructed to tap one or more of these
domains.
Other features I would think are important to
label a test 'neuropsychological' might have to
do
with: its known relationship to brain
locations/systems; its known stability or change
in response
to various CNS conditions, and of course the
purpose for which the test is used. The use of
the
'neuro' label I think has much more to do with
the construction, purpose of administering, and
the interpretation of the instrument itself
than, necessarily, the test itself.
For example, think of the use of the WAIS-III as
a 'neurocognitive' test. Not initially designed
for a neuropsych purpose, but when correlated
with models of important cognitive domains
other than 'g' (look at the 'processing speed
index,' for example) with effects in individuals
with
known brain illness, etc, and when interpreted
in these contexts, the USE OF the instrument
may become 'neuropsychological.'
Gordon I. Herz, PhD
Private practice in neuropsychology
Madison, Wisconsin
