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
