Movement-Related Potentials in Parkinson

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Movement-Related Potentials in Parkinsons
DiseaseExternal Cues and Attentional
Strategies R. Cunnington, R. Iansek, J.L.
Bradshaw. Movement Disorders Vol. 14, No. 1,
1999, pp. 6368
Introduction
Hypokinetic movement can be greatly improved in
Parkinsons disease patients by the provision of
external cues to guide movement. It has recently
been reported, however, that movement performance
in parkinsonian patients can be similarly
improved in the absence of external cues by using
attentional strategies, whereby patients are
instructed to consciously attend to particular
aspects of the movement which would normally be
controlled automatically.
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Attentional strategy
External cues
the same improvement in movement performance was
also shown when external cues were removed and
patients were instructed to concentrate on
walking with the same large steps using
attentional strategies alone.
Providing horizontal lines set at an appropriate
stride length can greatly improve gait
performance.
Micrographia may be improved in Parkinsons
disease patients by providing continuous verbal
reminders to write big, thereby directing the
patients attention toward producing a large
amplitude.
Providing lines set at an appropriate stroke
amplitude can similarly improve micrographic
handwriting in parkinsonian patients.
Pooya As stated above, people are verbally
reminded to write big. Therefore it can be
equivalently assumed that people are being helped
in terms of their memory. I mean that this is not
an attentional strategy but it is a strategy to
help memory in those patients who have forgotten
what is the normal size of a hand-written text.
Here, I am referring to the dichotomy of
procedural/habit- learning and memory versus
declarative- learning and memory (see for example
Bayley et al 2005 Nature). We can say that the
size of hand-writing is a habit, that in PD
patients is forgotten, and giving verbal
instruction is an attempt to recruit compensate
declarative mechanisms.
!
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Methods
EEG recorded from Cz in 24 PD patients and 24
normal subjects. Patients were on medication.
Subjects performed a sequential button-pressing
task using a tapping board consisting of a box
containing two parallel rows of 10 buttons, one
above the other. Light-emitting diodes beneath
each button were initially illuminated along a
pathway consisting of a particular combination of
10 top- and bottom-row buttons. During
experimental trials, lights underneath the
buttons were progressively extinguished from
right to left.
Parkinsons disease and control subjects were
further divided into subgroups, with half
receiving explicit instruction to internally
generate responses and half receiving no such
instruction. No Instruction Subjects were given
the instruction Hold down each button until the
light underneath goes off, then move as quickly
as possible to press the next button in the
sequence. They were not given any instruction
regarding self-timing strategies.
With Instruction Subjects were given the same
initial instruction, and further instructed The
light will go off 4 sec after your previous
movement. Try to time the interval for yourself
and try to anticipate when the light will go off
so that when the light goes off you are ready to
move. Therefore, subjects were instructed to
internally generate responses rather than to rely
on external cues, although they were still
required not to move until the cue was given.
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Results Discussion
By some extra instruction offered to those PD
patients who are in instructed group the timing
and predictability of the stimulus was drawn
under their attention. The result shows that
attention can (at least partially) solve the
problems of PD patients and make their (reaction
times) RTs and (movement related potentials) MRPs
almost like normal people.
Pooya I can equivalently explain this effect by
considering the intellectual problems of PD
patients. And by intellectual problems I mean the
disability of PD patients to discover the
relations of successive events due to their
pseudodementia as a result of, say, depression..
PD patients in not instructed group could not
discover the regularity of GO signals so they
never could predict it and show predictory
activity in MRP. In contrast, normal people in
not instructed group, could discover that there
is a regularity in the GO signals and after a few
trials started to predict the occurrence upcoming
GO signals based on the regularity that they have
discovered on their own. PD patients in
instructed group do not have this problem
because the regularity has already been
explicitly described for them.
!
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Results Discussion
Movement duration was just affected by PD.
Receiving Instructions and hence attentional
strategies had no effect on movement duration.
Perhaps the reason for this latter effect, or I
had better say lack of effect, is that this
aspect of the task is not the one to which people
were attending.
Last point
In no instruction group, because of the regular
pattern of cues and responses, the task could be
considered a contingent negative variation
paradigm, with the previous response providing
the warning stimulus for the next cue and
response. On the other hand, when subjects are
instructed to concentrate on anticipating
presentation of the cue, movements are self-timed
(although not strictly self-paced) and may be
considered to reflect a Bereitschaftspotential
paradigm.
!
Pooya to how much extent you agree? Considering
the fact that the shape of MRPs (slide 4) are
identical in the two groups of normal subjects,
can they be considered as two different
identities?
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