Movement-related potentials in Parkinson's disease. Presence and predictability of temporal and spatial cues.

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Movement-related potentials in Parkinson's
disease. Presence and predictability of temporal
and spatial cues. Cunnington R, Iansek R,
Bradshaw JL, Phillips JG. Brain. 1995 Aug118 (
Pt 4)935-50.
Introduction
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3-SMA is in close relation to Basal Ganglia (BG).
The function of SMA is disturbed in Parkinsons
Disease (PD), so PD patients have problems in
internally guided movements and their early MRP
is suppressed. Also PD patients show little
tendency to internalize the control of an
externally cued task, of which sequence can be
predicted because of its repetitive nature.
5-A controversy 1)When dealing with an
internally guided sequential movement, SMA and BG
are involved only in timing of sub-movements 2)
SMA and BG are involved in preparation and
processing of all the aspects of an internally
guided sequential movement such as timing and
movement direction, and target position.
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Experiment one
Methods
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End
1-EEG recorded from Cz, sampled 100 Hz, low
passed 20 Hz. Sweeps averaged from time 3 s to
1 s locked to each button release. Any sweep
exceeding 150 micro volt in peak to peak
amplitude was rejected as noisy. Each button was
held down for 4 seconds before moving as fast as
possible to the next button. patients were on
drug. 21 patients and 21 normal age-matched
subjects. 2-Internally cues versus externally
triggered cue absent versus cue present In the
former, people must pursue a memorized sequence
and keep each button depressed for almost 4
seconds according to their own timekeeping
system. In the latter, the path was illuminated
when it was gone through (spatial cueing). Each
button was extinguished extinguished 4 s after
the release of the previous button (temporal
cuing).
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Experiment one
The slope of MRPs following the peak is less
steep in PD than normals.
Results
10 micro volts
This is because the pathologic Basal Ganglia is
no longer able to terminate the activity of SMA
as described by Watts Mandir 1992.
Also eye movements were recorded and no MRP was
recorded correlated with eye movements.
The bars show the slop of MRPs between 1.5 s and
0.5 s before each movement. This is the time
window the early MRP is expected to be seen. As
you see no early ERP is seen in PD patients in
the cue present condition. Therefore, the rest of
analysis is focused just on cue absent condition
where both PD patients and normal subjects
exhibit SMA activity evident by early MRP. As
apparent in this figure, this MRP is less ample
in PD patients.
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Experiment three
We saw in experiment one that in PD patients,
presence of external cue turns off the SMA and
absence of external cue results in some activity
in SMA. The question here is that which aspect of
the cue does this? The information it offers
about the the spatial characteristics of the
movement or those about the temporal
characteristics of the movement? To approach this
Q, 16 PD patients were recruited in this
experimental setup
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Experiment three
Results
1-In this experimentin Parkinsonian patients, the
absence and presence of early MRP cprrelates with
presence and absence of temporal cueing and is
not correlate with that of spatial
cueing. 2-MRPs were not correlated with eye
movements. 3-In PD patients, the internal
control mechanisms operating via the
supplementory motor area are only involved when
no external timing cues are given and movements
must be internally timed.
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Experiment two
1-When externally cues are predictable, the
control of the movement will be governed by
internal predictory mechanisms. In this
experiment, predictability of external cues are
varied to see how the early component of MRP is
affected. 2-This predictability is varied for the
spatial cues and temporal cues distinctly to see
whether the SMA is involved in just the timing of
a movement or it is also involved in other
aspects of motor planning like the direction of
movement. 3-Ten normal subjects recruited.
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Experiment two
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Experiment four
To make sure that our results were really due to
activity in SMA the experiments 2 and 3 are
replicated in 3 normal subjects and 3 PD patients
with EEG recording from 9 sites on scalps. Most
potent waves were recorded in Cz over SMA.
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