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In their study, Tremblay and colleagues [49] observed an abnormal oscillatory GPi
response, but failed to offer a functional role for it oscillatory responses. We propose
that such GPi oscillatory responses (repetitive GO signal), comprising of at least two
inhibitory-excitatory sequences, gate (multiply) the DV signal and generate repeti-
tive volitional motor commands (DVV signals; not shown), which in turn generate
repetitive agonist-antagonist muscle bursts (see row 2, column 3 of Figure 11.8)
needed sometimes by PD patients to complete the full amplitude of the movement.
11.8 Simulated Effects of Dopamine Depletion on EMG
Activities
As mentioned in the previous chapter, single ballistic movements at a joint in normal
individuals are made with a single biphasic (sometimes triphasic) pattern of EMG
activity in agonist and antagonist muscles [39, 4, 9, 10, 11, 35, 29, 30, 31, 53, 38].
In PD patients, the size of the first agonist burst is reduced. Up to a certain size,
movements might be performed by a single agonist-antagonist pattern of muscle ac-
tivation [26], but there are times that movements would require additional bursts of
EMG activity [37, 2, 23] in order for the limb to reach the target. The extended
DA-VITE-FLETE model has offered a plausible hypothesis of why PD EMG
agonist burst activity is reduced and why sometimes multiple bursts of AG-ANT-
N
ormal ca
s
e
PD case
0.1
0.1
0.08
0.08
0.06
0.06
0.04
0.04
0.02
0.02
0
0
0
50
100
150
0
50
100
150
4
4
3
3
2
2
1
1
0
0
0
50
100
150
0
50
100
150
Time
Time
Fig. 11.7: Comparison of simulated GO signals (row 1) and
-MN activities (row 2)
in normal (column 1) and dopamine-depleted (column 2) conditions. (Row 2)
Blue
solid curve
: agonist
α
-MN activity.
Note in PD case, the triphasic pattern is disrupted and it is replaced by a biphasic
pattern of muscle activation. Also, the peaks of agonist and antagonist bursts are
decreased.
α
-MN activity;
Red-dashed curve
: antagonist
α
