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10.4 Conclusion
This chapter has focused on two neural network models of voluntary movement
and proprioception under normal conditions. The models seek to explain detailed
electromyographic data of rapid single-joint arm movement and identify their neu-
ral substrates. The models were successful in providing answers to the questions
detailed in the previous sections as well as predicting several characteristics of vol-
untary movement:
The reciprocal and bidirectional neurons in primary motor cortex [19] are the
two partly independent cortical processes [30] for the reciprocal activation and
co-contraction of antagonist muscles in the control of joint rotation and joint
stiffness.
The origin of the triphasic pattern of muscle activation in normal conditions is
predicted to be cortical.
The neural substrates of the triphasic pattern of muscle activation in normal con-
ditions are predicted to be the neuronal discharge patterns of the reciprocal neu-
rons in primary motor cortex.
The afferent feedback from the muscle spindles to the cortex is responsible for
the generation of second agonist burst in the neuronal and EMG activities that
clamp the limb to its final position.
Many more predictions regarding voluntary movement control under normal con-
ditions can be found in [18,15,16,17]. In the next chapter, issues regarding voluntary
movement disorganization in Parkinson's disease will be addressed. In particular,
what role, if any, does dopamine depletion in key cortical and spinal cord sites play
in the initiation, execution, and control of voluntary movements in Parkinson's dis-
ease patients? Does dopamine depletion in basal ganglia, cortex, and spinal cord
have any effect on the triphasic pattern of muscle activation? How do the neuronal
and EMG variables change when dopamine is depleted?
References
1. Berardelli, A., Dick, J., Rothwell, J., Day, B., Marsden, C. Scaling of the size of the first
agonist EMG burst during rapid wrist movements in patients with Parkinson's disease. J Neu-
rol Neurosurg Psych 49 , 1273-1279 (1986)
2. Berardelli, A., Hallett, M., Rothwell, J., Agostino, R., Manfredi, M., Thompson, P.,
Marsden, C. Single-joint rapid arm movement in normal subjects and in patients with mo-
tor disorders. Brain 119 , 661-674 (1996)
3. Britton, T., Thompson, P., Day, B., Rothwell, J., Findley, L., Marsden, C. Rapid wrist move-
ments in patients with essential tremor. The critical role of the second agonist burst. Brain 117 ,
39-47 (1994)
4. Brown, S., Cooke, J. Initial agonist burst duration depends on movement amplitude. Exp Brain
Res 55 , 523-527 (1984)
5. Brown, S., Cooke, J. Movement related phasic muscle activation I. Relations with temporal
profile of movement. J Neurophys 63 (3), 455-464 (1990)
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