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The Journal of Neurophysiology Vol. 83 No. 3 March 2000, pp. 1760-1763
Copyright ©2000 by the American Physiological Society
RAPID COMMUNICATION
Basal Gang, Centre National de la Recherche Scientifique Unité Mixte de Recherche 5543, Université Victor Segalen Bordeaux 2, 33076 Bordeaux Cedex, France
Boraud, T.,
E. Bezard,
B. Bioulac, and
C. E. Gross.
Ratio of Inhibited-to-Activated Pallidal Neurons Decreases
Dramatically During Passive Limb Movement in the MPTP-Treated
Monkey. J. Neurophysiol. 83: 1760-1763, 2000. Mink
advanced the hypothesis in 1996 that the role of the basal ganglia (BG)
is primarily one of focused selection; the encouragement of motor
mechanisms inducing a desired movement and the inhibition of competing
mechanisms. This would imply, in normal subjects, a ratio of
inhibited-to-activated (I/A) movement-related globus pallidus pars
internalis (GPi) neurons <1 and a drastic decrease of this ratio in
the parkinsonian state. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication should therefore decrease the specificity of the
response of this neuronal population. To test this working hypothesis
we studied the activity of GPi neurons in response to passive limb
movement in the normal and the parkinsonian monkey. Extracellular unit
recordings monitored any correlation between passive limb movements and
eventual modifications of the neuronal activity of the GPi in two calm,
awake, and drug naive monkeys (Macaca fascicularis)
before and after MPTP intoxication. In the normal animal, arm- and
leg-related neurons were located in clusters in the medial part of the
GPi. The I/A ratio was 0.22. Most GPi cells were linked to a single
joint. In the MPTP-treated monkey, the number of movement-related
neurons increased, the I/A ratio dropped significantly to 0.03, and
most responding cells were linked to several joints. These data, which
cannot be explained by the classic "box" model, endorse Mink's hypothesis.
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