Basal ganglia network mediates the control of movement amplitude.
Experimental Brain Research. 2003-11-01; 153(2): 197-209
DOI: 10.1007/s00221-003-1593-3
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https://www.bordeaux-neurocampus.fr/12298
1. Exp Brain Res. 2003 Nov;153(2):197-209. doi: 10.1007/s00221-003-1593-3. Epub
2003 Sep 6.
Basal ganglia network mediates the control of movement amplitude.
Desmurget M(1), Grafton ST, Vindras P, Gréa H, Turner RS.
Author information:
(1)Space and Action, INSERM U534, 16 av. du Doyen Lepine, 69500 Bron, France.
In the present study we address the hypothesis that the basal ganglia are
specifically involved in the planning of movement amplitude (or related
covariates). This prediction has often been put forward based on the observation
that Parkinson’s disease (PD) patients exhibit hypokinesia. A close examination
of the literature shows, however, that this commonly reported clinical symptom
is not consistently echoed by experimental observations. When required to point
to visual targets in the absence of vision of the moving limb, PD subjects
exhibit various patterns of inaccuracy, including hypometria, hypermetria,
systematic direction bias, or direction-dependent errors. They have even been
shown to be as accurate as healthy, age-matched subjects. The main aim of the
current study is to address the origin of these inconsistencies. To this end, we
required nine patients presenting with advanced PD and 15 age-matched control
subjects to perform planar reaching movements to visual targets. Eight targets
were presented in equally spaced directions around a circle centered on the
hand’s starting location. Based on a previously validated parsing procedure,
end-point errors were segmented into localization and planning errors.
Localization errors refer to the existence of systematic biases in the
estimation of the initial hand location. These biases can potentially transform
a simple pattern of pure amplitude errors into a complex pattern involving both
amplitude and direction errors. Results indicated that localization errors were
different in the PD patients and the control subjects. This is not surprising
knowing both that proprioception is altered in PD patients and that the ability
to locate the hand at rest relies mainly on the proprioceptive sense, even when
vision is available. Unlike normal subjects, localization errors in PD were
idiosyncratic, lacking a consistent pattern across subjects. When the
confounding effect of initial hand localization errors was canceled, we found
that end-point errors were only due to the implementation of an underscaled
movement gain (15%), without direction bias. Interestingly, the level of
undershoot was found to increase with the severity of the disease (inferred from
the Unified Parkinson’s Disease Rating Scale, UPDRS, motor score). We also
observed that movement variability was amplified (32%), but only along the main
movement axis (extent variability). Direction variability was not significantly
different in the patient population and the control group. When considered
together, these results support the idea that the basal ganglia are specifically
involved in the control of movement amplitude (or of some covariates). We
propose that this structure participates in extent planning by modulating
cortical activity and/or the tuning of the spinal interneuronal circuits.
DOI: 10.1007/s00221-003-1593-3
PMID: 13680045 [Indexed for MEDLINE]