The basal ganglia network mediates the planning of movement amplitude

Abstract

This study addresses the hypothesis that the basal ganglia (BG) are involved speci®cally in the planning of movement amplitude (or covariates). Although often advanced, based on observations that Parkinson's disease (PD) patients exhibit hypokinesia in the absence of signi®cant directional errors, this hypothesis has been challenged by a recent alternative, that parkinsonian hypometria could be caused by dysfunction of on-line feedback loops. To re-evaluate this issue, we conducted two successive experiments. In the ®rst experiment we assumed that if BG are involved in extent planning then PD patients (who exhibit a major dysfunction within the BG network) should exhibit a preserved ability to use a direction precue with respect to normals, but an impaired ability to use an amplitude precue. Results were compatible with this prediction. Because this evidence did not prove conclusively that the BG is involved in amplitude planning (functional de®cits are not restricted to the BG network in PD), a second experiment was conducted using positron emission tomography (PET). We hypothesized that if the BG is important for planning movement amplitude, a task requiring increased amplitude planning should produce increased activation in the BG network. In agreement with this prediction, we observed enhanced activation of BG structures under a precue condition that emphasized extent planning in comparison with conditions that emphasized direction planning or no planning. Considered together, our results are consistent with the idea that BG is directly involved in the planning of movement amplitude or of factors that covary with that parameter.

Neural Changes in Control Implementation of a Continuous Task

“…Notably absent from our imaging results was the activation of posterior parietal regions, which were previously shown to be involved in tracking errors (Krigolson and Holroyd, 2006) or making on-line corrections (Desmurget et al, 1999(Desmurget et al, , 2004a during continuous motor tasks. Given that in these studies the posterior parietal cortex was said to be implicated in a "low-level" type of control, the lack of activation in our case may indicate that subjects used a higher-level type of control based on prefrontal regions.…”

Reorganization of Finger Coordination Patterns During Adaptation to Rotation and Scaling of a Newly Learned Sensorimotor Transformation

“…In contrast, Krakauer et al (2004) found that adaptations to changes in visuomotor gain induced only a subtle increase in rCBF signal in a subset of subcortical motor areas activated in their control task (left insula/putamen, left medial cerebellum, and right putamen) and no significant activation outside of the regions active during the control task. These results are consistent with the proposed role of basal ganglia in scaling the magnitude and rate of increase of muscle activity during movement (Horak and Anderson 1984) and thus in controlling movement extent and velocity (Anderson and Horak 1985;Desmurget et al 2003Desmurget et al , 2004Mazzoni et al 2007;Turner and Anderson 1997;Turner et al 2003). Indeed, inactivation of basal ganglia output pathways in animal models reduces the extent of goal-directed movements but alters neither reaction times (Mink and Thach 1991) nor the normal activation sequence seen during reaching prior to inactivation (Horak and Anderson 1984).…”

Untitled

“…The faulty proprioceptive feedback available caused smaller steps relative to healthy participants because visual confirmation was not available to compensate for the diminished external cueing. Smaller movement amplitude was also noted by Desmurget et al [16], when proprioception was primary source of feedback available to individuals with PD when pointing towards a target, indicating that vision of the limb is required to improve target accuracy.…”