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This study examined whether lesions to the cerebellum obtained in early childhood are better compensated than lesions in middle childhood or adolescence. Since cerebellar lesions might affect motor as well a cognitive performance, posture, upper limb and working memory function were assessed in 22 patients after resection of a cerebellar tumour (age at surgery 1-17 years, minimum 3 years post-surgery). Working memory was only impaired in those patients who had received chemo- or radiation therapy. Postural sway was enhanced in 64% of the patients during dynamic posturography conditions, which relied heavily on vestibular input for equilibrium control. Upper limb function was generally less impaired, but 54% of the patients revealed prolonged deceleration times in an arm pointing task, which probably does not reflect a genuine cerebellar deficit but rather the patients' adopted strategy to avoid overshooting. Age at surgery, time since surgery or lesion volume were poor predictors of motor or cognitive recovery. Brain imaging analysis revealed that lesions of all eight patients with abnormal posture who did not receive chemo- and/or radiation therapy included the fastigial and interposed nuclei (NF and NI). In patients with normal posture, NI and NF were spared. In 11 out of 12 patients with abnormal deceleration time, the region with the highest overlap included the NI and NF and dorsomedial portions of the dentate nuclei in 10 out of 12 patients. We conclude that cerebellar damage inflicted at a young age is not necessarily better compensated. The lesion site is critical for motor recovery, and lesions affecting the deep cerebellar nuclei are not fully compensated at any developmental age in humans.

Background: Parkinson's disease is accompanied by deficits in passive motion and limb position sense., Objective: To investigate whether deep brain stimulation of the subthalamic nucleus (STN-DBS) reverses these proprioceptive deficits., Methods and Results: A passive movement task was applied to nine patients with Parkinson's disease and bilateral chronic STN-DBS and to seven controls. Thresholds for 75% correct responses were 0.9 degrees for controls, 2.5 degrees for Parkinson's disease patients when stimulation was OFF, and 2.0 degrees when stimulation was ON., Conclusions: STN-DBS improves kinaesthesic deficits in Parkinson's disease, but does not lead to a full recovery of proprioceptive function.

A coordinated movement is easy to recognize, but we know little about how it is achieved. In search of the neural basis of coordination, we present a model of spinocerebellar interactions in which the structure-functional organizing principle is a division of the cerebellum into discrete microcomplexes. Each microcomplex is the recipient of a specific motor error signal - that is, a signal that conveys information about an inappropriate movement. These signals are encoded by spinal reflex circuits and conveyed to the cerebellar cortex through climbing fibre afferents. This organization reveals salient features of cerebellar information processing, but also highlights the importance of systems level analysis for a fuller understanding of the neural mechanisms that underlie behaviour.

We investigated how humans with hereditary cerebellar degeneration [spinocerebellar ataxia (SCA) type 6 and 8, n = 9] and age- and sex-matched healthy controls (n = 9) adapted goal-directed arm movements to an unknown external force field. We tested whether learning could be generalized to untrained regions in the workspace, an aspect central to the idea of an internal model, and if any learning could be retained. After removal of the force field, SCA patients showed little or no learning-related aftereffects indicating that repeated force-field exposure never led to successful force compensation. In contrast, healthy control subjects quickly adapted their movements to the new force field. The difference in force adaptation was significant for movements to targets that required both the shoulder and elbow joint (P < 0.001). Moreover, the generalization of learned movements to targets outside the learned workspace was prevented by the cerebellar degeneration (P < 0.01). Retention of force adaptation was significantly lower in SCA patients (P = 0.003). The severity of ataxia in SCA patients correlated negatively with the extent of learning (r = -0.84, P = 0.004). Our findings imply that progressive loss of cerebellar function gradually impairs force adaptation. The failure to generalize learning suggests that cerebellar degeneration prevents the formation of an internal representation of the limb dynamics.

Precise knowledge about limb position and orientation is essential for the ability of the nervous system to plan and control voluntary movement. While it is well established that proprioceptive signals from peripheral receptors are necessary for sensing limb position and motion, it is less clear which supraspinal structures mediate the signals that ultimately lead to the conscious awareness of limb position (kinaesthesia). Recent functional imaging studies have revealed that the cerebellum, but not the basal ganglia, are involved in sensory processing of proprioceptive information induced by passive and active movements. Yet psychophysical studies have suggested a prominent role of the basal ganglia in kinaesthesia. This study addresses this apparent dichotomy by investigating the contributions of the cerebellum and the basal ganglia to the perception of limb position. Using a passive movement task, we examined the elbow position sense in patients with a dysfunction of the basal ganglia (Parkinson's disease, n = 9), patients with cerebellar degeneration [spinocerebellar ataxia (SCA) types 6 and 8, n = 6] and age-matched healthy control subjects (n = 11). In comparison with healthy control subjects, Parkinson's disease patients, but not SCA patients, were significantly impaired in the ability to detect displacements correctly. A 1 degrees forearm displacement was correctly recognized in >75% of trials by control subjects and SCA patients, but only in 55% of Parkinson's disease patients. Only at 6 degrees displacement did Parkinson's disease patients exhibit a response rate similar to those of the two other groups. Thresholds for 75% correct responses were 1.03 degrees for controls, 1.15 degrees for cerebellar patients and 2.10 degrees for Parkinson's disease patients. This kinaesthetic impairment significantly correlated with the severity of disease in Parkinson's disease patients, as determined by the Unified Parkinson's Disease Rating Scale (r = -0.7, P = 0.03) and duration of disease (r = -0.7, P = 0.05). In contrast, there was no significant correlation between performance and the daily levodopa equivalent dose. These results imply that an intact cerebro-basal ganglia loop is essential for awareness of limb position and suggest a selective role of the basal ganglia but not the cerebellum in kinaesthesia.

Accuracy and kinematics of horizontal arm pointing movements to visual targets were studied on three cosmonauts in 10-, 140-, and 172-d spaceflights in order to investigate mechanisms of the sensorimotor adaptation to microgravity. The Austrian equipment MONIMIR was mounted on board the Russian space station MIR and used for three-dimensional recording of the arm position and presentation of the targets. It was found that movement accuracy remained constant whereby movement durations significantly increased in all inflight sessions compared to the preflight baseline values. Inflight, movement peak velocities as well as acceleration and deceleration peak values decreased significantly. Analysis of the velocity-time profiles showed that the ratio between acceleration and deceleration phases decreased slightly for one cosmonaut and increased insignificantly for the other two cosmonauts. All phases of the acceleration-time profiles increased inflight by the same factor. These data fail to support the assumption of an increased role of the direct visual guidance in movement execution in microgravity. This suggests that the movement slowing in microgravity may be caused by a control strategy employed by the CNS to avoid the specific disadvantage of the absence of gravity. It is hypothesized that intra-movement control mechanisms play an important role in the movement coordination in the altered gravity environment.