Projection of forelimb group I muscle afferents to the cat cerebral cortex

Olov Oscarsson (1931-1996) of Lund University, a Pioneer in Cerebellar Neurobiology

The present Cerebellar Classic highlights the experimental work of the Swedish neurophysiologist Olov Oscarsson (1931-1996) on the afferent innervation of the cerebellum by axons emanating from neurons in the spinal cord and the inferior olive. Historically, the schemes of cerebellar division had been principally based on the external morphology of lobules and fissures. However, the macroscopic anatomical division of the cerebellum does not coincide with its pattern of functional organization. By defining a system of longitudinal somatotopy, Oscarsson contributed to the much needed plan of cerebellar division that correlates experimental information on axonal connections with physiology. His contribution has ultimately led to the currently accepted microzonal modular scheme of cerebellar corticonuclear microcomplexes.

A robot-aided visuo-motor training that improves proprioception and spatial accuracy of untrained movement

Proprioceptive function can become enhanced during motor learning. Yet, we have incomplete knowledge to what extent proprioceptive function is trainable and how a training that enhances proprioception may influence performance in untrained motor skills. To address this knowledge gap, healthy young adults (N = 14) trained in a visuomotor task that required learners to make increasingly accurate wrist movements. Using a robotic exoskeleton coupled with a virtual visual environment, participants tilted a virtual table through continuous wrist flexion/extension movements with the goal to position a rolling ball on table into a target. With learning progress, the level of difficulty increased by altering the virtual ball mechanics and the gain between joint movement and ball velocity. Before and after training, wrist position sense acuity and spatial movement accuracy in an untrained, discrete wrist-pointing task was assessed using the same robot. All participants showed evidence of proprioceptive-motor learning. Mean position sense discrimination threshold improved by 34%. Wrist movement accuracy in the untrained pointing task improved by 27% in 13/14 participants. This demonstrates that a short sensorimotor training challenging proprioception can a) effectively enhance proprioceptive acuity and b) improve the accuracy of untrained movement. These findings provide a scientific basis for applying such somatosensory-based motor training to clinical populations with known proprioceptive dysfunction to enhance sensorimotor performance.

Cerebellar dyssynergia in humans--a quantitative analysis

Patients with cerebellar lesions and limb ataxia performed two types of continuous tracking tasks involving flexion and extension of the index finger. In both tasks, patients were provided cutaneous and proprioceptive cues, but visual feedback was given in the first task (visual tracking) and not in the second (arbitrarily termed proprioceptive tracking). Raw records and Fourier-analyzed power spectra were compared with results in normal controls. Harmonic distortion was determined for each task. In all patients, as well as normal subjects, tracking performance was markedly improved and harmonic distortion substantially reduced during proprioceptive tracking. This surprising finding may result from a much shorter feedback loop for proprioceptive stimuli compared to visual stimuli. The tracking records, power spectra analysis, and determination of harmonic distortion provide both qualitative and quantitative data in patients with dyssynergia.

Physiological basis of cerebellar dysmetria

A primary control system for the arm position is formulated. The hypothesis that the cerebellum is a part of the system controller is checked by studying the nerve cells responses in the cerebellum, and motor cortex, to natural activation of muscular receptors. The results show that the cerebellum receives feedback information related to the speed of these receptors. The discussion concentrates on how the interruption of this feedback may result in excessive oscillations to instability. These observations are the base for evaluating how the cerebral lesions produce dismeasurements.

Vestibular and somatosensory inflow to the vestibular projection area in the post cruciate dimple region of the cat cerebral cortex

In anesthetized cats 251 cells within the cortical vestibular projection area, adjacent to the post-cruciate dimple, were analyzed as to their input characteristics employing extracellular recording techniques. The post cruciate dimple vestibular field, which is located in area 3a, has a high degree of convergence between vestibular and peripheral somatosensory input. The latter is not restricted to muscle afferents but includes cutaneous modalities. The functional significance of this vestibular cortical projection field is discussed.