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. 2008;7(4):583-8.
doi: 10.1007/s12311-008-0059-3.

Cerebellum Predicts the Future Motor State

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Free PMC article

Cerebellum Predicts the Future Motor State

Timothy J Ebner et al. Cerebellum. .
Free PMC article

Abstract

Feed forward control and estimates of the future state of the motor system are critical for fast and coordinated movements. One framework for generating these predictive signals is based on the central nervous system implementing internal models. Internal models provide for representations of the input-output properties of the motor apparatus or their inverses. It has been widely hypothesized that the cerebellum acquires and stores internal models of the motor apparatus. The results of psychophysical, functional imaging and transcranial magnetic stimulation studies in normal subjects support this hypothesis. Also, the deficits in patients with cerebellar dysfunction can be attributed to a failure of predictive feed forward control and/or to accurately estimate the consequences of motor commands. Furthermore, the computation performed by the cerebellar-like electrosensory lobes in several groups of fishes is to predict the sensory consequences of motor commands. However, only a few electrophysiological investigations have directly tested whether neurons in the cerebellar cortex have the requisite signals compatible with either an inverse or forward internal model. Our studies in the monkey performing manual pursuit tracking demonstrate that the simple spike discharge of Purkinje cells does not have the dynamics-related signals required to be the output of an inverse dynamics model. However, Purkinje cell firing has several of the characteristics of a forward internal model of the arm. A synthesis of the evidence suggests that the cerebellum is involved in integrating the current state of the motor system with internally generated motor commands to predict the future state.

Figures

Fig. 1
Fig. 1
a Schematic of monkey performing the circular tracking task and the hand paths under varying viscous loads and the null force field. b Viscous (left column) and elastic (right column) force fields have distinct hand force profiles with the former being a function of tracking direction. c Muscle EMG activities follow the external forces. d Purkinje cell simple spike discharge, while modulated by the task kinematics, is not altered by the task dynamics (i.e., type and strength of the external force fields); from [32], with permission
Fig. 2
Fig. 2
a Schematic of the forward model prediction in Purkinje cells. State of the arm at time t+τ is predicted based of the state of the arm at time t and the motor command. b Simple spike firing during the Track period of the task is modeled and the same parameters are used to predict the firing during the entire task, including the Intercept period. The τ was estimated from the best regression fit achieved by shifting the firing and kinematic parameters relative to each other over −200 to +200 ms. c Example of the predicted simple spike discharge for medium target speed (5.7 cm/s), for both cw and ccw tracking at a start angle of 270°. d Distribution of delays between simple spike discharge and kinematics. The majority of cells have a negative delay indicating the change in firing preceded the change in kinematics; from [35], with permission

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