are still able to differentiate between degrees in spatial uncertainty, which indicates preservation of prediction mechanisms. In any case a systematic approach to this problem would involve analysis of learning evolution and variations of S- R compatibility. Second, no obvious disorganization of the programming stage was observed after DN exclusion but the inability to finely tune velocity and to use spatial maps appropriately were missing. Although part of the motor impairment observed during the execution phase may be related to a defective control of the ongoing movement, the data obtained in these experiments suggest incorrect velocity programming and erroneous spatial specification of the limb trajectory. A third hypothesis may be put forward according to which the neocerebellum participates directly in increasing the efficiency of motor control. In this connection, attention must be paid to postural reorganization preceding the execution of movement. It has been suggested that the development of the neocerebellum in primates might be related to the need for new posturo-kinetic patterns ( Massion & Sasaki, 1979). The DN could be directly involved through subcortical influences ( Schultz et al., 1979) in the control of axial and proximal muscles responsible for postural changes preceding the initiation of limb movement. The specificity of such a postural setting, which could increase the ac7 cessibility of central command to motor systems ( Requin, 1980), has still however to be tested.
This work was partly supported by CNRS grant (ATP Neurobiologie du système nerveux central) and INSERM grant (PRC Santé mentale et cerveau).
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