Comparison of neuronal activities of external cuneate nucleus, spinocerebellar cortex and interpositus nucleus during passive movements of the rat's forelimb

Releasing dentate nucleus cells from Purkinje cell inhibition generates output from the cerebrocerebellum

The cerebellum generates its vast amount of output to the cerebral cortex through the dentate nucleus (DN) that is essential for precise limb movements in primates. Nuclear cells in DN generate burst activity prior to limb movement, and inactivation of DN results in cerebellar ataxia. The question is how DN cells become active under intensive inhibitory drive from Purkinje cells (PCs). There are two excitatory inputs to DN, mossy fiber and climbing fiber collaterals, but neither of them appears to have sufficient strength for generation of burst activity in DN. Therefore, we can assume two possible mechanisms: post-inhibitory rebound excitation and disinhibition. If rebound excitation works, phasic excitation of PCs and a concomitant inhibition of DN cells should precede the excitation of DN cells. On the other hand, if disinhibition plays a primary role, phasic suppression of PCs and activation of DN cells should be observed at the same timing. To examine these two hypotheses, we compared the activity patterns of PCs in the cerebrocerebellum and DN cells during step-tracking wrist movements in three Japanese monkeys. As a result, we found that the majority of wrist-movement-related PCs were suppressed prior to movement onset and the majority of wrist-movement-related DN cells showed concurrent burst activity without prior suppression. In a minority of PCs and DN cells, movement-related increases and decreases in activity, respectively, developed later. These activity patterns suggest that the initial burst activity in DN cells is generated by reduced inhibition from PCs, i.e., by disinhibition. Our results indicate that suppression of PCs, which has been considered secondary to facilitation, plays the primary role in generating outputs from DN. Our findings provide a new perspective on the mechanisms used by PCs to influence limb motor control and on the plastic changes that underlie motor learning in the cerebrocerebellum.

Consensus paper: current views on the role of cerebellar interpositus nucleus in movement control and emotion

In the present paper, we examine the role of the cerebellar interpositus nucleus (IN) in motor and non-motor domains. Recent findings are considered, and we share the following conclusions: IN as part of the olivo-cortico-nuclear microcircuit is involved in providing powerful timing signals important in coordinating limb movements; IN could participate in the timing and performance of ongoing conditioned responses rather than the generation and/or initiation of such responses; IN is involved in the control of reflexive and voluntary movements in a task- and effector system-dependent fashion, including hand movements and associated upper limb adjustments, for quick effective actions; IN develops internal models for dynamic interactions of the motor system with the external environment for anticipatory control of movement; and IN plays a significant role in the modulation of autonomic and emotional functions.

Representation of movement velocity in the rat's interpositus nucleus during passive forelimb movements

The interpositus nucleus (IN) receives a large amount of sensory information from the limbs and, in turn, elaborates signals for movement control. In this paper, we tried to gather evidence on the possibility that neurons in the IN may elaborate sensory representations of the forelimb kinematics and, particularly, of the movement velocity vector. For this purpose, the forepaw of anesthetized rats was attached to a computer-controlled robot arm displaced passively along two types of trajectories (circular and figure eight), with the limb joints unconstrained. The firing activity of single cells was recorded and related to limb position and the two components of the movement velocity vector, namely, movement speed and direction. By using multiple regression analysis, we found that 12 out of 85 (14%) neurons were modulated by position, 18 out of 85 (21%) neurons were modulated by direction, 24 out of 85 (28%) neurons were modulated by movement speed, and 31 out of 85 (37%) neurons were sensitive to the full movement velocity vector. Most of the neurons modulated only by the speed component of the velocity vector (19 out of 24) were located in the posterior portion of the IN, whereas neurons in the anterior portion were mostly related to both components of the velocity vector. These results suggest that sensory information related to whole-limb movement velocity may be encoded by the IN, indicating also that the posterior interpositus may preferentially represent movement speed.

Processing of limb kinematics in the interpositus nucleus

Neural representations of limb movement kinematic parameters are common among central nervous system structures involved in motor control, such as the interpositus nucleus of the cerebellum. Much experimental evidence indicates that neurons in the interpositus may encode limb kinematic parameters both during active, voluntary actions and during limb motion imposed passively, which entrains only sensory afferents. With respect to the sensory processing of information related to movement kinematics, we show that interpositus neuronal activity can parse out the directional from the scalar component (i.e., the movement speed) of the velocity vector. Moreover, a differential role for the anterior and posterior portion of interpositus in encoding these parameters emerged from these data, since the activity of the posterior interpositus was specifically associated to changes of movement speed. Limb movement representations in the interpositus nucleus may be instrumental for the control of goal-directed movements such as shaping hand during grasping or precise foot placement during gait. Finally, we discuss the idea that sensory information about the movement kinematics contribute to both feedback and anticipatory processes for limb movement control.