Single cells were recorded in the magnocellular red nucleus (RNm) of two cynomolgus monkeys using tungsten microelectrodes. The first monkey was trained to press finger switches and to operate a push-pull device. Comparison of responses while operating the two devices demonstrated a strong distal bias. The finger device elicited large modulations in discharge (greater than or equal to 50 impulses/s) in 75% of the sampled neurons. Most cells fired optimally during thumb switch operation, but also fired vigorously in association with other switch operations. The left motor cortex was removed from the second monkey 18 months prior to microelectrode recording. Cells in the cortically denervated RNm discharged vigorously in association with grouped finger movements that opened and closed the affected right hand. These results coupled with our previous findings suggest that the RNm is preferentially linked to distal limb muscles, and the primary role of the forelimb zone may be to control coordinated hand function including grouped movements of the fingers.

Animals↗

PubMedDate not supplied

Distributed modular architectures linking basal ganglia, cerebellum, and cerebral cortex: their role in planning and controlling action.

The motor system includes structures distributed widely through the CNS, and in this feature article we present a scheme for how they might cooperate in the control of action. Distributed modules, which constitute the basic building blocks of our model, include recurrent loops connecting distant brain structures, as well as local circuitry that modulates loop activity. We consider interconnections among the basal ganglia, cerebellum, and cerebral cortex and the specialized properties of certain cell types within each of those structures, namely, striatal spiny neurons, cerebellar Purkinje cells, and neocortical pyramidal cells. In our model, striatal spiny neurons of the basal ganglia function in contextual pattern recognition under the training influence of reinforcement signals transmitted in dopamine fibers. Cerebellar Purkinje cells also function in pattern recognition, in their case to select and execute actions through training supervised by climbing fibers, which signal discoordination. Neocortical pyramidal cells perform collective computations learned through a local training mechanism and also function as information stores for other modular operations. We discuss how distributed modules might function in a parallel, cooperative manner to plan, modulate, and execute action.

Action Potentials↗

PubMedDate not supplied

Cerebellar guidance of premotor network development and sensorimotor learning.

Single unit and imaging studies have shown that the cerebellum is especially active during the acquisition phase of certain motor and cognitive tasks. These data are consistent with the hypothesis that particular sensorimotor procedures are acquired and stored in the cerebellar cortex and that this knowledge can then be exported to the cerebral cortex and premotor networks for more efficient execution. In this article we present a model to illustrate how the cerebellar cortex might guide the development of cortical-cerebellar network connections and how a similar mechanism operating in the adult could mediate the exportation of sensorimotor knowledge from the cerebellum to the motor cortex. The model consists of a three-layered recurrent network representing the cerebello-thalamocortical-ponto-cerebellar limb premotor network. The cerebellar cortex is not explicitly modeled. Our simulations show that Hebbian learning combined with weight normalization allows the emergence of reciprocal and modular structure in the limb premotor network. Reciprocal connections allow activity to reverberate around specific loops. Modularity organizes the connections into specific channels. Furthermore, we show that cerebellar learning can be exported to motor cortex through these modular and reciprocal premotor circuits. In particular, we simulate developmental alignment of visuomotor relations and their realignment as a consequence of prism exposure. The exportation of sensorimotor knowledge from the cerebellum to the motor cortex may allow faster and more efficient execution of learned motor responses.

Adult↗