The lateral reticular nucleus: a precerebellar centre providing the cerebellum with overview and integration of motor functions at systems level. A new hypothesis

Abstract

The lateral reticular nucleus (LRN) is a major precerebellar centre of mossy fibre information to the cerebellum from the spinal cord that is distinct from the direct spinocerebellar paths. The LRN has traditionally been considered to provide the cerebellum with segregated information from several spinal systems controlling posture, reaching, grasping, locomotion, scratching and respiration. However, results are presented that show extensive convergence on a majority of LRN neurons from spinal systems. We propose a new hypothesis suggesting that the LRN may use extensive convergence from the different input systems to provide overview and integration of linked motor components to the cerebellum. This integrated information is sent in parallel with the segregated information from the individual systems to the cerebellum that finally may compare the activity and make necessary adjustments of various motor behaviours.

Figure 1. The lateral reticular nucleus (LRN): a precerebellar nucleus that provides cerebellar circuits with an overview and integration of systems-level motor functions

A new physiological hypothesis is proposed for the LRN. The old concept of segregated inputs and outputs, respectively, to and from the LRN is indicated by black lines, and the new hypothesis proposing comparison across systems is shown in red. For simplicity, the behaviour is limited to posture, reaching, grasping and jaw opening, but does include other components such as eye and head movements. It is assumed that these different motor components are closely linked and need to be coordinated. Information about each motor component is signalled by distinct systems to the LRN: the bVFRT, C3–C4 PN, iFT and DF–trigeminal systems. There is extensive convergence between all of these systems, including excitation and inhibition to the LRN, but for clarity, only subsets of the diverging and converging paths are shown. The multiple convergence is simplified schematically by the combined red synapses to LRN neurons. The panels showing behaviour are from fig. 3 in Alstermark and Isa (; reproduced with permission of the Annual Review Organisation).