Corticospinal, rubrospinal and rubro-olivary projections: a unifying hypothesis.

There has been a dispute about the corticospinal and rubrospinal tracts for about 100 years. Both are descending motor pathways and have remarkably similar functional properties. It has been proposed previously that each system is primarily active in different movement contexts. The corticospinal tract is most involved when a new movements is being learnt, while the rubrospinal tract is preferentially active when automated movements are being executed. However, what structure decides which system should be in use? In this article Philip Kennedy discusses the evidence that the rubro-olivary tract switches between the two systems depending on the context of the movement.