Such a process would express itself in a presynaptic inhibition acting at the level of muscular afferents to motoneurons, thereby decreasing the reactivity of the spinal reflex pathways. However, it is probably incorrect to label it as exclusively spinal, since it may well reflect the action of a more general sensory input filtering mechanism intervening whenever a motor action is to be performed (cf. for instance Demairé, Honoré, & Conquery, in this volume).
First, at the highest level where a motor action is presumably defined in term of its "goal" or "intention" only, before any movement parameterization, it has been shown that preparation may be manipulated by experimentally controlling the probability of the required action. The functional state of neuronal pools in the precentral motor cortex, presumed to be influenced by activity in the associative cortical areas, was found to be sensitive to these experimentally induced changes in the level of preparation.
Later, during the second programming stage in which movement is presumably parameterized to become a spatially oriented action, prior information re