Motor primitives in vertebrates and invertebrates. Flash, Hochner. Current Opinion in Neurobiology 2005.

1. Idea that “The entire motor repertoire can be spanned by applying a well-defined set of operations and transformations to these [motor] primitives… according to well-defined syntactic rules.”
2. “… new experimental, computational, and conceptual approaches are needed to further advance our understanding of motor compositionality.”
3. Many motor tasks can be accomplished many different ways, but the curse of dimensionality is reduced because there is an assumption that “there is a limited vocabulary of primitives.”
4. Paper considers:
   1. How are motor and movement primitives defined
   2. What is the nature of primitives and how are they represented
   3. What are the rules related to generation of large repertoire of movements from a small set of elements
5. Paper by Chad Jenkins outlines some methods used to find motor primitives, include PCA, HMM, Isomap
6. Reaching motions follow stereotyped rules (straight lines with bell-shaped velocity profiles)
7. “… hand trajectory can be composed of a few velocity primitives, all with similar shapes characterized by a minimum-jerk […] or log-normal function […]. When stroke patients gain better control over their limb, the number of submovements decreases and their temporal overlap increases, giving smoother trajectories […]” Also babies similar
8. Grasping tasks.  “Finger movements and forces have been decomposed into basic synergies based either on the idea of uncontrolled manifold […] or on inverse dynamics computations […]. Complicated hand gestures, such as
   typing and finger spelling […], also consist of primitives or more complicated sequences that can be decomposed
   into a series of elementary units of action.”
9. “In monkey cortex, electrical microstimulation in primary motor and premotor cortex evokes complex purposeful movements involving many joints and even several body parts […]”
10. Not all possible combinations of primitives are used; the way they are put together defines on a syntax