Memory cells (motor cortex)
- In a baseline epoch (no force field on the end effector), they have one preferred direction
- In a force perturbation epoch, they show a change in the preferred direction
- In a subsequent washout epoch (no force field on the end effector), the change in preferred direction persists.
For a quick review see 
- Motor control: Forcing neurons to change Current Biology, Volume 11, Issue 17, Pages R708-R709 A. Jackson, R. Lemon
- Li C-SR, Padoa-Schioppa C, Bizzi E: Neuronal correlates of motor performance and motor learning in the primary motor cortex of monkeys adapting to an external force field. Neuron 2001, 30:593-607.