The brain consists of two hemispheres each responsible for controlling the opposite side of the body. Normally, each hemisphere inhibits the opposite side to avoid mirror movements (both sides performing same movement simultaneously).
After a stroke, the two hemispheres experience an unbalancing of both sides with the unaffected hemisphere receiving more signals than the affected hemisphere. This imbalance leads to increased excitability and decreased inhibition to the healthy side.
Priming is a technique used to enhance the brain’s ability to re-balance the two hemispheres following a stroke. Priming interventions include invasive and non-invasive techniques and can be administered prior to or during recovery.
Source: What is Cortical Priming?