Opposite optimal current flow directions for induction of neuroplasticity and excitation threshold in the human motor cortex.

Background: Directional sensitivity is relevant for the excitability threshold of the human primary motor cortex, but its importance for externally induced plasticity is unknown.

Objective: To study the influence of current direction on two paradigms inducing neuroplasticity by repetitive transcranial magnetic stimulation (rTMS).

Methods: We studied short-lasting after-effects induced in the human primary motor cortex of 8 healthy subjects, using 5 Hz rTMS applied in six blocks of 200 pulses each, at 90% active motor threshold.