It is a bidirectional connection between the GP and the subthalamic nucleus, including (1) fibers running from the GPe to the subthalamic nucleus, and (2) fibers running from the STN back to the GP.
^DeJong, Russell N.; Campbell, William; Haerer, Armin F. (2005). DeJong's the neurologic examination: incorporating the fundamentals of neuroanatomy and neurophysiology. Hagerstwon, MD: Lippincott Williams & Wilkins. p. 340. ISBN0-7817-2767-7.