Robo31 Is an Alternative Splice Form of Robo3 That Blocks

Robo3.1 is an alternative splice form of Robo3 that blocks the reception of Slit signals by the Robo1 and Robo2 receptors. Considering the guidance of commissural neurons crossing the ventral midline in the embryonic spinal cord of a vertebrate, would you expect Robo3.1 activity to increase (I) or decrease (D) as the growth cone crosses the midline? Write down I or D as your answer.