Signaling adapter that couples activated growth factor receptors to signaling pathway in neurons. Involved in the signal transduction pathways of neurotrophin-activated Trk receptors in cortical neurons (By similarity). Interacts with the Trk receptors in a phosphotyrosine-dependent manner and MEGF12. Once activated, binds to GRB2 (By similarity). The PID domain mediates binding to the TrkA receptor. Phosphorylated on tyrosine by the Trk receptors.