Postsynaptic RAC1 GTPase activating protein (GAP) that plays a key role in neuronal morphogenesis and migration mainly during development of the cerebral cortex. Regulates excitatory and inhibitory synapse maturation and density in cortical pyramidal neurons. Mechanistically, acts by binding and deforming membranes, thereby regulating actin dynamics to regulate cell migration and differentiation. The F-BAR domain mediates oligomerization, binds membranes, and induces plasma membrane protrusions.