Involved in the development and/or maintenance of neuronal circuitry. Accessory subunit of the neuronal N-methyl-D-aspartate receptor (NMDAR) critical for maintaining the abundance of GRIN2A-containing NMDARs in the postsynaptic density. Regulates long-term NMDA receptor-dependent synaptic plasticity and cognition, at least in the context of spatial learning and memory. Interacts with PLZ domains of DLG2, DLG3 and DLG4 via its C-terminal TRV domain. Interacts with GRIN2A and GRIN2B via its CUB domains. Component of the postsynaptic density (PSD) of excitatory synapses. Expressed only in brain. Present throughout the central nervous system. Highly expressed in the hippocampal CA3 region, olfactory bulb and tubercle, caudate putamen, and neocortex in the adult brain. Observed restrictively in brain throughout embryonic and postnatal stages. Expression pattern in brain slightly changes from 13 dpc to postnatal day 21 (P21). Expressed in both cerebrum and cerebellum throughout P0 to P35. In the cerebrum expression reached a plateau at P14 while expression in the cerebellum remains constant throughout all postnatal stages. Depressed long-term potentiation (LTP) at Schaffer collateral-CA1 synapses, NMDAR-dependent spatial learning and memory. Rescued by the ampakine CX546 at physiological doses.