NMDAR, or N-methyl-D-aspartate receptor, is a type of receptor in the brain that plays a crucial role in synaptic plasticity, which is essential for learning and memory. It is a subtype of glutamate receptor and is activated when the neurotransmitter glutamate binds to it, allowing calcium ions to flow into the neuron. This process is vital for various brain functions. NMDAR is unique because it requires both glutamate and a change in voltage across the cell membrane to activate. This dual requirement makes it important for regulating neuronal communication and preventing excessive excitation, which can lead to conditions like epilepsy or neurodegenerative diseases.