Mark Lee Mayer is scientist emeritus at the National Institutes of Health (NIH). His research investigates glutamate receptor ion channels, the major mediators of excitatory synapses in the brain. He has made numerous observations that have changed our view of receptor function and neurotransmission in the brain. Major findings include discovery of the block of NMDA receptors by extracellular Mg and their high Ca permeability; analysis of the permeation and block of Ca permeable AMPA and kainate receptors by cytoplasmic polyamines; and structural studies on ligand binding, allosteric modulation, and gating using X-ray diffraction and cryoelectron microscopy.