The Membrane Cooperativity Unit strives to understand how cellular plasma membranes work at very fundamental levels. For this purpose, the unit is dedicated to developing unique methodologies of single-molecule observation-manipulation in living cells and elucidating the mechanisms for the plasma membrane organization and function. This is enabled by cooperative interactions of molecules in/on the plasma membrane, with particular emphases on signal transduction and neuronal network formation, by extensively using single-molecule technologies.