The Cooperative Neuron is part of a revolution that is occurring in the sciences of brain and mind. It explores the new field of cellular psychology, a field built upon the recent discovery that many neurons in the brain cooperate to seek agreement in deciding what's relevant in the current context. This cooperative context-sensitivity provides the cellular foundations for knowledge, doubt, imagination, self-development, and the search for purpose in life. This emerging field has far-reaching and fundamental implications for psychology, neuroscience, psychiatry, neurology, and the philosophy of mind.