The positronic brain was an extremely sophisticated computation device capable of artificial sentience, created by Dr. Noonian Soong, based on an idea from author Isaac Asimov. ( TNG : “ Datalore ”)

This device consisted of an artificial neural network, designed to imitate the humanoid brain. The construction of a positronic brain was extremely complex, and Dr. Soong was the only scientist to have done so successfully – on at least six occasions: two unspecified prototypes, B-4, Lore, Data, and Juliana Soong (although the latter three were the only truly stable units).

One of the difficulties in creating a stable positronic brain was determining how the electron resistance across the neural filaments was to be resolved. ( TNG : ” The Measure Of A Man ”)