Neurochemistry, or brain chemistry, was a medical science that dealt with the chemical makeup of an organic brain.
The breakdown of neurochemical molecules during transport was the cause of Transporter psychosis. (TNG: "Realm of Fear")
In 2154 Phlox routinely monitored Jonathan Archer's neurochemistry, while Archer was in stasis. (ENT: "Doctor's Orders")
In 2364 the effects of his time experiments affected Paul Manheim's neurochemistry, eventually contributing to his death. (TNG: "We'll Always Have Paris")
In 2370 Data stated, that while the Human brain could be described as cellular functions and neurochemical interactions, this could not explain Human consciousness. (TNG: "Emergence")
By the same year advancements in neurochemistry enabled Julian Bashir to successfully utilize neuromuscular adaptation. (DS9: "Melora")
In 2372, after Lieutenant Commander Tuvok conducted a mind meld with Ensign Lon Suder, The Doctor diagnosed him with a neurochemical imbalance in his mesiofrontal cortex, causing his erratic, violent behavior. (VOY: "Meld")
In 2373, after forcefully attempting to telepathically mate with Lt. jg B'Elanna Torres, Ensign Vorik was diagnosed with a neurochemical imbalance by The Doctor. The Doctor understood this meant Vorik was entering into pon farr. (VOY: "Blood Fever")