A hyperencephalogram was a 23rd century medical analysis of brain-wave activity, measured as a brain circuitry pattern, or BCP. It may have been the natural descendant of the 20th century electroencephalogram, or EEG. The BCP was considered a unique characteristic for every individual, akin to fingerprints, making that individual's hyperencephalogram an important part of his or her medical record. An individual's hyperencephalogram could be altered if interfered with by another resident brain-wave activity, such as an invading telepathic or noncorporeal lifeform.
In 2269, Mira Romaine's hyperencephalogram was altered when she became possessed by invading Zetarians, and her brain circuitry pattern readout was instrumental in diagnosing this. (TOS: "The Lights of Zetar").