The brain scan device is a component of the DNA resequencer that was discovered in Anubis's underground laboratory on P3X-584. The small rectangular unit is self contained and is used to analyze a subject's current physiological status and to feed that information back into the DNA manipulator. Major Altman discovered the device, and it was brought back from the planet to monitor the evolution of Khalek, the hybrid prototype they had discovered in stasis on the planet.
The device aims four beams of green light at the subject's head and is able to provide a visual display of actual synaptic interaction in the brain in real time. The image on the monitor indicates areas in red where synaptic activity is maximized. A normal human brain would typically show about 5 to 10% coverage, however Khalek's brain was evolving before their eyes and increased from 68% coverage until it plateaued at 80%. Because it is theorized that 80 to 90% brain activity is required for conscious, willful ascension, the brain scan device was able to give an indication of Khalek's ability to ascend, and Mitchell coined the name "ascendometer" for the device.
Following Khalek's death, Carter continued to research the data collected by the brain scan device. Because the device can register and target certain areas of the brain being used for certain functions, it was possible to determine which portions of the brain were active when Khalek manifested the special telekinetic powers he had acquired due to his higher level of evolution. Using the theory that the Ori were affecting the Priors in much the same way, Carter and Dr. Lee were able to develop an anti-prior device that uses fluctuating ultrasonic frequencies to target and neutralize the higher brain functions of a Prior, thus inhibiting his special abilities.
Dr. Lam also used the brain scan device to monitor the brain activity of Orlin after he chose to retake human form as a child in an attempt to retain the knowledge of the Ancients to help find a cure for the Prior plague. His synaptic activity registered as a highly active scan, however the human brain isn't meant to hold that much information. The scan indicated that pockets of Orlin's brain cells were shutting down, as if wearing out from extremely unnatural overuse, and they eventually began dying because they couldn't handle the synaptic activity.
Cross Reference: Major Altman, Anti-Prior Device, Ascension, DNA Resequencer, Khalek, Orlin
Episode Reference: Prototype, The Fourth Horseman