- You may be looking for Fal-tor-pan.
The disease caused the neuropeptide levels in the brain to decrease, and affected the logic capabilities. The treatment could only be performed by a Vulcan who was compatible with the patient, which usually meant a blood relative.
In 2378, Tuvok required fal-tor-voh as he began showing symptoms of the disease. However, the only other Vulcan on USS Voyager, Vorik, was not compatible, and he required a relative in the Alpha Quadrant.
In the original timeline, where Voyager spent twenty-three years in the Delta Quadrant, he returned home far too late for the treatment, and by 2404, Tuvok's mind had suffered irreparable damage, leading him to be permanently quartered in a mental hospital. (VOY: "Endgame")