We can see from common experience that mental faculties often deteriorate with age.  However, it is only relatively recently that imaging technology has allowed scientists to pinpoint the causes of this deterioration. It is becoming clear that there are multiple separate reasons for decline, ranging from Alzheimer’s Disease to more subtle physiological changes that build up over time. A study by UCLA researcher George Bartzokis, appearing this month in Neurobiology of Aging, identifies shrinking myelin sheaths as one of the reasons that at least some cognitive functions slow with age.

Myelin sheaths insulate neurons so that they can send signals quickly and efficiently. These sheaths constantly break down even in healthy humans, but we have regulatory systems to build them right back up again. Unfortunately, these systems often become less capable with time and the sheaths begin to break down. To explore the consequences of this, Dr. Bartzokis took MRIs of 72 subjects and then ranked them by the integrity of their myelin sheaths.

The second part of the experiment asked subjects to tap their fingers as quickly as possible, a classic test of neural processing speed. Dr. Bartzokis found that the slowest tappers were those with the least intact myelin sheaths. This discovery is valuable because it helps doctors distinguish between the various afflictions that can swamp the brain in old age. Now a painless MRI can determine whether noticeable slowdown is due to a serious disease or a more common process of wear-and-tear. Hopefully researchers will also be able to devise a method for keeping our myelin sheaths in good repair.