In the early 1990s, researchers, including Itzhaki, found
evidence suggesting that as we age, the herpes virus begins
moving from its hideout near the bottom of the skull directly
into the brain (possibly because our immune systems lose some
bite). Indeed, one Journal of Pathology study found the virus in
a high proportion of postmortem brain samples taken from people
who'd died in their later decades, while it was absent in those
from people who'd died in youth or middle age. What effect does
the virus have when it reaches your brain? The short answer:
That depends. In certain people it seems to do much less damage
than in others; just as some of us never develop cold sores,
some of us can have the herpes virus inside our brains without
any horribly ill effects. But Itzhaki believes that in other
people—specifically those who carry APOE e4, a gene form, or
allele, strongly linked to Alzheimer's—the virus is not only
reactivated by triggers like stress or a weakened immune system,
but also actually begins to