The earliest trigger of Alzheimer's disease may be traffic jams occurring on the brain's cellular highways.

Researchers at the University of California at San Diego who led a multi-institutional study have found that prior to the formation of the destructive plaques that cause Alzheimer's, cellular debris accumulates along axons, whose long, thin fibers shuttle chemicals from neuron to neuron and from one brain neighborhood to the next. Clogging these transportation routes promotes the generation of plaque.

“It's choking up supply lines,” says Lawrence S. B. Goldstein, professor of cellular and molecular medicine at the university. “It's like a rock in a garden hose. The chemicals can’t get through to do their job.” By studying mice with the condition and the brains of people who died during early stages of Alzheimer's, the scientists found that the more debris that exists on an axon highway, the harder that region is eventually hit with plaque.

In Alzheimer's, brain proteins called amyloid and tau are present in abnormal amounts, but researchers have long debated why. The new study indicates that congestion in axons is the likely culprit behind amyloid-filled plaques and tau-rich tangles. What's more, Goldstein says, the jams may explain tau's role in the disease process. Tau is key to regulating traffic on the axon highways, and even a slight blockage can lead to serious neuron damage.