The health value of a Mediterranean diet is widely known. Fruits, vegetables and fish are main foods in this diet.

Extra-virgin olive oil is also a major part of the Mediterranean diet. And new research shows that it may protect the brain from losing its ability to work properly.

Researchers at Temple University in Philadelphia, Pennsylvania say extra-virgin olive oil "protects memory and learning ability." Extra-virgin olive oil, also called EVOO, can reduce the formation of poisons in the brain that are signs of Alzheimer's disease.

But how does it do it? Researchers say olive oil reduces inflammation in the brain. It also activates a cleaning process. This process is called autophagy.

Autophagy is when cells break down waste and poisons found between cells and remove them from the body.

There are two substances in the brain most closely linked to memory loss in Alzheimer's patients: amyloid plaques and neurofibrillary, or tau tangles.

For definitions of both amyloid plaque and tau tangle, we go to experts at New Jersey’s Rutgers University and the U.S.-based Alzheimer's Organization.

Amyloid is a protein normally found throughout the body.

However, the experts say when amyloid grows abnormally it creates a sticky build-up called plaque outside the nerve cells, or neurons. This abnormal amyloid plaque slowly kills the cells.

Tau proteins are common in the central nervous system. Tangles form inside dying neurons. Tangles are twisted fibers of tau protein.

Experts from both organizations explain that, normally, every neuron contains long fibers made of protein. These proteins hold the neuron in its proper shape. They also help to transport nutrients within the neuron.

However, in brains with Alzheimer's disease, these fibers begin to tangle. This causes the neuron to lose its shape. The neuron also becomes unable to transport nutrients. Over time, it dies.

Domenico Pratico is the lead researcher of the Temple University study.

He says, "brain cells from mice fed diets enriched with extra-virgin olive oil had higher levels of autophagy" and lower levels of the poisons -- the amyloid plaques and tau tangles.

For their study, the researchers looked at mice that had three traits of Alzheimer's: memory loss, amyloid plaques, and tau tangles.

They put the mice into two groups. Researchers gave one group a diet with extra-virgin olive oil. They gave the other group a diet without EVOO.

The olive oil was given to the mice when they were only six months old. This was before any symptoms of Alzheimer's had set in. At age 9 months and 12 months, the mice in the olive oil group performed considerably better on tasks that tested the mice's memory and learning ability.

And, the scientists reported differences in the brain tissues of the two groups.

The brains of the olive oil group showed a great increase in nerve-cell autophagy. This cell-cleaning process is responsible for the lower levels of the poisons we talked about earlier -- the amyloid plaques and tau tangles.

Pratico says that "one thing that stood out immediately was" the strength of the synapses.

A synapse is the connection between neurons. It is how they communicate. The synapses in the mice on the EVOO diet were stronger than those in the other group.

The researchers say their next step is to see what happens to mice who are given olive oil at 12 months. At that time, they will have already begun to show signs of dementia.

Pratico says that patients usually have dementia when they visit a doctor to investigate signs of the disease. He says the researchers "want to know whether olive oil added at a later time in the diet can stop or reverse the disease."

The researchers published their findings online in the Annals of Clinical and Translational Neurology.