Our brains are protected by a shield known as the blood-brain barrier (BBB). It gets its name because, in a healthy brain, components of the blood are excluded from the brain tissue by a barrier made up of different cells and other factors, which creates a division between the circulatory system and the brain. We call this barrier semi-permeable, meaning that only certain molecules important for the brain's functioning are allowed to cross. As we get older, this barrier becomes "leaky," allowing forbidden molecules to enter.
When we are young, the BBB is intact. During middle age, we find the first evidence of wear-and-tear. A small percentage of people begin to have blood proteins in a part of the brain called the hippocampus. Hippocampus means seahorse in Greek, representing this brain area's curved shape. The hippocampus is one of the most important and adaptable brain regions. When you experience something new, your hippocampus responds by forming novel connections between brain cells called neurons, and sometimes removing old connections as well. This making and removing of connections is called plasticity and through this plasticity, the hippocampus plays an important role in learning and memory.

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