Population is based on the de facto definition of population, which counts all residents regardless of legal status or citizenship--except for refugees not permanently settled in the country of asylum, who are generally considered part of the population of their country of origin.
The brain is made up of over 100 billion nerve cells with each brain cell connected to around 10,000 other cells, which equals around 1000 trillion connections in your brain. Your brain is actually very soft, jelly-like, and not grey but a deep red in color. The brain controls both involuntary, or lower, actions, such as heart rate, respiration, and digestion. Complex, or higher, mental activity, such as thought, reason, and abstraction, is consciously controlled.
White matter disease is the wearing away of tissue in the largest and deepest part of your brain due to aging. This tissue contains millions of nerve fibers, or axons, that connect other parts of the brain and spinal cord and signal your nerves to talk to one another. A fatty material called myelin protects the fibers and gives white matter its color.