Scientists are beginning to understand how the brain flushes out waste products in order to stay healthy and fend off neurological diseases.

Two teams of scientists from Washington have uncovered signs that a slow wave of electricity that pulses through the brain during sleep pushes waste products, including the protein closely associated with Alzheimer's disease, from deep in the brain to its surface.

A vein passing through the brain then acts as a pipe to carry waste products out through the barrier that separates the brain and the rest of the body. This deposits them into the bloodstream to be filtered out by the kidneys. 

But if the disposal system stops working correctly, which can occur with aging, in cases of traumatic brain injury, and chronic stress, those waste products can accumulate in the brain. 

It may also allow immune cells to penetrate the organ, leading to inflammation linked to degenerative brain disorders.

The study was conducted in mice, but researchers believe their findings match up with research on potential causes of Alzheimer's disease and other dementias.

In February, scientists led by Dr Jonathan Kipnis, a neurologist at Washington University in St Louis, answered the question of how the brain gets waste out through the rigid protective barrier without using the body's lymphatic system, a network that drains fluids throughout the body.

The brain is not part of that system and its waste disposal pathway is known as the glymphatic system. It clears out waste generated by energy-consuming metabolic processes - all the chemical processes continuously working in the body to ensure it functions correctly - such as carbon dioxide, damaged proteins and dead cells.

Scientists uncovered exit points around the brain from which cerebrospinal fluid, which carries waste, flowed out to the thick membrane surrounding the brain and spinal cord and into the bloodstream, where the body's lymphatic vessels took over to clear it out.