The Circle of Willis is a ring or circle of arteries located at the base of the brain. It is also known by several other names, most commonly the cerebral arterial circle and arterial Circle of Willis. This part of the brain was first discovered by the English doctor Thomas Willis in the 17th century. The circle is important to itself and the brain, because the way the arteries are laid out provides a form of backup in case any of them is obstructed. If one artery is constricted or blocked, the flow of blood from the other arteries in the circle will most often be enough to preserve the necessary flow to the brain and prevent damage.
Once the Circle of Willis was discovered, years of research were conducted into its purpose and functions. It has been determined that the circle provides the necessary blood and fuel for all thought processes and even physical processes in the brain. This very efficient cluster of arteries essentially provides all of the blood that comes and goes from the brain, which it needs to survive and operate.
While it has been discovered that the looping pattern in which the arteries lay creates reinforcement for blood flow and greatly reduces the risk of blood pressure changes in the brain, it is not completely infallible. Some blockages caused by debris or blood clots or even hemorrhages are still able to cause devastating effects such as strokes. Sometimes even death can occur if these blockages happen to be large enough or occur in just the wrong spot.
Many assume that this structure can be represented correctly by the diagrams shown in books, which is much more complex in shape than a simple circle. The truth, however, is that about two-thirds of the human population does not have a complete “circle" — most have one or more connections missing. No concrete evidence supports that a person with an incomplete Circle of Willis is at greater risk for strokes.
While the Circle of Willis may not be studied as closely as higher functions of the brain and thought, it is generally accepted as the most important part of the brain. Without this structure, blood would not flow properly to the brain and its functions would be impossible. It is often said that life itself would not even be possible without this vital structure to keep blood flowing regularly.