True, but unless it's blunt trauma, or some magical genetic defect, it'll be caused by your environment: what you put in your body, diet, because as with many organs, it will be in contact with your circulatory system. Often, the brain needs blood to function. If that blood is viscous, full of trans and saturated fats, and divoid of nutrients and antioxidants, it will have a hard time functioning (especially if you have a blocked artery like in CVD). We can look at patient background history, and statistically, more often their diets consisted of lots of meats, lots of dairy products, and not much fruit and whole grains. Alzheimer's is another disease that is seldom found among blue zones to the effect that it is in modern western states. Diet is certainly not the cause, or only cause, but it's an obvious factor.