While it has not gotten as much attention as vitamin B12, multiple studies have investigated the relationship between vitamin B6 and dementia and its potential role as a treatment. A study published in 2002 looked at the relationship between B6 levels, homocysteine levels, and the incidence of cerebrovascular disease in people with Alzheimer's. They found that unusually low levels of vitamin B6 were prevalent in people with Alzheimer's, and also reported a correlation between elevated levels of homocysteine and the development of cerebrovascular disease. They conclude their report by calling for future studies investigating vitamin B6 as a potential treatment for Alzheimer's.
In 2006, another study looked at the relationship between dietary intake of B6 and other B vitamins and the risk of developing Parkinson's later in life. The researchers found that "Higher dietary intake of vitamin B6 was associated with a significantly decreased risk of PD [Parkinson's]." While B6's effects on homocysteine could definitely be beneficial, they hypothesized that it was actually its antioxidant properties that accounted for most of its protective effect.