Does low blood pressure affect the brain?

Certainly can: It really depends on the person, and how low "low' is! some people can have a very low blood pressure, even with the first number (systolic) being less than 100, and be absolutely fine. Most people will complain of being dizzy with a lower than their normal bp, especially if it drops when they stand (orthostatsis) as less blood gets to the brain.Hypotension can cause confusion too.

Sometimes...: Low blood pressure, if low enough, can decrease blood flow to the brain. Since blood carries oxygen, the person would then have low oxygen to the brain. The brain doesn't function well with low blood flow/oxygen and the person could experience light-headedness, confusion, etc. And may even pass out.