A few things to know about this particular study:

• It was done in women… this doesn’t necessarily mean the effect doesn’t exist in some form in men (they just don’t know).
• Personality assessment was done using something called the Eysenck Personality Inventory, which is a commonly administered test to rate a person’s disposition, emotional stability and relative tendency toward introversion, associated with shyness or reserve, or extraversion, used to describe more outgoing people.
• Stress was defined as anything stirring feelings of anxiety, irritability, tension, fear, nervousness or sleep disturbances.
• Being extroverted or introverted on its own did not appear to heighten the risk of dementia, although the study found that women who were easily distressed and also tended to be introverted were at the highest risk for Alzheimer’s.