Or quite well correlated like flying kite with metal strings during a storm and getting hit by lighting.
After all we know that people are social animals, that we acquire language and reasoning abilities by interacting with others in childhood (and children that are prevented from doing that have developmental problems), and that forced isolation in adults (in prison, lost in some forrest, or whatever) also brings several psychological and mental problems, and can even be used as punishment and torture.
If "decreased cognitive function" was the cause, then it should have been there before (or at the very beginning) of the social isolation (to cause it).