Emotions. Yeah. One of the false myths about intelligence is the Spock hypothesis: that we can somehow separate logic from emotion. It is my assertion that emotion is the fundamental component of consciousness: the feedback loop mechanism that reinforces memory and nerve connections in order to maintain a model of the world and our self. Without that mechanism, consciousness can't happen.

A disease that affects people's emotions, then, will affect decision making and intelligence, especially in children who are building a model of their world inside their brains. We can only see physical shrinking of the brain in scans, not the exponential effects on connections and intentions. The closest probable correlation is fatigue levels. Tired people don't read, move or interact with the world as much. The less they interact, the less they care. The less they care, the less they think.