The immune system as a sensory system: Implications for psychology

The brain and immune system form a bidirectional communication network in w hich the immune system operates as a sense organ to provide the brain with information about infection and injury; thereby allowing the brain to coord inate a defense. Activated immune cells release proteins called cytokines, which signal; the brain by both blood and neural routes. Information that r eaches the brain across this sensory channel produces large changes in neur al activity, behavior, mood, and cognitive functioning. Appreciation of the functioning of this network may illuminate poorly understood aspects of st ress, depression, and intraindividual variability in behavior, mood, and co gnition.