fear is controlled, in part, by an area of the brain called the limbic system. The limbic system 
includes some of the deepest, most primitive structures of the brain—structures shared 
by many less “evolved” animals. In fact, there is reason to believe that the emotion of fear 
is present across most, if not all, animal species. Most organisms display speciﬁc patterns 
of behavior when confronted with danger and often these “fearful” behaviors include 
forms of aggression or escape. Therefore, the intense feelings we experience when we are 
exposed to an immediate danger often are called the “ﬁght-or-ﬂight” response.
Although most people use the terms “anxiety” and “fear” interchangeably, behav -
ioral scientists who study emotions assign somewhat different meanings to these and 
other related terms (Barlow 2002; Suárez et al., in press). Anxiety is a future-oriented 
feeling of dread or apprehension associated with the sense that events are both uncon -
trollable and unpredictable. In other words, anxiety is a nagging feeling that occurs when 
a person believes a negative event may occur in the future and that nothing can be done 
to prevent it.
People who feel anxious tend to dwell upon and ruminate about the possibility of 
danger. This tendency to dwell on future negative events is called worry. Anxiety is also 
associated with uncomfortable physical feelings such as arousal (for example, sweatiness, 
increased pulse), tension (for instance, tight muscles), and pain (like headaches).