Although many of the above psychological characteristics cannot be measured in animals, some behavioural traits associated with resilience have been identified. In numerous animal models (see Supplementary information S1 (box)), rodents display a range of responses to stress: at one extreme are active or `fight-flight' responses (for example, attempts to escape and aggression), and at the other extreme are passive responses (for example, freezing and submission)27. Active-coping animals are often considered to be resilient, based on numerous functional end points, whereas their more passive counterparts are not; however, both types of responses can be seen as adaptive depending on the particular context. The availability of these animal models has made it possible to study the neurobiological and molecular mechanisms that underlie these behavioural traits, as is discussed below.
