Arousal is a continuum of sensitivity of the organism to stimuli, both external and internal. Arousal:
- Facilitates interaction with the environment in a context-specific manner (e.g., under conditions of threat, some stimuli must be ignored while sensitivity to and responses to others is enhanced, as exemplified in the startle reflex),
- Can be evoked by either external/environmental stimuli or internal stimuli (e.g., emotions and cognition),
- Can be modulated by the physical characteristics and motivational significance of stimuli,
- Varies along a continuum that can be quantified in any behavioral state, including wakefulness and low-arousal states including sleep, anesthesia, and coma,
- Is distinct from motivation and valence but can covary with intensity of motivation and valence,
- May be associated with increased or decreased locomotor activity, and
- Can be regulated by homeostatic drives (e.g., hunger, sleep, thirst, sex).