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Arousal is a physiological and psychological state involving the activation of the reticular activating system in the brain stem, the autonomic nervous system and the endocrine system, leading to increased heart rate and blood pressure and a condition of alertness and readiness to respond.

There are many different neural systems involved in what is collectively known as the arousal system. Four major systems originating in the brainstem, with connections extending throughout the cortex, are based on the brain's neurotransmitters, acetylcholine, norepinephrine, dopamine, and serotonin. When these systems are in action, the receiving neural areas become sensitive and responsive to incoming signals.

Arousal is important in regulating consciousness, attention, and information processing. It is a crucial for motivating certain behaviours, such as the fight or flight response and sexual activity (see Masters and Johnson's human sexual response cycle, where it is known as the arousal phase). It is also very important in emotion, and has been included as a part of many influential theories such as the James-Lange theory of emotion. According to Hans Eysenck, differences in baseline arousal level lead people to be either extraverts or introverts.

The Yerkes-Dodson Law states that there is a relationship between arousal and task performance, essentially arguing that there is an optimal level of arousal for performance, and too little or too much arousal can adversely affect task performance. One interpretation of the Yerkes-Dodson Law is the Easterbrook Cue-Utilisation hypothesis. Easterbrook states that an increase of arousal leads to a decrease in number of cues that can be utilised. (Easterbrooke, 1959).

• Emotion
• Emotion and memory
• Sexual arousal
• Yerkes-Dodson law

• Easterbrooke, J.A. (1959). Psychological Review, 66, 183-201.