Arousal

Arousal is a physiological and psychological state of being awake or reactive to stimuli. It involves 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 sensory alertness, mobility 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.

Importance
Arousal is important in regulating consciousness, attention, and information processing. It is crucial for motivating certain behaviours, such as mobility, the pursuit of nutrition, 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. Later research suggest it is most likely that extroverts and introverts have different arousability. Their baseline arousal level is the same, but the response to stimulation is different.

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.

In positive psychology, arousal is described as a response to a difficult challenge for which the subject has moderate skills.

Abnormally increased behavioral arousal
This is a state caused by withdrawal from alcohol or barbiturates, acute encephalitis, head trauma resulting in coma, partial seizures in epilepsy, metabolic disorders of electrolyte imbalance, Intra-cranial space- occupying lesions, Alzheimer's disease, rabies, hemispheric lesions in stroke and multiple sclerosis.

Anatomically this is a disorder of the limbic system, hypothalamus, temporal lobes, amygdala and frontal lobes. It is not to be confused with mania.