Arousal

Arousal refers to the physiological and psychological state of being awake, alert, and responsive to stimuli. It encompasses a broad spectrum of processes from basic sensory responsiveness to emotional and sexual activation. Arousal is not synonymous with attention or motivation, but it modulates the readiness to perceive, process information, and act.

Physiologically, arousal involves activation of brain arousal systems, including the reticular activating system, thalamus, and cortical networks, as well as autonomic and endocrine responses. The sympathetic branch of the autonomic nervous system increases heart rate, blood pressure, sweating, and pupil dilation. Neurochemically, norepinephrine from the locus coeruleus, along with dopamine, acetylcholine, and other neuromodulators, helps regulate arousal levels. Hormones such as adrenaline and cortisol can raise arousal in response to stress or challenge. Circadian and homeostatic processes also influence baseline and peak arousal.

Types of arousal include general or non-specific arousal, sexual arousal, emotional arousal, and sensory arousal. Sexual arousal is a coordinated set of physiological and psychological changes, such as vascular engorgement and increased genital responsiveness, driven by complex endocrine and neural circuits. Emotional arousal refers to the heightened response to emotionally salient stimuli, which can be positive or negative.

Psychological theories describe how arousal relates to performance. The Yerkes-Dodson law posits an inverted U-shaped relationship between arousal and task performance, with moderate arousal optimizing performance and very high or very low arousal impairing it. Arousal also interacts with attention, motivation, and cognitive load.

Clinically, dysregulated arousal can manifest as hypoarousal (reduced responsiveness) or hyperarousal (exaggerated physiological activation). Hyperarousal is common in anxiety disorders and post-traumatic stress disorder, while hypoarousal can occur in depression or certain sleep disorders. Arousal is typically measured via physiological signals such as heart rate, skin conductance, pupil dilation, or neuroimaging, and via subjective scales.