Emotions and emotional feelings arise through the integrated processing of bodily sensations, environmental events, thoughts and recollections, and they shape new learning, facilitate decision-making, and guide behavior. Mood and affect have been defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM) according to the durations of the emotions and emotional feelings comprising them. The development of functionally impairing pervasive and sustained disturbances of emotion and emotional feelings suggests a mood disorder such as major depression, dysthymia, mania, hypomania, or cyclothymia. Functionally impairing moment-to-moment disturbances of emotional expression and experience are disorders of affect. This category of clinical conditions includes disorders of affective excess such as pathological laughing and crying, pathological euphoria, essential crying, witzelsucht, and affective lability. The phenomenologies of emotional generation, expression, experience, and control reflect their putative neurobiologies. MacLean applied the principles of evolutionary neurobiology to the description of the limbic system and its function.