In psychology and philosophy, emotion is a subjective, conscious experience characterized primarily by psychophysiological expressions, biological reactions, and mental states. A similar multicompenential description of emotion is found in sociology. For example, Peggy Thoits described emotions as involving physiological components, cultural or emotional labels (e.g., anger, surprise etc.), expressive body actions, and the appraisal of situations and contexts. Emotion is often associated and considered reciprocally influential with mood, temperament, personality, disposition, and motivation. It also is influenced by hormones and neurotransmitters such as dopamine, noradrenaline, serotonin, oxytocin, cortisol and GABA. Emotion is often the driving force behind motivation, positive or negative. An alternative definition of emotion is a "positive or negative experience that is associated with a particular pattern of physiological activity."The physiology of emotion is closely linked to arousal of the nervous system with various states and strengths of arousal relating, apparently, to particular emotions. Emotions are a complex state of feeling that results in physical and psychological changes that influence our behaviour. Those acting primarily on emotion may seem as if they are not thinking, but cognition is an important aspect of emotion, particularly the interpretation of events. For example, the experience of fear usually occurs in response to a threat. The cognition of danger and subsequent arousal of the nervous system (e.g. rapid heartbeat and breathing, sweating, muscle tension) is an integral component to the subsequent interpretation and labeling of that arousal as an emotional state. Emotion is also linked to behavioral tendency. Extroverted people are more likely to be social and express their emotions, while introverted people are more likely to be more socially withdrawn and conceal their emotions.Research on emotion has increased significantly over the past two decades with many fields contributing including psychology, neuroscience, endocrinology, medicine, history, sociology, and even computer science. The numerous theories that attempt to explain the origin, neurobiology, experience, and function of emotions have only fostered more intense research on this topic. Current areas of research in the concept of emotion include the development of materials that stimulate and elicit emotion. In addition PET scans and fMRI scans help study the affective processes in the brain.