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. It also is influenced by hormones and neurotransmitters such as dopamine, noradrenaline, serotonin, oxytocin, cortisol and GABA.