In the 1880s, William James provided the first modern version of such theories. Somatic theories of emotion claim that bodily responses are essential to emotions, rather than judgements. The following are a few theories and areas of study of the mind used to further our knowledge of the mind. However, much has been discovered in the study of the brain.

The psychological study of mood is built on theories. When attempting to discover the biological factors that influence mood, it is difficult to find scientific proofs. Mood is the state or quality of feeling at a particular time. However, it seems that only authentic moods have the power to produce these mood-dependent effects. Thus, the likelihood of remembering an event is higher when encoding and recall moods match up. Unlike mood-congruent memory, mood-dependent memory occurs when one's current mood resembles their mood at the time of memory storage, which helps to recall the memory. The associative nature of memory also means that one tends to store happy memories in a linked set. An individual's present mood thus affects the memories that are most easily available to them, such that when they are in a good mood they recall good memories (and vice versa). When one encodes a memory, they not only record sensory data (such as visual or auditory data), they also store their mood and emotional states. Mood dependence is the facilitation of memory when mood at retrieval is identical to the mood at encoding.

State dependent memory