Parker's lethargic attitude and unwillingness to participate in school are most indicative of "depression." His personality has not been affected, but more so his mood and his outlook. His lack of energy is not a sign of mania and his intact personality rules out disassociate identity disorder and post traumatic stress disorder. 

Mood-congruent memory is the tendency to recall experiences that are consistent with one's good or bad mood. Thus, if the subject is upset, he is more likely to recall negative memories during which he experienced a similar emotional state.

There are seven "basic" emotions that have been observed in nearly every culture on earth, and are recognizable between cultures even if those cultures have never interacted previously. These fundamental emotions are: joy, sadness, anger, fear, surpise, contempt, and disgust. Confusion is not one of the universal expressions.

The limbic system deals with emotion and memory. The corpus callosum connects the left and right hemispheres of the brain.

Positive psychology is a growing field of psychological research that seeks to grow the empirical data on optimal human functioning and positive emotions (e.g., longitudinal happiness)

Paul Ekman was primarily responsible for identifying many of the possible emotions of the human species and how these emotions were expressed facially. He argued that emotions were universal, though culture produced varying factors on to what extent they could be expressed and what situations/ideas would evoke which emotions. He came to this conclusion by studying emotions across cultures.

Richard Lazarus's theory of appraisal, which departs from a physiological explanation for emotion, posits that emotions are a result of people's subjective experience of an event. This theory is exemplified by the old tale of many different people looking at an elephant: each of these people will focus on different aspects of this elephant, like its ears, trunk, feet, etc. Likewise, someone's emotional experience of a busy road depends on his or her interpretation. Many might fear the busy road. Others accept it and feel content. Others focus on the sun outside and feel joy.

Emotions play a major role in signaling whether or not needs are being met. For instance, if we feel sad, this could be a signal that emotional, or even physical, needs are not being met. If we feel happy, this is a sign we've done something right that has fulfilled one need or another. There are other emotions, however, that are more complex. Things like surprise can be purely reactionary and unrelated to our needs, where our body is preparing itself to ascertain more information about the event (I.E. widening of the eyes to see more, opening the mouth for more respiration).

The statement used in the example is an example of a statement that, while discussing a psychological topic, is too general in nature to accurately reflect a valid psychological principle. Also, the statement offers no proof of its assertion, and does not mention any research in support of its assertion. Even if a statement seems intuitively accurate, in order for it to be a valid statement it must be specific, and supported by evidence.

The facial-feedback hypothesis is the idea that using the muscles involved in a certain emotion will make you feel that emotion. By expressing emotions with one's face, that emotion is intensified by the feedback loop created by this process.