Early theories of motivation focused on instinct and drive reduction and dealt primarily with biologically based behavior. More recent theories ascribe complex human behavior to expectations, values, and needs for achievement and self-esteem.
The basic biological motivations are thirst and hunger. The three major stimuli including thirst are increased salt concentration in body fluids, decreased amount of fluid in the circulatory system, and energy expenditure or decreased body temperature, both of which result in sweating. The mechanism that regulate eating are, internally, stomach contractions and distention and, outside awareness, monitoring of glucose and insulin levels in the body by the hypothalamus. External stimuli also affect eating, the sight and aroma of food act as cues to which some people are more vulnerable than others.
Motivation to obtain some standard of excellence has been one of the most studied aspects of social motivation. In contrast to pole with low achievement motivation, those with high achievement motivation attempt harder tasks, persist longer, and choose goals that are challenging but not overwhelmingly difficult.
Achievement striving can be analyzed as extrinsically (for some reward) or intrinsically (for enjoyment and satisfaction) motivated. Extrinsic motivation can sometimes undermine intrinsic motivation, producing over justification effect.
The need for self esteem may be a very powerful, encompassing need, governing both achievement and intrinsic motivation. People generally strive to maintain an overall positive self-image by overestimating their control over the future and avoiding situations that reveal shortcomings.
We regulate our own behavior periodically assessing it in relation to our goals and values. A great discrepancy produces emotional discomfort, which motivates us to reduce that discrepancy and bring our behavior into line.