Physiological Motives I - Hunger

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Motivation can be categorized according to its sources as well as the factors theorized to influence it. Most motives researched can be thus categorized as physiological, learned, due to a combination of biology and learning, or related to human effectance.

Physiological motives are driven by biological needs and internal bodily states. The most thoroughly researched physiological motives are hunger and thirst. 

Early research on hunger focused on localizing(identifying physical origins for ) the sensations and energy that drive eating behaviour. Classic research by Walter B. Cannon(1871-1945) initially concluded, erroneously, that the stomach contractions that accompany hunger pangs are themselves the physical stimulus for eating behaviour.

Later research rejected this simplistic localization in favour of a more physiological explanation. Hunger is generally cyclical, corresponding to the rhythms of homeostasis, the bodily balance essential to healthy function. When nutrients are needed to fuel the body, the individual feels hungry; when one is well-nourished, one feels sated and disinclined to eat further. 

Brain research has identified the 'location' of the body's hunger signals as cells within the hypothalamus, a part of the limbic system that is integrally involved in motivation and emotion.




Cells in the lateral hypothalamus(LH) ( the sides of the structure) appear to function as a 'start' centre, sending signals to 'eat' when the concentration of glucose, a simple sugar, in the bloodstream is low. Conversely, cells in the ventromedical hypothalamus(VMH) (a front, central region of the structure) function as a 'stop' centre, indicating satiety, a level of adequate glucose concentration. 

Together, the LH and VMH comprise a lipostat, a brain centre that measures the nutrient level of the bloodstream and regulates eating behaviour to maintain that ideal balance, or setpoint. 

Some research suggests that individuals with eating disorders may be suffering the effects of an altered setpoint, feeling hungry when they are physically sated(obesity), or feeling sated when they are physically starving (anorexia).



Research comparing obese with normal weight individuals indicates that eating behaviour is influenced by external factors as well as by hunger(an internal state).

Obese individuals(whose body weight is 20% above ideal body weight for their height and build) are more influenced than normal-weight individuals by the smell, taste, and texture of food. Their eating behaviour is also more influenced by time (eg. whether it appears to be mealtime) and sensory access to food (eg. seeing a bag of snack food close at hand) than is that of normal-weight individuals. 

Across weight levels, people's eating behaviour is strongly influenced by social factors, including cultural preferences and aversions to certain foods, norms for which foods are served for specific mealtimes, and the role of food in accompanyin gdocial activities. For humans, eating is a complex behaviour, strongly but not exclusively influenced by internal signals of hunger.



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