Motivation and emotion/Book/2017/Hormones and motivation

Overview
'Have you ever felt hungry but not enough to get something to eat? After an hour, your hunger grows until your number one priority is to get food. These are the sort of innate drives and motivations that humans encounter on a daily basis.'

Hormones can play a key role in determining if you really feel motivated to follow through with something or not. Two major areas of innate motivation are hunger and sex. Both of these areas are essential for humans to not only stay healthy, but to reproduce. This book chapter will attempt to determine what the key hormones influence these behaviours are and what effect they play on an individual’s level of motivation.

Key questions
 * What are the key theories relating to hormonal motivation?
 * What are the key hormones related to basic human motivation?
 * How do these hormones influence motivation?

Theories of motivation


In early understandings of motivation, it was thought that the pleasure which was experienced when a basic need was met, such as eating, was the ultimate determinant of human motivation (Gardener, 2000). This type of motivation was known as drives and dominated the early motivation theories, however it later lost favour due to its inability to explain human behaviour that produced tension, rather than reduce it. As an example, drives could not explain why people skydive when it induces fear and anxiety (Gardener, 2000).

Despite losing favour with more current theories of motivation, drives still play a critical part in the overall understanding of a basic level of motivation. As animals, humans have a set of requirements that need to be met or psychological and physical damage may be done. Drives are the key to ensuring that these requirements take precedence when it is required.

Sigmund Freud was the first to hypothesise that motivation was driven by the bodies biological needs. He believed that urges such as finding warmth or hunger were predictably recurring which produced energy build-ups in the central nervous system. If these energy build-ups were to get to large, Freud believed that it could threaten the individuals physical and psychological health (Reeve, 2015). With further understanding of the human body, Freud can be seen to be correct in that the build-up of hormones can force us to prioritise something such as eating over watching the TV.



In 1945, Abraham Maslow determined that there were five physiological and psychological needs that humans required; physiological, safety, belonging and love, esteem and finally self-actualisation. These five steps are ranked from most basic – being physiological needs – to most complex – self actualisation (Maslow, 1943).

In 1969, Maslow introduced a sixth need above self-actualisation. This need was self-transcendence and worked on the theory that humans need something to constantly aspire to and to further a cause beyond the self. Physiological needs are the basic needs in life which include, finding shelter, food, water, sleep and reproduction. As these needs are the most important to life they should be met first, hence they are on the bottom of Maslow's pyramid.

One of the key concepts of physiological needs constructed by Maslow, was that of homeostasis and the efforts by the body to create a state of equilibrium. The human body uses many different methods to maintain homeostasis with one of the main contributors being hormones. These hormones can include ghrelin and leptin in regards to hunger or testosterone and other sexual hormones.

Sex hormones as motivators


Sexual motivation research in mammals has primarily focused on pre-sexual behaviours (Alexander, Packard & Hines, 1994). More recently, however, research has moved to look at a more appetitive approach to sexual motivation. This means it now focuses on the expectation of the rewarding consequences of sexual contact which includes the responses prompted by the association of the goal (Alexander, Packard & Hines, 1994). These appetitive responses are defined as being anything which reflects the central motivational state for attainment of a goal and can be adapted by learning (Bindra, 1974).

One key determinant must be made when discussing sexual motivation – the differences between the ability to engage in sexual activities and the desire to do so (Wallen, 1990). Typically, when discussing sexual motivation, sexual desire is the key concept being referred to as it is this desire or drive that provokes the individual to engage in such activities rather than their capacity.

Social context is also another factor to be considered when discussing sexual motivation in humans. In other animals, such as monkeys, social hierarchy is the main element of social construct in sexual behaviour. In humans, however, we have created many other elements to social constructs that have large effects on sexual motivation and behaviour. For example, human cultures restrict the ages of mates, places and times where sexual behaviour is appropriate or not (Wallen, 2001).

It is clear that hormones play a major role in sexual motivation. This can be seen through studies where surgically menopausal women report a decline in sexual desire which was reversed through hormonal therapy (Dennerstein, Wood, and Burrows, 1977).

Testosterone


Testosterone is a steroid hormone which is derived from cholesterol. In males it is produced in the testes, and in females in the ovaries and adrenal cortex (Mehta & Joseph, 2011). Testosterone is responsible for many physical and physiological developments in humans. These include the development and maintenance of masculine characteristics, supporting basic physical development and is also heavily involved in regulating social behaviour (Mehta & Joseph, 2011).

Many studies have demonstrated an association between individuals with higher levels of testosterone and a more dominant social status. The dominant trait includes being more aggressive, and more socially dominant than individuals with lower levels of base testosterone (Archer, 2006; Archer, Birring & Wu, 1998).

Increased testosterone levels in blood plasma have shown to have rewarding properties which indicates that testosterone regulates neural systems involved in the reward process. Sexual stimuli induces a rapid testosterone secretion which as previously noted gives the individual a positive and rewarding experience (Alexander, Packard & Hines, 1994). Age related decline of testosterone levels have shown to lead to decreased libido, as well as a multitude of other negative affects (Sternbach, 1998).

Higher testosterone levels, at a basic human and animal level, leads to a higher level of sexual motivation. At a basic level, social context is important in reproduction and there is clear evidence to show that higher levels of testosterone lead to an individual having a more dominant social status. The rewarding properties of testosterone coupled with its rapid secretion when exposed to sexual stimuli further demonstrate that testosterone is a positive motivator of sexual activity.

Oestrogen and progesterone
In females, oestrogen and progesterone are often the main regulators of sexual motivation. Oestrogen plays a key role in promoting sexual motivation through many different means including the sense of smell (Wallen, 2001). There has been debate whether it is in fact oestrogens or androgens that regulate the sexual behaviour of females, however studies investigating the changes in daily hormones and the changes in behaviours have provided some clarity. Oestrogen has shown to correlate significantly with increased sexual motivation, whereas progesterone significantly correlated with decreased motivation. These studies also showed that there was no significant correlation between testosterone and any pattern of sexual behaviour in females (Wallen et al, 1984). These studies demonstrate that ovarian functions, specifically the release of oestrogen and progesterone in females play a significant role in regulating sexual motivation in females.



Oxytocin
Oxytocin is secreted from the posterior pituitary gland typically during sexual stimulation (for example touching of the breasts or genitals). In a study on rats, oxytocin levels were shown to be highest in sexually inexperienced males who are coupled with a sexually proceptive female (Hillegaart, Alster, Uvnäs-Moberg & Ahlenius, 1998). Sexually experienced males showed lower levels of oxytocin in general than the inexperienced males. This indicates that males who face a situation-specific demand for action, in this case mating with the female, have a higher release of oxytocin. It can be determined from this study that oxytocin can help promote sexual motivation, particularly in sexually inexperienced males.

Hunger hormones as motivators
Consuming food is critical to the survival of all in the animal kingdom. Mammals in particular have a difficult task achieving adequate food in order to regulate body temperature and maintain a metabolic rate. As such, a complex hormonal system is required to ensure that food is being eaten at the correct times and not eaten at the wrong times (Saper, Chou & Elmquist 2002). When blood glucose levels deplete, ghrelin is released to invoke a feeling of hunger. If food is not eaten, the feeling will gradually get larger and larger until the craving has been satisfied. It is this drive that makes hunger a powerful form of motivation.

Ghrelin


Ghrelin is a hormone produced in the oxyntic glands and secreted by epsilon cells which are found in the bottom of the stomach (Kageyama, Takenoya, Shiba & Shioda, 2010). So far, ghrelin is the only gastrointestinal hormone which demonstrates stimulating appetite (Hellstron, 2009). Discovered in 1999 by Kojima and colleagues, Ghrelin showed to increase during a fasting state or before a meal in order to promote the consumption of food in humans.

Levels of the hormone were also shown to decrease after the consumption of foodstuffs which gives a key indicator that ghrelin is a highly important signal to induce appetite and hunger (Kojima et al., 1999). Ghrelin has receptors which are located in the hypothalamus in order to regulate food intake and satisfaction (Muller et al., 2015).

Research has found that both intraperitoneal or intravenous infusion of ghrelin promotes a feeding behaviour which is similar to that of a intracerebroventricular administration. This indicates that ghrelin moves its appetite inducing signal from the periphery to the central nervous system which in turn will notify the hypothalamus to prompt the action of eating (Asakawa et al., 2001).

Ghrelin causes the human body to increase appetite and in turn drive a desire to eat. As the energy and food sources deplete, ghrelin is released to try and retain homeostasis in the body (Cowley et al., 2003). This drive is what was previously theorised as being a key form of motivation in humans. It can be determined from the effect of ghrelin on the human body that it has a large role to play in this particular form of motivation.

 "Steve finishes a big, delicious dinner at 6pm and goes to bed at 10pm. He wakes up again at 7am."
 * Ghrelin levels peaking just before eating
 * Leptin levels peak after eating
 * Ghrelin levels decrease after eating dinner
 * While sleeping and fasting, Steve's ghrelin levels have increased which will make him hungry in the morning

Leptin


Since its discovery in 1994, Leptin has played a large role in clarifying the communication between the brain and energy stores (Ahima & Antwi, 2008). Leptin is expressed by adipocytes and the levels of leptin in in adipose tissue and blood directly correlates to the mass of the adipose tissue and triglyceride content (Ahima & Antwi, 2008). This means that leptin levels are increased during weight gain and decrease during weight loss (Myers, Cowley & Münzberg, 2008).

Leptin's main function is to, much like ghrelin, communicate energy stores to the central nervous system which in turn notifies to body to suppress food intake and allow energy expenditure (Bates & Myers, 2003). Leptin works on a homeostatic basis in that when the body’s energy stores are filled, leptin is released to return the stores back to a normal state of equilibrium. When the gut-brain axis communicates to the brain that eating is taking place, ghrelin levels begin to fall and leptin levels begin to rise which ultimately leads to the cessation of eating and the use of energy (Berthoud et al., 2017).

Leptin plays an important role in supressing the motivation to eat more food when it isn’t necessary. Together with ghrelin, leptin maintains a level of equilibrium and ensures that the drive to eat and the drive to release energy is controlled.

Quiz
Choose the correct answer and click "Submit": {When are ghrelin levels highest in the body? + Before eating - During a meal - After eating - Both before and after a meal
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Conclusion
The motivational drive to eat which commences when the body is low on food stores is generated by hormones. Ghrelin ensures that when we need to eat in order to survive, we find food and eat. Leptin on the other hand lets us know when we have eaten enough to ensure we stay healthy and don’t become unwell or overweight.

Testosterone plays a significant role in ensuring that males in particular are sexually motivated. Its strong positive effects paired with its rapid secretion when exposed to sexual stimuli solidify it as a key contributor to sexual motivation. Studies have shown that increased oestrogen correlated with increased sexual motivation in females. Oxytocin again shows strong links to increased sexual motivation, particularly in inexperienced males.

As more recent literature surrounding motivation has noted, drives are not the only factor influencing motivation. This in turn means hormones aren't the only influence of different motivational states, however it is clear that they do contribute large role and effect on innate motivational behaviours and drives. There are many hormones which are still not fully understood, so it is very likely that there are more aspects to this topic that can be discussed in the future. Ultimately, it is important to understand that in order for human psychology to function correctly, the appropriate hormones need to be acting in the appropriate ways. If these hormones fail to function correctly it can lead to psychological and physical health issues.