(iii) Hormonal influence There are many such motives, including hunger, thirst, a desire for sex, temperature regulation, sleep, pain, avoidance and a need for oxygen.
1. Hunger Motivation:
There are three theories that explain hunger motivation: (a) Stomach contractions theory. (b) Glucose or blood-sugar level theory. (c) Role of hypothalamus. (a) Stomach Contractions Theory: Earlier it was believed that hunger is due to contraction of stomach. However, various experiments have shown that there is no relationship between stomach contraction and hunger.
Research studies have shown that people report normal feelings of hunger even when for medical reasons, the nerves from the stomach have been cut or the stomach have been entirely removed. (b) Glucose or Blood Sugar Level Theory: Is another theory which explains the relationship between hunger and blood sugar level. According to this theory the cause of hunger is low levels of blood sugar. Research evidence for this theory is lacking. (c) Role of Hypothalamus: The hypothalamus has long been considered important in the regulation of the hunger motivation. The classic work of the 1940s and 1950s emphasized the contributions of two regions of the hypothalamus, namely the lateral hypothalamus (LH) and the Ventromedial hypothalamus (VMH). The lateral hypothalamus was considered to be an excitatory region for hunger motivations, while the Ventromedial hypothalamuss was said to be involved in the cessation of eating that is satiety. These ideas were based on animal experiments in which the two areas were either destroyed by lesions or electrically stimulated by means of small wires called as electrodes placed in the brain.
Electrical stimulation of the lateral hypothalamus was found to elicit eating. Ventromedial stimulation was found to stop ongoing eating behaviour. The lesions made in the two areas were found to have effects opposite to those of stimulation. Animals with damage to the lateral hypothalamus would not eat and drink and eventually died of starvation unless given special care. When the damage was done to ventromedial area the animal developed voracious appetites, consumed great quantities of food, and gained weight rapidly. It was found that the rats with ventromedial lesions may become two or three times heavier than normal.
After initial spurt of weight gain, the animal with VHM lesions reached a new baseline weight at which they maintained themselves. Humans with tumors of the brain or other conditions that have damaged the VHM area overeat and become obese. The results of these early studies were interpreted as indicating that the LH is a feeding centre while the VHM is a satiety centre.
2. Thirst Motivation:
Is another biological motive. Once it was believed that thirst was due to dryness of throat. However, this view is outdated today. Today it is believed that thirst is due to water level in the body.
Water level of the body can be influenced by certain hormones. One type of hormone which influence water level of the body and causes thirst is called as Antidiuretic hormone (ADH). Another theory which explains thirst motivation is called as Double Depletion Hypothesis. According to this hypothesis thirst is due to: (a) Cellular dehydration.
(b) Hypovolemia. According to cellular dehydration theory, there are certain nerve cells in front of hypothalamus. These nerve cells are called as Osmoreceptors which generate nerve impulses when they are dehydrated. These nerve impulses act as a signal for thirst and drinking. Thirst triggered by loss of water from the osmoreceptors is called cellular dehydration. Loss of water from the body also results in hypovolemia, or a decrease in the volume of the blood. This results in thirst.
3. Sexual Motivation:
Sexual motivation is another very important motive which is classified as a biological motive. But besides its biological base it also has social and psychological base. Sexual motivation is considered to be biological because hormones and neurons play an important role in eliciting sexual drive. Sexual motivation is social because it involves other people. Sexual behaviour is powerfully regulated by social pressure and religious belief. Sex is psychological in the sense that it is an important part of emotional lives, it can provide intense pleasure, but it can also cause us agony or involve us in many difficult decisions. Sexual behaviour, though a biological motive, differs from other biological motives as follows: (i) Sex is not necessary to maintain the life of an individual although it is necessary for the survival of the species.
(ii) Sexual behaviour is not aroused by lack of substance in body. (iii) In higher animals, at least, sexual behaviour is more under influence of sensory information from the environment. Human beings considerably influence not only our sexual behaviour but also influence the development of primary as well as secondary sex characteristic. In female the sex hormone secreted is Estrogen and Progestorene. One important type of estrogen is estradiol.
Progestorene plays an important role in pregnancy. The male sex hormone is Androgen; one important type of androgen is testosterone. Sex hormones in lower animals trigger sexual behaviour. For e.g. high levels of estrogen in blood of females of lower species trigger sexual behaviour. However the relationship between human sexual behaviour and sex hormonal level has not been proved. Males need a certain level of testosterone in order to maintain their sexual interest and to engage in sexual behaviour.
Castration of lower animals and to a lesser degree of human males reduces their sexual drive. External stimuli and learning play an important role in sexual motivation and expressions of sexual behaviour. Cultural factors also influence sexual behaviour. Fantasy, imagination and thought also considerably influence sexual behaviour in human being.