Role of Neural Mechanisms
Homeostasis:
Homeostasis involves mechanisms which bother detect the state of the internal environment and also correct the situation to restore it to its optimal state
There is, however, a significant time lag between mechanisms operating to restore equilibrium and the body registering their effect
By the time someone has eaten enough to restore energy levels, only a small amount of food has been digested, therefore the receptors responsible for detecting nutrient levels have insufficient 'data' to turn off eating
The body has evolved two systems - one for turning eating 'on' and one for turning 'off'
A decline in glucose levels in the blood activates the part of the brain called the lateral hypothalamus, resulting in feeling hunger
This causes the individual to search for and consume food, which causes glucose levels to rise
This rise in glucose levels then activates the ventromedial hypothalamus, which leads to feelings of satiation, which in turn inhibits further feeding
Lateral Hypothalamus:
Research in rats has shown damage to the lateral hypothalamus (LH) causes aphagia - an absence of eating
Research has also found that stimulation of the LH causes feeding behaviour
A neurotransmitter found in the hypothalamus, called neuropeptide Y (NPY) is particularly important in turning on eating
WHen injected into the hypothalamus of rats, NPY causes them to immediately begin feeding, even when satiated
Ventromedial Hypothalamus:
Research has shown damage to the ventromedial hypothalamus (VMH) in rats causes hyperphagia (overeating)
Stimulation to the VMH inhibits eating - so the VMH is the 'off' switch in eating
However, damage to the nerve fibres passing through the VMH tends to also damage another part of the hypothalamus, the paraventricular nucleus (PVN)
It's now believed damage to the PVN alone can cause hyperphagia (Gold, 1973)
Neural Control of Cognitive Factors:
Amygdala:
  • The role is thought to be primarily in the selection of foods on the basis of previous experience
  • Rolls and Rolls (1973) found that surgically removing the amygdala in rats would cause the animals to consume both familiar and unfamiliar foods indiscriminately
Inferior Frontal Cortex:
  • Receives messages from the olfactory bulb (part of the brain responsible for smell)
  • Because odours influence the taste of foods, damage to the inferior cortex is thought to decrease eating because of diminished sensory responses to food smell and taste (Kolb and Whishaw, 2006)

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