Neural Mechanisms In Eating Behaviour

Question 0

Wickens et al: NPY and Hyperphagia

Answer 0

• found that NPY plays role in stimulating LH and ^appetite.
• Found that damage to LH in rats caused them to stop eating.
• However injected NPY to stimulate LH = eat beyond satiation.
• Rs on Hyperphagia (^hunger ^appetite)shows damaged VmH.
• Exemplifies its involvement of VMH in controlling eating beh.

Question 1

dual center model of appetite regulation

Answer 1

• body uses Homeostasis via 2 control centres;
• lateral and ventromedial hypothalamus respond to BGL.
• LH to ‘turn on’ hunger and VmH is believed to ‘turn off’ hunger.
• Low BGL activate LH resulting in feelings of hunger.
• Eat; VmH activated = feelings of satiety prevent further feasting.
• BGL decrease = hunger increases.

Question 2

Evolutionary exp: refute DCM

Answer 2

• DCM exp suggests hunger mechanism is not adaptive as it reacts to deficits in energy rather than prevents them.
• Evolutionary perspective refutes DCM; we promote levels of consumption which keep us above our optimum in order to buffer against future lack of food.
• Could argue we consume only what we require for short term to prevent fat storage.
• Ensure flexibility and agility making hunting easier in our EEA (evolutionary environment of adaptiveness).

Question 3

DCM reductionist

Answer 3

• LH damage also causes deficit in thirst and sex drive.
• Neural circuits throughout brain play a role in EB not just hypo.
• F rats still felt satiety if VMH is removed/hunger when LH removed.
• As hunger and satiety were unaffected assumed the model is OS.
• However rat R should be GWC to humans there are marked differences in our comparative neuro-anatomies.
• Appears to be more complex process occurring.

Question 4

Further evidence of OS:(rats bio rhythms)

Answer 4

• Clear that various signals sent to the hypothalamus via complex mechanisms (be it neural or hormonal).
• Therefore possible other mech ie bio rhythms also play a part.
• e.g. rats active & display EB as darkness descends which is influenced by the suprachiasmatic nucleus another region of the hypothalamus.

Question 5

Leptin model

Answer 5

• Leptin is produced by fat tissue & secreted into the blood stream.
• Causes fat loss and decreased appetite.
• Leptin signals to VmH amount of stored fat which in turn regulates long term body weight.

Question 6

Zhang et al: Defective rats

Answer 6

• Some rats with defective gene inhibiting Leptin release = obese.
• Injecting these rats with Leptin resulted in them losing weight.
• Genetic differences may also lead to hormonal imbalance and affect EB.

Question 7

Leptin’s deficiency in humans

Answer 7

• Rare cases of Leptin’s deficiency in humans.
• Evidence to prove Leptin does influence EB.
• Some people can’t control their EB and become obese
• But Leptin injections help them to lose weight.
• Leptin model provides RWTI for obesity, which could save millions for the NHS

Question 8

Leptin insensitivity

Answer 8

• For most obese people Leptin is an ineffective treatment
• as hypothalamus develops insensitivity.
• Argued more research is necessary for a full understanding of this model as an explanation for EB.