21 Feeding and Eating

Question 1

What are the two metabolic states?

Answer 1

Catabolic - releasing and using energy, associated with weight loss
Anabolic - acquiring and storing energy, associated with weight gain

Question 2

What can lipectomies in Siberian hamsters teach us about body weight?

Answer 2

Hamsters put weight back on almost immediately after lipectomy - which has only temporary effect on seasonal weight cycle. This suggests there is a set point of ideal weight, which regulates catabolic and anabolic systems.

Question 3

What are the FIVE main hunger and satiety signals from the body?

Answer 3

1. Stomach stretch
2. Blood sugar
3. Leptin
4. Ghrelin
5. Insulin

Question 4

How does stomach stretch send satiety signals to brain?

Answer 4

Stomach stretch is picked up by the somatosensory nerve and sent to nucleus of the solitary tract (NTS) in the medulla.

Question 5

How does blood sugar send signals to brain?

Answer 5

Blood sugar is picked up by sugar-sensitive cells in the NTS

Question 6

How do Leptin signals reach the brain?

Answer 6

Leptin is picked up by arcuate nucleus (ARC) of the hypothalamus. More leptin is produced when there is more body fat, sign to stop eating.

Question 7

When is Ghrelin produced and what does it do?

Answer 7

Ghrelin – produced when stomach is empty – picked up by ARC. Spike in Ghrelin precedes eating.

Question 8

What does Insulin tell the brain?

Answer 8

Insulin is picked up by ARC and indicates there is enough blood sugar.

Question 9

What does the lateral hypothalamus (LH) do?

Answer 9

The lateral hypothalamus stimulates energy conservation “orexic” - seeking and storing food

Question 10

How does the ARC operate in regards to the LVN and LH?

Answer 10

It switches them on or off.

Question 11

If ghrelin picked up by ARC, what happens?

Answer 11

LH is stimulated and PVN is inhibited -> orexic state

Question 12

If leptin or insulin picked up by ARC, what happens?

Answer 12

Leptin and insulin cause the ARC to inhibit the LH and stimulate the PVN

Question 13

What does the paraventricular nucleus (PVN) of the hypothalamus do?

Answer 13

The paraventricular nucleus stimulates energy consumption “anorexic” - projects to pituitary gland, involved in fight-or-fight response

Question 14

How does the PVN affect the autonomic nervous system?

Answer 14

The PVN sends signals to the medulla, stimulating the parasympathetic nervous system

Question 15

What is the difference between wanting and needing food?

Answer 15

Our appetite for food is only vaguely related to our need for energy.

HOWEVER,

• We can crave food when we’re sated.
• Starved people are not necessarily hungry
• Terminating meals has little to do with how many calories we’ve eaten

Question 16

What is the role of the mesolimbic dopamine system in appetite?

Answer 16

The mesolimbic DA system is activated by food cues. Food causes spike in DA release in nucleus accumbens.

In conditioning experiments, DA released in nucleus accumbens upon presentations of CS associated with food, rather than food itself. DA in nucleus accumbens is linked to salience of reward, not to sensory pleasure of it.

In the obese, this happens even when sated. Obese are also more sensitive to external sensory cues – more DA released.

Question 17

What role does the orbitofrontal cortex have in appetite?

Answer 17

It regulates the pleasure of eating food once satiety is reached. Craving a food increases pleasure; satiety decreases pleasure in eating. OFC contains pleasantness/satiety switch. In obese people this switch isn’t working so well – continue eating and finding food pleasant.

Question 18

How does DA spike in nucleus accumbens affect LH?

Answer 18

NAc connects to LH which connects to VTA which connects to NAc which connects to cortex to drive behaviour. So when you get DA spike from seeing food, LH is stimulated (orexic state) and cortex is spurred to act.

Question 19

What distinction does Schachter (1971) make between types of food-relevant cues?

Answer 19

Internal cues of hunger and satiety

External food or meal relevant cues - these can increase appetite, regardless of internal cues (cookie smell in waiting room example)

Question 20

How, according to Schachter, does the reaction of obese people to these cues differ from that of the non-obese?

Answer 20

Obese are less sensitive to internal cues, more sensitive to external cues

Question 21

What additional distinction did Herman and Polivy (2008) add?

Answer 21

External cues should be divided into -

Normative cues - eg. how much on plate, when others stop eating

Sensory cues - smells, taste, look of food

Obese people specifically sensitive to sensory cues

Question 22

How does the behaviour of obese people in all-you-can-eat buffets differ from that of lean people?

Answer 22

Obese people pile up heaps of food, sit facing buffet. Sensitivity to sensory cues makes food taste better if exposed to more of it. And more likely to refill plate.

Question 23

What’s the difference between wanting a food and liking it?

Answer 23

Wanting it means now; liking means in general.

Question 24

What additional distinction did Herman and Polivy (2008) add?

Answer 24

External cues should be divided into -

Normative cues - eg. how much on plate, when others stop eating

Sensory cues - smells, taste, look of food

Obese people specifically sensitive to sensory cues

Question 25

How does the behaviour of obese people in all-you-can-eat buffets differ?

Answer 25

Obese people pile up heaps of food, sit facing buffet. Sensitivity to sensory cues makes food taste better if exposed to more of it. And more likely to refill plate.

Question 26

What’s the difference between wanting a food and liking it?

Answer 26

Wanting it means now; liking means in general.

Question 27

How do rats’ hedonic reactions to salt change over level of depletion?

Answer 27

The more depleted in salt the rats are, the more they show hedonic response, and less aversive response (gaping).

Question 28

What evidence is there that the satiety/pleasantness switch isn’t working in obese people?

Answer 28

They continue eating after satiety and continue finding food pleasant.

Question 29

What effect does food palatability have on food consumption?

Answer 29

Highly palatable foods decrease effect of satiety on consumption - they disguise effect of satiety. (Palatable foods also tend to be energy dense.)

Question 30

What role does the orbitofrontal cortex have in appetite?

Answer 30

It regulates the pleasure of eating food once satiety is reached. Craving a food increases pleasure; satiety decreases pleasure in eating. OFC contains pleasantness/satiety switch.

Question 31

What evidence is there that the satiety/pleasantness switch isn’t working in obese people?

Answer 31

They continue eating after satiety and continue finding food pleasant.

Question 32

What effect does food palatability have on food consumption?

Answer 32

Highly palatable foods decrease effect of satiety on consumption - they disguise effect of satiety. Palatable foods also tend to be energy dense.