Transcript Hunger ppt. - Ms. Engel @ South

Hunger
Do Now
•
Identify correlations between hunger and other ideas/feelings/motivations
Hunger Drive
• Two areas of
the
hypothalamus,
the lateral and
ventromedial
areas, play a
central role in
the hunger
drive
Hypothalamus
Hypothalamus
Lateral Area
• Electrical lesions to tract of
axons connecting brainstem,
hypothalamus and basal
ganglia cause a loss of all
goal-directed behavior
• Stimulation causes drives in
response to available
incentives
• However, chemical lesions to
specific cell bodies reduce
hunger drive, but do not
abolish it - most other drives
appear normal
– What does this suggest?
Hypothalamus
Hypothalamus
Ventromedial Area
• Lesions alter digestive
and metabolic
processes
• Food is converted into
fat rather than energy
molecules, causing
animal to eat much
more than normal and
gain weight
Hypothalamus
Hypothalamus
• Other stimuli that act on
the brain to increase or
decrease hunger
include
– satiety signals from the
stomach
– signals indicating the
amount of food molecules
in the blood
– leptin, a hormone
indicating the amount of
fat in the body
– the appetizer effect
Hunger Drive
Homeostasis
•
•
Homeostatis and negative feedback governs hunger
– Homeostasis: maintaining state: Thermostat
– Need sufficient calories
• Activation based on anticipation
Why hungry?
– Nutrients: basic components of structural integrity (proteins and amino acids
stored)
– Calories: energy for metabolic processes (glucose, glycogen and fat)
Hungry Hungry Hormones
•
•
•
•
•
Hormone systems work as feedback loop to turn on/off
food seeking or digesting behavior
Insulin: Motivate to seek food when low
– Glucose in system leads to insulin release and tells
body to stop seeking food
– High: about to eat or eating
– Cues (sight/smell) elevate glucose
– Converts glucose to glycogen for storage
Leptin: released by fat when enough NRG is present
(safety valve)
– Injection: eat less
• Mutated mice receive no negative feedback =
overweight
– Increasing leptin does not solve obesity as it
decreases hunger only up to a certain level
PYY: released form intestines when food is present
– Systematic injection: stop eating
• Lower presence of PYY in blood for obese people
than thin. Thin people show a significant increase
in PYY after eating compared to obese people.
Neuropeptide Y: digestive behavior
– Produced by hypothalamus
– Leptin suppress NPY
Research on Weight
Regulation and Dieting
• No consistent personality trait differences found between obese
and non-obese people (e.g., willpower, anxiety)
• Dieters and obese are more likely to eat in response to stress
than non-dieters
• Family environment of little importance in determining body
weight - genetics plays a large role
• Number of fat-storage cells is a major determinant of body
weight
• Settling point (set point) - cluster of genetic and environmental
factors cause a person’s weight to settle within a given range
Research on Weight
Regulation and Dieting
• Fat cells are determined by genetics and food intake
• They increase with weight gain, but merely shrink with
weight loss - may stimulate hunger
• Weight loss causes a decline in basal metabolism
Fat cells
Normal
diet
High-fat
diet
Return to
normal diet
Peripheral Cues for Eating (and Stopping)
-
Full vs. empty stomach
Nutrient level of stomach contents
Glucose levels
Sensory-specific satiety
-
-
Can feel satiated on one type of food but then there is renewed interest in a
different type of food
All of these factors cause signals in specific area of brain (Stellar’s
Dual-Center Hypothesis):
• Lateral Hypothalamus (LH) - Hunger Center (“on switch”)
• Ventromedial Hypothalamus (VMH) -Satiety Center (“off
switch”)
Nisbett (1968) - External hypothesis
• Subjects arrive hungry
• IV-weight of subject (overweight vs. normal)
• IV-quantity of visible food (1 vs. 3 sandwiches)
• Task: Fill out questionnaires
• DV-number of sandwiches consumed
• Hypothesis: If overweight people more sensitive to external cues,
sight of more food should lead obese to eat more, whereas normal
weight people will eat same amount regardless of how much in sight
Results
Interaction Effect
Sandwiches eaten
– Quantity of visible food had no effect on the
eating behavior of normal weight subjects
but for overweight it did. Overweight
subjects ate more when more food was
visible
3
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
Obese
Normal
1 sand
3 sand
Psychology and Dieting
• Rapid loss of weight means rapid return
• Shifting to eating healthier food is more effective
than eating less
• Apply sensory-specific satiety to each a variety of
different healthy foods
• Eat meals slowly as it takes 15 minutes for Leptin
and PYY to start reaching the brain
• Find activities for exercise that you are internally
motivated to perform