Biological explanations to
Role of neural mechanisms
Answer the following -
• Did you have breakfast this morning?
• Why did you stop eating the food?
• What are your favourite foods? Why?
• How do you feel after a large meal?
Role of neural mechanisms
in eating behaviour
• Eating behaviour = ingestive behaviour
– if we are hot – we sweat
– if we are dehydrated – thirsty
– If we need food – hunger
• Homeostasis is maintained via a negative feedback
loop: this assumes that all body variables have a set
point (or range)
• The digestive tract and the hypothalamus play a
significant role in homeostasis in eating behaviour.
The process by which the
body maintains a constant
• Involves mechanisms that can detect and correct.
• Detect – check whether the body has enough
nutrients (internal environment)
• Correct – restore the body to its optimal state.
• Body evolved 2 separate systems in order to cope
with the time lag between restoring equilibrium and
body registering their effect.
• Turning eating on and turning eating off!
Decrease in glucose
As glucose levels decrease hunger levels increase
Increase in glucose levels means satiation reached.
Activates this area – feel
food and eats
Increase in glucose
Activates this area –
feeling of satiation –
inhibits further feeding
• Each individual has a set point and their
weight is regulated around that set point
• Body regulates hunger based possibly on
– Fat stores
– Glucose levels
– Cellular energy
Dual-Centre Theory of feeding
• 2 areas of the hypothalamus involved in
– Ventro Medial Hypothalamus (VMH) as a "satiety
centre" = full up!
– Lateral Hypothalamus (LH) as a "Hunger centre".
• NOTE: VMH and LH are also called VMN and
The lateral hypothalamus
• Contains the
• This initiates eating.
• It responds to
increase in ghrelin a
from the stomach
when it is empty.
• Contains the satiety
• This inhibits eating
behaviour when we are
• Responds to
– an increase in blood
– a decrease in ghrelin and
to release of CCK, a
hormone released when
food is detected in the
– leptin a long term satiety
signal released by fat
The hypothalamus – research
evidence comes from…
• Case studies -patients with tumours in the
hypothalamus tend to become obese
• Methods used to research hypothalamus
– Lesioning in animals
– Investigation of feeding
patterns after brain damage
– Effects of neurotransmitters
introduced into parts of brain
– Impact of drugs on eating
– Use of fMRI (Functional
Role of hypothalamus - evidence
• Aphagia (failure to eat when hungry) can be
caused by damage to the LH.
• Rats whose VMH had been lesioned developed
overeating and obesity
• Wickens (2000) Rats: Injected with NPY = became
• However, Gold (1973) found that lesions
restricted to the VMH alone did NOT result in
hyperphagia and only produced overeating when
they included other areas.
Hetherington and Ranson (1942)
The VMH Rat
Made lesions on an area of the VMH
(part of the hypothalamus) in rats.
Caused the rats to overeat and be
This lesion destroyed a centre that
is vital for the control of feeding
behaviour. Its destruction led to an
increase in feeding and body weight.
It was assumed that this was a
satiety centre – which is normally
activated when the animal is full at
the end of the meal.
Satiety – the feeling or
state of being fully
satisfied. Satiety centres
function is to stop feeding
The role of the hypothalamus -
Is it really the ‘ON’ switch??
Damage to LH also affects thirst and sex drives.
Recent research suggests eating is more widely
It is thought that the hypothalamus plays a role but
it is not solely responsible
Ao2 Role of ghrelin - evidence
• Cummings (2004) monitored PPs’ ghrelin levels every 5 minutes
• PPs had to assess their level of hunger every 30 mins.
• In 5 of the 6 participants there was a significant correlation between
ghrelin levels, emptiness of the stomach and hunger.
• The results support the theory of the role of ghrelin in eating
• In addition ghrelin injections result in increased food intake in
• Gastric bands used in treating obesity reduce ghrelin secretion.
• However: The study used a small sample limiting how far the
findings can be generalised.
• It is likely that the participant’s subjective judgements of hunger
were influenced by expectations of food based on meal times
(cultural factors rather than biological factors)
Role of neurotransmitters
that increase food intake
• Neuropeptide Y–Rats injected with neuropeptide Y
continue eating large amounts of food even
– It also seems to cause a preference for carbohydrates
Ao2 Supporting evidence:
Marie et al (2005)
role of neuropeptide Y
• Injections of NPY in mice cause hunger...
Genetically manipulated mice so that they did
not produce neuropeptide Y. Found no
subsequent decrease in their feeding
Neurotransmitters and modulators
that decrease food intake
• (CCK) –released into bloodstream during meals
– Causes reduction in appetite.
– Suppresses weight gain
Evaluation of neural mechanisms and
++Insight into brain chemicals – could be used to develop
medical interventions to help change what we eat
+Provides explanation of some differences in eating behaviour
+Studies such as those involving lesions to the LH and VMH in
rats have supported the role of the hypothalamus in
regulating eating behaviour
+Studies involving electrical stimulation of these centres have
confirmed their role in feeding and satiety.
+Such studies provide sound scientific evidence but there is
the issue of extrapolating finding from rats to humans.
• Cumming et al, 2004 - ghrelin
-Reductionism: focus exclusively on biological aspects of hunger and
-Biological determinism: focus exclusively on the role of nature and no
space left to choice and cultural and social influences
-there is substantial and convincing evidence that social, cultural and
psychological factors affect our eating behaviours as is evident from
psychological explanations of eating disorders
-Use of animals in research implies a lack of generalisability- we must
be cautious of findings
-Highly controlled lab experiments may lack ecological validity
-Physiological drives can be overriden (eg desire to lose weight; dislike
of certain foods; fear of losing control; social cues to continue
eating; food availability)
• Ethical issues with non-human animalsissues
• Is the biological approach reductionist?
• Free will vs determinism (can biological drives
• You contrast explanations to eating behaviour
• Learning (Behaviourist)