Neural mechanisms in Eating Behaviour

Neural mechanisms in Eating Behaviour

1. Homeostasis

   • A01
     • Involves mechanisms which keep our bodies balanced
       • In equilibrium
     • When glucose levels drop hunger increases + we look for food
       • Once G levels rise we feel satisfied + stop eating
         • There is a time lag between stimuli + mechanism but body can account for that
   • A02
     • Limitations
       • Theory can be viewed as incompatible w/ evol. of hunger mechanisms
         • In order for it to be adaptive it must both anticipate + prevent hunger (energy deficits)
       • Doesn't make sense for eating + hunger to be triggered once energy levels are below their desired amount

2. Lateral hypothalamus

   • A01
     • When G levels in blood get low LH is triggered causing hunger + makes someone go in search of food
     • NPY = neurotransmitter found in LH important for eating
   • A02
     • Problems w/ LH
       • A few probs. have been identified w/ idea LH acts as 'on switch' for eating
         • Damage causes deficits in other aspects of behaviour (thirst + sex) rather than just hunger
       • Sakurai et al
         • Found eating behaviour is controlled by neural circuits all over brain
           • Meaning while LH probably still plays important role it isn't 'eating centre' as initially believed
     • Problems w/ NPY
       • Recent research has cast doubt on whether neuropeptide Y's normal function is to influence feeding
         • Marie et al
           • Genetically manipulated mice so that they didn't make NPY
             • Found no subsequent decrease in feeding behaviour
               • Suggest hunger stimulated by injections of NPY may be an experimental artefact
     • IDA - Real-world application
       • Yang et al
         • Found NPY is produced by abdominal fat + suggest this leads to vicious cycle where NPY produced in brain leads to more eating + production of more fat cells, leading to more NPY + fat cells + so on
           • By targeting those at risk they believe it should be poss. to treat them w/ drugs that turn off NPY + this prevent obesity

3. Ventromedial hypothalamus

   • A01
     • Part of H responsible for saying when someone's satisfied after food due to lots of G receptors
     • Damage to this area causes overeating (hyperphagia) due to fact person no longer 'knows' when their full
   • A02
     • Research for VMH
       • Early research found damage to VMH led to hyperphagia + obesity in a no. of species, including humans
         • Led to VMH being named 'satiety centre'
       • However...
         • Gold
           • Found lesions restricted to VMH alone didn't result in hyperphagia + only produced overeating when other areas (paraventriculeur nucleus) is also damaged
             • Subsequent research has failed to replicate Gold's findings

4. Cognitive factors

   • A01
     • Amygdala + inferior pre-frontal cortex are responsible for cognitive aspects of hunger
       • Amygdala means we choose food based on our experience of that food
         • If you remove amygdala = rats eat novel + familiar foods (when they would usually avoid novel food)
           • Rolls + Rolls
     • Messages to IPFC come from part of brain responsible for smell (olfactory bulb) meaning if IPFC is damaged there is a decrease in eating
   • A02
     • Research support
       • Zald + Pardo
         • Provide psychological evidence to support claim amygdala participates in emotional processing of olfactory stimuli
           • Exposed healthy adult ppts to aversive olfactory stimuli while measuring blood flow to amygdala via PET scan
             • Were significant blood flow increases to A when ppts where exposed to unpleasant smells
     • Kluver-Bucy syndrome
       • Damage to amygdala + IPFC could explain feeding abnormalities observed in K-B syndrome
         • Patients typically show increased appetite, indiscriminate eating + even attempt to eat non-food items
         • Research suggests food cues no longer accurately represent their real reward value to indivi.
     • IDA - Evol. approach
       • Evol. theorists suggest primary stimuli for hunger + eating is foods positive-incentive value
         • People eat because they develop a relish for particular tastes that are associated w/ foods that promote our survival