Outline and Evaluate the Role of Neural Mechanisms in Controlling Eating (8 & 16 marks)

Homeostasis is the way in which the brain controls the body’s eating behaviour and keeps levels in our body constant and stable. One theory is that it does this through the dual hypothalamic process which says we have an on switch, Lateral Hypothalamus (LH), and an off switch, ventromedial hypothalamus (VMH), which controls our eating.

The Lateral hypothalamus or ‘feeding centre’ is stimulated to make us feel hungry when our body produces high levels of ghrelin or low levels of either glucose or leptin. If the lateral hypothalamus is damaged then people get aphagia where they do not get hungry and therefore don’t eat. A neurotransmitter called Neuropeptide Y (NPY) is also very important in turning eating on and is found in the hypothalamus. The Ventromedial hypothalamus or ‘satiety centre’ is stimulated to make us feel full when our body produces high levels of glucose or leptin and produces CCK. If this is damaged people get hyperphagia which causes them to not feel full and therefore overeat.

Stellar conducted a study to support the dual hypothalamic process where he stimulated both the LH and the WHM separately in the brains of rats and measuring the amounts of glucose, leptin, ghrelin and CCK in them. He observed that in the rats the LH did in fact turn on hunger and start eating and the VHM make them feel full and stop them eating. This would support neural mechanisms having a role in controlling eating behaviour as the rats eating behaviour changed due to these mechanisms and seemingly nothing else.

Stellar’s study however is lacking in external validity because it was carried out on rats and not humans. It cannot be fully generalised to humans as we have a very different psychological makeup and therefore it cannot be shown that our brain works in the same way as theirs. This is a big weakness in animal studies and reduces how supporting the evidence actually is. However there is a benefit to animal studies as we are allowed to do research on them in ways we would not be allowed to research on humans so they do give us good ideas into topics that we would otherwise have no idea about.

Studying the dual hypothalamic process to show the role of neural mechanisms in controlling eating can be seen to be reductionist as it assumes that the only things influencing eating are the VMH and LH whereas there could be many factors in the body also contributing to it. It would be a better idea to get a more well-rounded view to understand what actually controls eating more fully. However all scientific research does have to be quite specific to establish a cause and effect relationship and therefore saying it is reductionist may be a bit too critical.

Another part of the brain which has been associated with controlling eating is the amygdala which links emotions with food you have previously eaten. Garg et al (2007) did a study to support the fact that emotions and eating are linked by showing 38 participants either a sad movie or a happy movie and observing their eating habits throughout. All participants were given the same amount of popcorn at the start of the movie and how much each person had eaten was measured at the end. It was found that those watching the sad movie ate on average 38% more popcorn than those watching a happy movie. This supports the fact that eating and emotion are linked as the emotion of the participants affected their eating behaviour during the study.

However Garg’s study has many problems with extraneous variables as it is impossible to know the eating habits or emotions of the participants usually and therefore there could have been something other than their emotions effecting what and how they were eating.

Rolls and Rolls (1973) carried out a study to support the role of the amygdala in eating behaviour by surgically removing the amygdala in some rats and leaving it in others then proceeding to give them both familiar and unfamiliar food. They found that the rats with no amygdala would happily consume both sets of food whereas the amygdala-intact rats would consume only the familiar foods. This would support the fact that the amygdala links past experiences to previously eaten foods as those with no amygdala would happily eat any food as they had no past experiences linked to any foods whereas those with an amygdala would only eat the foods they knew and therefore had a past experience with. This study, like Stellar’s, lacks external validity as it was carried out on rats and not humans.