Adjusting the level of self-esteem
It is not always necessary to get the approval or appreciation of others in order to trigger the release of reward neurons. You can do it yourself as well when you appreciate your own views or when you are convinced about yourself. I will give you an example, think about yourself to be a good looking and successful person, and now look into the mirror to get approval. You will now see that you look good, even when other people might not share your point of view. This will, however, lead to an increase of these reward neurons that lead to an increase of self-esteem. You might trap yourself doing this or saying positive things to yourself before going to a party or date.
Placebos work in a similar way. They are effective because we do believe in their effectiveness. Thus whatever we believe in can have a profound impact on our body chemistry and hence on our ability of rational thinking. It also goes the opposite way, whenever you think that something might not work, defense chemicals will be released into your brain which might affect the rational thinking as well and you perceive the feeling of being unsecure. That feeling can become so strong that intense physical reactions such as shaking or a higher heart rate may follow.
So, self-esteem or self-belief is closely linked to the neurotransmitter serotonin. When the lack of it takes on severe proportions, it often leads to depression, self-destructive-behavior and maybe even suicide.