Humans like all animals are nature-bound to react against the avoidance of pain, and for the seeking of pleasure, or at the very least the experience of a state of no pain.
The so-called 'hedonic' motivation. Hedonism is the seeking of pleasure and avoidance of pain.
There's a neurotransmitter called 'glutamate' that binds synapses together after a traumatic experience. That is how fear-conditioning and avoidance-learning become hardwired in the brain.
The 'punishment neurons' develop according to experience and remain in place (sometimes for life) unless we manage to override them, for example in cases of some addictions and certain sado-masochistic behaviours.
Another neurotransmitter, called 'GABA', acts to do the opposite to the neurotransmitter called 'glutamate', and works to establish 'reward neurons' when an experience is found to be beneficial. Eating, sex, music, exercise, etcetera.
The brain thus develops diverse pathways that are undoubtedly useful for survival, although as mentioned above, they may be corrupted by other means.
The brain changes in order to allow experience to shape its response then.
It appears also that the brain has a very basic instinctive pain-avoidance capacity but a huge ability to seek reward, via a massive array of potential sources.
For some reason there are those who seek higher and more varied forms and levels of pleasure and those who are less willing or capable of attaining these higher states and are quite content to seek more basic pleasures from drink and drugs or just enjoy a quiet life, for whatever reason.
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