Buried deep within the human brain, the neurotransmitters were a network of receptors specifically designed to respond to certain Pieces of Eden that controlled human emotions, thoughts, and behavior.
Created by the Isu and genetically engineered into humanity during its creation as a slave workforce, the neurotransmitters ensured the compliance and docility of humanity for centuries. To ensure this compliance, the Apples of Eden were developed with the explicit purpose of manipulating the neurotransmitter.
Eventually, however, humans began to be born without the neurotransmitter in place; the hybrids – the result of Isu-human interbreeding – were not beholden to the manipulative effects of the Pieces of Eden, and so could challenge the rule of their masters. This eventually led to the outbreak war in 75,010 BCE, with humanity being led by the hybrids Adam and Eve.
The neurotransmitters make an appearance in any and all media featuring humans. Below is listed those appearances where specific mention of the neurotransmitters is made.