It should be no surprise that nurturing behaviors cause specific neurochemical actions in the brain.
Biological theories for trichotillomania include a neurochemical imbalance, such as a serotonin imbalance.
Children who are diagnosed with depression should be reassured that the condition is quite common and that it is due to factors beyond their control (i.e., genetics, neurochemical imbalance) rather than any fault of the child.
Others propose that people are genetically predisposed to personality disorders or that they have an underlying biological disturbance (anatomical, electrical, or neurochemical).
Dopamine and other neurochemical transmitters appear to be implicated in bipolar disorder, and these are under investigation as well.