An implicit premise in neuropsychopharmacology with regard to the psychological aspects is that all states of mind, including both normal and drug-induced altered states, and diseases involving mental or cognitive dysfunction, have a neuro-chemical basis at the fundamental level, and certain circuit pathways in the central nervous system at a higher level. (See also: Neuron doctrine) Thus the understanding of nerve cells or neurons in the brain is central to understanding the mind. It is reasoned that the mechanisms involved can be elucidated through modern clinical and research methods such as genetic manipulation in animal subjects, imaging techniques such as functional magnetic resonance imaging (fMRI), and in vitro studies using selective binding agents on live tissue cultures.