Study of the development and function of the nervous system, with emphasis on how nerve cells generate and control behavior. The major goal of neurobiology is to explain at the molecular level how nerve cells differentiate and develop their specific connections and how nerve networks store and recall information. Ancillary studies on disease processes and drug effects in the nervous system also provide useful approaches for understanding the normal state by comparison with perturbed or abnormal systems. The functions of the nervous system may be studied at several levels: molecular, subcellular (organelle), cellular, simple multicellular interacting systems, complex systems, and higher functions (whole animal behavior).