The present invention provides methods to modulate key elements along the DAG signaling pathway as well as a diagnostic assay, device and methods of using the same to diagnose bipolar disorder (BD) and attention deficit hyperactivity disorder (ADHD). Methods to identify diagnostic markers and drug targets for BD and ADHD. Methods of identifying effective compounds responsible for membrane potentials and excitabilities influencing bipolar disorder (BD) and attention deficit hyperactivity disorder (ADHD). Methods of identifying an effective compound that modulates the activity of Ca2+/CaM enzyme and compounds involved in changing the K+ gradient across the plasma membrane thereby increasing or decreasing the membrane potential ratio (MPR™) values. The invention provides methods of identifying a compound that modulates the activity of PKC which is an important protein of the DAG signaling pathway. Methods of identifying a compound that modulates DAG and its related enzymes along the DAG signaling pathway are p
