Brain and behavior disorders are increasingly considered to be caused by altered functioning in the circuitry of the brain. Now known to be a vast and sophisticated network, the circuitry of the brain has proven elusive for scientists attempting to understand its ‘language’ and correct its dysfunction. A great step forward was made in 2005 when Karl Deisseroth, M.D., Ph.D., of Stanford University used his NARSAD Young Investigator Grant to invent optogenetics. Optogenetics is a new technology that uses light to make neurons fire one at a time, giving researchers extraordinary control over specific brain circuits in living animals. Thanks to optogenetics, neuroscientists can go beyond observing correlations between the activity of neurons and an animal’s behavior; by turning particular neurons on or off at will, they can prove that those neurons actually govern the behavior.

A recent special issue of Biological Psychiatry was dedicated to understanding the impact of optogenetics on psychiatry. Now in use at over 1,000 laboratories, this method is enabling the identification of the mechanisms that give rise to depression, anxiety, post-traumatic stress disorder and other brain and behavior disorders. Thomas R. Insel, M.D., Director of the National Institute of Mental Health, wrote in a commentary in the publication: “Understanding the circuitry underlying mental disorders is a daunting task but one that becomes more attainable with each new discovery about the complex circuits involved in behavior. Optogenetics has revolutionized systems neuroscience by providing precise control over circuitry in awake, behaving animals.” This is the exciting part of optogenetics—the control over defined events within defined cell types at defined times and the ability to observe the resulting behavior in animals—that offers a new level of precision necessary to identifying the biology of brain and behavior disorders.

Dr. Deisseroth looks forward in his introductory comments in the special issue, stating that, “Optogenetic tools provide experimental leverage leading to insights into neural circuit function and dysfunction that are impossible to establish by other means … this approach must be integrated well with existing sophisticated psychiatric disease-model research methods spanning behavior, psychology, imaging, electrophysiology, pharmacology, and genetics. Additional technologies also need to be developed further for this approach to reach its full potential.”