Karl Alexander Deisseroth (born November 18, 1971) is an American scientist and physician. He is the D.H. Chen Foundation Professor of Bioengineering and a professor of psychiatry and behavioral sciences at Stanford University.

He is known for developing the technologies of hydrogel-tissue chemistry (e.g., CLARITY and STARmap) and optogenetics, and for applying integrated optical and genetic strategies to study normal neural circuit function and dysfunction in neurological and psychiatric illnesses.

In 2019, Deisseroth was elected a member of the US National Academy of Engineering for his discoveries and control of neuronal signals underlying animal behavior in health and disease, using molecular and optical tools. He is also a member of the US National Academy of Sciences and the US National Academy of Medicine.

Deisseroth earned a Bachelor of Arts in biochemical sciences from Harvard University in 1992 and an MD–PhD in neuroscience from Stanford University in 1998. He completed his medical internship and psychiatry residency at Stanford University School of Medicine.

Deisseroth has led his laboratory at Stanford University since 2004.^{[citation needed]} He serves as an attending physician at Stanford Hospital and Clinics and has been affiliated with the Howard Hughes Medical Institute (HHMI) since 2009. Between 2014 and 2019, he was a foreign adjunct professor at Sweden's Karolinska Institute.^{[citation needed]}

In 2021, he authored a book titled Projections: A Story of Human Emotions, published by Random House, in which he explored the origins of human emotions through personal encounters with neuropsychiatric patients.

Light-gated ion channels, optogenetics, and neural circuits of behavior

Deisseroth named this field "optogenetics" in 2006 and followed up with the development of optogenetic technologies, leading to many applications, including in psychiatry and neurology. In 2010, the journal Nature Methods named optogenetics "Method of the Year".