A Penn faculty member since 1989, Dr. Clark spent most of his career studying Alzheimer's disease, the website states.
He was "the current principal investigator of a National Institute on Aging grant, and an investigator for numerous other studies including the landmark Alzheimer's Disease Neuroimaging Initiative," according to the website.
Karlawish wrote that "he had a particular commitment to developing efficient methods for the early and reliable diagnosis of Alzheimer's disease that could be readily adopted into routine primary-care clinical practice."
Dr. Clark, with Douglas Eubanks at Penn, "codeveloped the Dementia Severity Rating Scale, a self-administered scale that a family member could complete and whose scores assisted in diagnosing dementia and mild cognitive impairment."
After retiring from Penn, Karlawish wrote, Dr. Clark was medical director for Avid Radiopharmaceuticals, a subsidiary of Eli Lilly & Co.
His research at the firm, "published in the Journal of the American Medical Association in 2011, is regarded as being a landmark study for advancing clinically applicable Alzheimer's disease diagnostics," Karlawish wrote.
Born in Norfolk, Va., Dr. Clark earned a bachelor's degree in animal science at Pennsylvania State University in 1968 and graduated in 1973 from what is now Jefferson Medical College at Thomas Jefferson University.
He studied neurology at Pennsylvania Hospital and completed his residency in 1977 at the Neurological Institute of New York, at what is now Columbia University Medical Center in New York City.
He then worked in the neurology department at Pennsylvania Hospital.
From 1985 until 1989, when he joined the Penn faculty, Dr. Clark was director of the Memory Disorders Clinic and clinical director of the Joseph and Kathleen Bryan Alzheimer's Disease Research Center at Duke University.
On trips to Ireland and France, Dr. Clark showed his sense of horseback adventure with open country riding and fence jumping.
Dr. Clark is survived by his wife, Anne; stepsons David and Matthew Emrich; a brother; and a sister.
A memorial service was set for 6 p.m. Thursday, Jan. 19, in the Jordan Lobby at the Franklin Institute.
Contributions, payable to Trustees of the University of Pennsylvania, may be made to the Penn Memory Center/Institute on Aging, 3535 Market St. Philadelphia 19104-3309.
Contact staff writer Walter F. Naedele at 215-854-5607 or firstname.lastname@example.org.