Brain Talk: Brain Talk Podcast
View All Brain Talk Podcasts

How Light Affects Our Brain, Our Mood, and Our Sleep
Samer Hattar, Ph.D.
Associate Professor
Department of Biology, School of Arts & Sciences
Department of Neuroscience, School of Medicine

Dr. Samer Hattar

For many years, it was assumed that irregular light cycles influence sleep and circadian rhythms and then cause depression and learning deficits. Here we show that light can directly cause mood and learning changes independent of sleep disruptions or circadian arrhythmicity. We also uncovered that this is not due to vision but to a simple atypical type of photoreceptors in the retina.

Samer Hatter was born in Amman Jordan from a Jordanian father and a Lebanese mother. In his last year of high school, he was introduced to Mendel in Biology class (by an awesome high school teacher) and instantly fell in love with the Science of genetics. He then moved to the north of Jordan to a town called Irbid to study in Yarmouk University majoring in Biology with a minor in Chemistry. After his undergraduate studies, he went to Beirut for a master’s degree in Biochemistry. He was then accepted for graduate studies in Biochemistry at the University of Houston and did his thesis on circadian rhythms with Dr. Arnold Eskin. He then moved for postdoctoral studies at the Salmon Snyder Department of Neuroscience at Johns Hopkins University. It was here where he made his discoveries on the new photosensitive cells in the ganglion cell layer, the ipRGCs. His postdoctoral studies were done in the laboratory of Dr. King-Wai Yau. He established his laboratory at the Department of Biology at Johns Hopkins University in 2004. His laboratory made several important discoveries concerning the pathway by which rods/cones signal light information to non-image functions as well as the effects of light and dark on sleep and alertness. Learn more about Dr. Hattar

Additional Information:

Watch a YouTube video on Dr. Hattar's research

Read "Let There be Light" - an article on

Read "Circadian rhythms: Light hits mood head-on" - an article on

Share This Information