Trainee Profile

Division of Sleep Medicine, Brigham and Women's Hospital

Dr. Santhi’s research focuses on the impact of adverse circadian phase and extended wakefulness on cognitive processes, and more specifically, on investigating the interaction of circadian and attentional variables. Lapses of attention and cognitive failures are implicated in a wide range of accidents associated with extended wakefulness and/or adverse circadian phase (e.g. single vehicle automobile accidents, the accident at the Three Mile Island nuclear power plant, the Exxon Valdez grounding).  Studies have indicated that such attentional lapses and failures are more frequent at adverse circadian phase (especially during night shift work) or under conditions of extended wakefulness.  One of the goals of Dr. Sathi’s current research is to examine the impact of rotating and night shift work on cognitive performance. Previous research indicates that treating night shift workers with appropriately timed bright light can induce rapid circadian adaptation to the night shift. However, it is not known whether such treatments are indeed successful in alleviating reduced attentional capacity associated with night work. A second goal of Dr. Santhi’s research is to evaluate the effectiveness of appropriately timed bright light in preventing the lowering of attentional capacity during night shift work. Dr. Santhi is also investigating the resetting effects of light on the human circadian pacemaker. The daily alternation of light and darkness is the most important periodic environmental stimulus for entraining human circadian rhythms. The sensitivity of the circadian pacemaker to light is assessed by measuring the resetting of the circadian pacemaker to a light stimulus. This research project tests the hypothesis that light exposure causes phase advances and delays of the human circadian system in a duration-dependent manner, with larger phase shifts caused by exposure to longer duration light.

Charles A. Czeisler, PhD, MD; Jeanne Duffy, MBA, PhD;

Santhi N & Reeves A (2004): The roles of distractor coherence and target certainty in visual search:  A signal detection model.
Vision Research, Volume 44 (12), pp 1235-1256

Reeves A, Santhi N, & DeCaro SA (2005): A random ray model for speed and accuracy in perceptual experiments.
Spatial Vision. Volume 18 (1), pp 73-83

Santhi N, Duffy JF, Horowitz TS, & Czeisler CA (in press): Scheduling of Sleep/Darkness Affects the Circadian Phase of Night Shift Workers.
Neuroscience Letters.