Honors & Awards

  • Postdoctoral Research Scholarship, French Society of Research in Sleep Medicine (SFRMS) (July 18, 2014)
  • Research Merit Award, Society for Research on Biological Rhythms (SRBR) (June 13, 2014)
  • Excellence Award, Sleep Research Society (SRS) (June 1, 2014)
  • Research Merit Award, Society for Research on Biological Rhythms (SRBR) (May 19, 2012)
  • Research Scholarship, French Federation of the Blind and Visually Impaired (FAF) (Oct 10, 2011)
  • Research Scholarship, French Society of Research in Sleep Medicine (SFRMS) (Sep 2011 (Declined))
  • Short Oral Communication Prize, XII. Congress of the European Biological Rhythms Society (EBRS), Oxford (Aug 20-26, 2011)
  • Poster Prize, XI. Congress of the European Biological Rhythms Society (EBRS), Strasbourg (Aug 22-28, 2009)
  • Research Scholarship, Ministère de l Enseignement Supérieur et de la Recherche Français (July, 2008)
  • Graduate Assistantship, American University of Beirut (AUB) (Aug, 2007 (Declined))
  • Honor Award, Lebanese University, Faculty of Sciences II (June, 2007)

Professional Education

  • Ph.D, Claude Bernard University - Lyon 1, Neuroscience (2012)
  • Master of Science, Claude Bernard University - Lyon 1, Neuroscience (2008)
  • Bachelor of Science, Lebanese University Faculty of Sciences II, Physiology (2007)

Stanford Advisors

Journal Articles

  • Chronic artificial blue-enriched white light is an effective countermeasure to delayed circadian phase and neurobehavioral decrements. PloS one Najjar, R. P., Wolf, L., Taillard, J., Schlangen, L. J., Salam, A., Cajochen, C., Gronfier, C. 2014; 9 (7): e102827


    Studies in Polar Base stations, where personnel have no access to sunlight during winter, have reported circadian misalignment, free-running of the sleep-wake rhythm, and sleep problems. Here we tested light as a countermeasure to circadian misalignment in personnel of the Concordia Polar Base station during the polar winter. We hypothesized that entrainment of the circadian pacemaker to a 24-h light-dark schedule would not occur in all crew members (n = 10) exposed to 100-300 lux of standard fluorescent white (SW) light during the daytime, and that chronic non-time restricted daytime exposure to melanopsin-optimized blue-enriched white (BE) light would establish an a stable circadian phase, in participants, together with increased cognitive performance and mood levels. The lighting schedule consisted of an alternation between SW lighting (2 weeks), followed by a BE lighting (2 weeks) for a total of 9 weeks. Rest-activity cycles assessed by actigraphy showed a stable rest-activity pattern under both SW and BE light. No difference was found between light conditions on the intra-daily stability, variability and amplitude of activity, as assessed by non-parametric circadian analysis. As hypothesized, a significant delay of about 30 minutes in the onset of melatonin secretion occurred with SW, but not with BE light. BE light significantly enhanced well being and alertness compared to SW light. We propose that the superior efficacy of blue-enriched white light versus standard white light involves melanopsin-based mechanisms in the activation of the non-visual functions studied, and that their responses do not dampen with time (over 9-weeks). This work could lead to practical applications of light exposure in working environment where background light intensity is chronically low to moderate (polar base stations, power plants, space missions, etc.), and may help design lighting strategies to maintain health, productivity, and personnel safety.

    View details for DOI 10.1371/journal.pone.0102827

    View details for PubMedID 25072880

  • Aging of non-visual spectral sensitivity to light in humans: compensatory mechanisms? PloS one Najjar, R. P., Chiquet, C., Teikari, P., Cornut, P. L., Claustrat, B., Denis, P., Cooper, H. M., Gronfier, C. 2014; 9 (1): e85837


    The deterioration of sleep in the older population is a prevalent feature that contributes to a decrease in quality of life. Inappropriate entrainment of the circadian clock by light is considered to contribute to the alteration of sleep structure and circadian rhythms in the elderly. The present study investigates the effects of aging on non-visual spectral sensitivity to light and tests the hypothesis that circadian disturbances are related to a decreased light transmittance. In a within-subject design, eight aged and five young subjects were exposed at night to 60 minute monochromatic light stimulations at 9 different wavelengths (420-620 nm). Individual sensitivity spectra were derived from measures of melatonin suppression. Lens density was assessed using a validated psychophysical technique. Although lens transmittance was decreased for short wavelength light in the older participants, melatonin suppression was not reduced. Peak of non-visual sensitivity was, however, shifted to longer wavelengths in the aged participants (494 nm) compared to young (484 nm). Our results indicate that increased lens filtering does not necessarily lead to a decreased non-visual sensitivity to light. The lack of age-related decrease in non-visual sensitivity to light may involve as yet undefined adaptive mechanisms.

    View details for DOI 10.1371/journal.pone.0085837

    View details for PubMedID 24465738

  • Age-Related Changes in Circadian Rhythms During Adulthood The Encyclopedia of Sleep Daneault V, Vandewalle G, Najjar RP, Mongrain V, Dumont M, Hebert M, Carrier J. 2013; 3: 113-117
  • An inexpensive Arduino-based LED stimulator system for vision research JOURNAL OF NEUROSCIENCE METHODS Teikari, P., Najjar, R. P., Malkki, H., Knoblauch, K., Dumortier, D., Gronfier, C., Cooper, H. M. 2012; 211 (2): 227-236


    Light emitting diodes (LEDs) are being used increasingly as light sources in life sciences applications such as in vision research, fluorescence microscopy and in brain-computer interfacing. Here we present an inexpensive but effective visual stimulator based on light emitting diodes (LEDs) and open-source Arduino microcontroller prototyping platform. The main design goal of our system was to use off-the-shelf and open-source components as much as possible, and to reduce design complexity allowing use of the system to end-users without advanced electronics skills. The main core of the system is a USB-connected Arduino microcontroller platform designed initially with a specific emphasis on the ease-of-use creating interactive physical computing environments. The pulse-width modulation (PWM) signal of Arduino was used to drive LEDs allowing linear light intensity control. The visual stimulator was demonstrated in applications such as murine pupillometry, rodent models for cognitive research, and heterochromatic flicker photometry in human psychophysics. These examples illustrate some of the possible applications that can be easily implemented and that are advantageous for students, educational purposes and universities with limited resources. The LED stimulator system was developed as an open-source project. Software interface was developed using Python with simplified examples provided for Matlab and LabVIEW. Source code and hardware information are distributed under the GNU General Public Licence (GPL, version 3).

    View details for DOI 10.1016/j.jneumeth.2012.09.012

    View details for Web of Science ID 000312753500007

    View details for PubMedID 23000405

  • Refined flicker photometry technique to measure ocular lens density JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION Teikari, P., Najjar, R. P., Knoblauch, K., Dumortier, D., Cornut, P., Denis, P., Cooper, H. M., Gronfier, C. 2012; 29 (11): 2469-2478


    Many physiological and pathological conditions are associated with a change in the crystalline lens transmittance. Estimates of lens opacification, however, generally rely on subjective rather than objective measures in clinical practice. The goal of our study was to develop an improved psychophysical heterochromatic flicker photometry technique combined with existing mathematical models to evaluate the spectral transmittance of the human ocular media noninvasively. Our results show that it is possible to accurately estimate ocular media density in vivo in humans. Potential applications of our approach include basic research and clinical settings on visual and nonimage-forming visual systems.

    View details for Web of Science ID 000310590500028

    View details for PubMedID 23201811