Daytime Light Important For Brain Health

MedicalResearch.com Interview with:

Dr. Lily Yan MD PhD Department of Psychology & Neuroscience Program Michigan State University East Lansing, MI 48824 

Dr. Lily Yan

Dr. Lily Yan MD PhD
Department of Psychology & Neuroscience Program
Michigan State University
East Lansing, MI 48824 

MedicalResearch.com: What is the background for this study? What are the main findings?

  • The effects of light on cognitive function have been well-documented in human studies, with brighter illumination associated with better cognitive performance. However, the underlying neural mechanisms are not well understood.
  • In this study, we explored the mechanisms of how light modulates spatial learning and memory, using diurnal Nile grass rats. In contrast to most laboratory animals that are active at night and fall asleep following light exposure, these animals are active during the day, thus an ideal model for understanding the effects of light on humans.
  • When the animals were housed in dim light during the day, mimicking the cloudy days or typical indoor lighting, the animals had a ~30% reduction in the dendritic spines, which make the connection between brain cells, within the hippocampus, a brain region critical for learning and memory. Animals housed in dim light also performed poorly in a water maze, compared to those housed in bright light.
  • When the animals that had been in dim light were then housed in bright light for 4 weeks, the connections in their hippocampus and performance in the water maze recovered fully. 

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Daytime Bright Light May Reduce Adverse Sleep Effects of Blue Light At Bedtime

MedicalResearch.com Interview with:

Frida Rångtell PhD Student Department of Neuroscience, Division of Functional Pharmacology Uppsala University, Sweden

Frida Rångtell

Frida Rångtell PhD Student
Department of Neuroscience, Division of Functional Pharmacology
Uppsala University, Sweden

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: Previous studies have demonstrated that evening use of electronic devices emitting blue light, e.g. tablet computers, increases time to fall asleep, reduces the quality of slow-wave sleep (a sleep stage that has for instance been shown to boost memory consolidation and immune functions), and decreases the time in rapid eye movement sleep (which has been proposed to play a role in emotional regulation and consolidation of emotional memories). One explanation could be the blue light-mediated suppression of the sleep-promoting hormone melatonin. Blue LED Warehouse or bedroom lights have a much lower effect on this because they are not shining straight into the viewer’s eyes, like phone LEDs.

In the current experiment however, after 6.5 hours of constant bright light exposure during the day, there were no effects on sleep or melatonin levels after reading a traditional book versus the same book on a self-luminous tablet for two hours before bedtime. Even though the light from the self-luminous tablet was enriched in blue light. Our null findings may at first glance appear surprising, especially in light of previous epidemiological findings linking the use of electronic devices before bedtime with sleep disturbances.

One plausible explanation for these discrepant results across experiments, in our view, is that bright light exposure during daytime – similar to that employed in the present study (~570 lux over 6.5 hours prior to evening light stimulation) – has previously been shown to attenuate the suppressive properties of evening light exposure on melatonin levels.

Our results could therefore suggest that light exposure during the day, e.g. by means of outdoor activities or light interventions in offices, may help combat sleep disturbances associated with evening blue light stimulation. Finally, it must be borne in mind that reading is generally considered to be a cognitively demanding task. Thus, it could be speculated that evening reading may contribute to greater sleep pressure, which may have hampered our ability to detect differences in sleep between the tablet reading and physical book reading conditions. A recent study involving young children has for instance demonstrated that reading at bedtime is associated with improved sleep, as indicated by longer total nocturnal sleep duration.

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