Impacts of Short Wavelength Light on Cortical Excitability

1246 

Abstract Submission 

Roya Sharifpour¹, Fermin Aizpurua¹, Ilenia Paparella¹, Islay Campbell¹, Elise Beckers¹, Nasrin Mortazavi¹, Ekaterina Koshmanova¹, Christophe Phillips², Gilles Vandewalle¹

¹Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège, Liège, Belgium, ²University of Liège, Liège, Belgium

Roya Sharifpour  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Fermin Aizpurua  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Ilenia Paparella  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Islay Campbell  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Elise Beckers  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Nasrin Mortazavi  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Ekaterina Koshmanova  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Christophe Phillips, Prof  
University of Liège
Liège, Belgium

Gilles Vandewalle  
Sleep and Chronobiology Lab, GIGA-Institute, CRC-In Vivo Imaging Unit, University of Liège
Liège, Belgium

Given the high levels of short wavelength blue light we are exposed to in modern life and the biological impact of light on sleep-wake regulation ( Münch 2017, Gooley 2011), it is important to fully understand the impact of light on brain function, especially in adolescents, as they may be more susceptible to the biological effects of light. Cortical excitability is a basic and yet fundamental aspect of brain function and cognition that depends on sleep-wake regulation (Ly 2016). Here, we assessed whether cortical excitability of healthy adolescents and young adults was affected by blue light exposure using electroencephalogram (EEG) recordings of transcranial magnetic stimulation (TMS).

Thirty participants, 16 adolescents (16.9±1.1y, 5 Females) and 14 young adults (24.0±3.6y, 6 Females) were included in the study. Participants followed a loose sleep-wake schedule for 5 days prior to the experiment (±1h) to avoid excessive sleep restriction. On the experiment day, participants arrived at the laboratory ~8h after wakeup time and were maintained in dim-light (< 10 lux) for 1h prior to the first TMS-EEG session. The stimulation target was set to the supplementary motor area on the dominant hemisphere. TMS-evoked responses (TEP) were recorded in 2 sessions under 2 different light conditions including a control orange light (30 lux, 24 melEDI lux) and an active blue light (30 lux, 312 melEDI lux). Sessions were separated by at least a 15-minute washout period in dim light (< 10 lux). The order of the sessions was randomized. Each session included around 250 trials and TEP were recorded using a 60-channel EEG amplifier. Data preprocessing was performed using MNE python package. Continues EEG data was filtered, visually inspected, re-referenced to the average of good channels and epoched. Independent components of the epochs were computed and components representing TMS artifacts were set to zero. Artifact free epochs were split to shorter epochs (-300 to 300 ms), re-referenced to the average of good channels and baseline corrected (-100 to -1.5ms ). Cortical excitability was then inferred from the amplitude and slope of the first EEG component (0–30 ms) of the mean TEP measured at the closest electrode to the stimulation. Statistical analyses consisted of Generalized Linear Mixed Models, with subject as random factor, light condition as repeated measures, and age group sex and BMI as covariates.

GLMM analysis also showed yielded a illuminance by age group interaction (p = 0.03) (Fig1). Post hoc comparisons indicated that amplitude was higher during the blue light session compared to the orange in young adults (p=0.007), while in adolescents the amplitude did not change significantly (p = 0.8). GLMM analysis of the TEP slope did not reveal any main effects (p > 0.05) neither any illuminance by age group interaction (p=0.1). However, post hoc comparisons revealed significantly higher slope during the blue session compared to the orange in young adults (p=0.03), and no significant change in adolescents (p=0.9).

These preliminary findings suggest that adolescents may not be more sensitive to the biological impact of blue light on sleep-wake regulation or that they are very sensitive to it and reached saturation under the orange light.


Funding: European Union (LIGHTCAP Project), FNRS, ULiège, FEDER, Fondation Léon Frédéric.

Non-invasive Magnetic/TMS ²

Early life, Adolescence, Aging ¹

Sleep and Wakefulness

Cognition

Electroencephaolography (EEG)

Transcranial Magnetic Stimulation (TMS)

Other - blue light