The featured image of this post was complied from a post from allthingslighting. The blue LED light from many commercially available strips is not the cone blue light we typically think of but of melanopsin of ipRGC (Intrinsically photosensitive retinal ganglion cells). It should be noted that the photopigment, melanopsin, is in the cells that the photoreceptor rods and cones form synapses with via bipolar cells.
With the featured image of overlapping absorbances of the opsins we are ready to review some studies on 470 nm blue light.
Green vs violet vs Blue [1]
This study used fMRI to specifically assess early effects of light over the entire brain while participants were performing an auditory working memory task. The idea was to use medium duration pulses long enough to detect via MRI but not so long as to result in lasting brain changes. They used alternating 50 sec monochromatic LED light
- violet (430 nm), S cone
- blue (473 nm), melanopsin expressing RGC
- green (527 nm) M cone
Experimental Protocol.
The participants were chosen such they did not have altered circadian cycles due to night shift work, excessive caffeine consumption, and such as that.
Candewalle and coauthors used an easier version of the n-back test. Wikipedia authors give this example of a 3-back test when the test subject is supposed to indicate when the constanant immediately read is the same as that read three constanants previously.
T L H C H O C Q L C K L H C Q T R R K C H R
- nine French monosyllabic consonants
- 500 ms long
- inter-stimulus-interval was 2500 ms.
- identical to the consonant presented 2 stimuli earlier, by pressing a button
- ∼30% positive answers.
- 14 consonants each illumination period, 35s,
- 2 to 5 consonants were presented in half of the darkness periods, for a total of 5 to 12.5s.
- Series could therefore be 33 consonant long if a darkness period with the task was placed between 2 consecutive illumination periods where the task was performed
- Series were presented only once and were randomly assigned to one of the scanning sessions.
- Rest periods could last up to 44 s if a rest period in darkness was placed between two consecutive illumination rest periods.
Note that only statistically different brain regions between blue and violet illuminated subjects are shown. The brain stem region recruited by blue light was tentatively assigned to the locus ceruleus.
Amber vs Blue [2]
The blue LED light had a narrow bandwidth [peaking at λ = 469 nm, at 214 Lux at eye level, and panel irradiance (mW/cm2) = 1.23]. The amber source was a single LED [peaking at λ = 578 nm, at 188 Lux at eye level, and total irradiance (mW/cm2) = 0.35]. In commercial strips the illusion of amber is produced with RGB combinations. Table 2 of this report stressed that 578 nm light mainly activated L- and M-cones with little activation of S-cones, rods, and “melanoptic” ipRGC. 469nm blue light activated all photoreceptors with L-opsin being a little over one fifth that of melanopsin.
protocol
- 7:45 a.m. check in, demographic data collection
- 8:30 a.m. participants finished the first PANAS. and other cogntive assessments
- 9:45 a.m., “blue light washout” period in an otherwise darkened room, with only two amber light devices placed on the table in front of them for 30 min. This eliminated interference blue in ambient light.
- 10:15 a.m., participants were randomized to receive either 30 min of blue (n = 17) or amber (n = 12) light exposure. Two computerized practice tasks (a working memory and a multi-source interference task) were used to prepare them for their time in the scanner.
- 10:50 a.m., participants completed the second PANAS.
- 11:00 a.m., participants were escorted to the MRI scanner
- 11:15 a.m. resting state scan was the first functional scan followed by longer versions of the working memory and multi-source interference tasks.
Figure 1, the PANAS test
Alkozei and coauthors used a PANAS positive and negative affect schedule to assess the emotional status of the participants. Both colors of light decreased the intensity of negative and positive emotions. Blue light seemed to moderate the intensity of negative emotions more. The authors speculated that the participants might have been apprehensive about being in a clinical trial and less emotional one way or another after actually experiencing the light exposure.
Figure 2 Connectivity via MRI
The left and right amygdala were defined as seed regions of interest (ROI). Confounding factors were removed. The residual blood oxygen level dependent BOLD time-series from the bilateral amygdala seed ROIs were averaged to generate a mean time-series. This form of MRI can detect utilization of oxygen carried by hemoglobin in he blood by active regions of the participants’ brains. Bivariate correlation maps of other areas of the brain were compared. Corrections were made for age and sex.
As an aside brainbasedlearning has an interesting post on this cortico-limbic system as it relates to teenagers learning. Most notably the Dorsolateral Prefrontal Cortex – is associated with motivation and the Amygdala is associated with emotional stress and learning.
Figure 3 Granger causality
Granger causality investigates the ability of one time series to predict the other, which was estimated by quantifying the inter-relationships between their oscillatory mechanisms as a function of frequency (f ) of oscillations. Feed-forward [right amygdala (R. AMG) to left DLPFC (L. DLPFC)] and feed-backward (L. DLPFC to R. AMG) connections were significant for the blue light group but not the amber light group at 0.08 Hz.
PANAS score and amygdala and DLPFC connectivity
Alkoxzei and coauthors also correlated the self assessment mood scores with increased functional connectivity between the amygdala and DLPFC. This connectivity was monotonically associated with reduced PANAS-N scores for the blue light group (ρ = −0.55, p = 0.03) but not the amber light group (ρ = −0.18, p = 0.55). Here ρ is Pearson’s correlation coefficient R.
Amber vs Blue cont. [3]
The Killgore group published a follow up study a year later. This time they were using the left DLPFC as the reference area. The subjects took a psychomotor vigilance test. Blue, but not amber, light resulted in increased connectivity with the right amydala and 30 other regions including many in the hippocampus and temporo-occipital cortex.
Conclusions
The Candewalle study. The Alkozei publication had a nice discussion of depression as it relates to amygdala and DLPFC connectivity and seasonal affective disorder. The possibility that amber light has a calming affect was left open. The 2022 Killgore speaks to a greater role of blue slight melanopsin in our brain function. Do other wavelengths of light mitigate the effect of
References
- Vandewalle G, Schmidt C, Albouy G, Sterpenich V, Darsaud A, Rauchs G, Berken PY, Balteau E, Degueldre C, Luxen A, Maquet P, Dijk DJ. Brain responses to violet, blue, and green monochromatic light exposures in humans: prominent role of blue light and the brainstem. PLoS One. 2007 Nov 28;2(11):e1247 PMC free article
- Alkozei A, Dailey NS, Bajaj S, Vanuk JR, Raikes AC, Killgore WDS. Exposure to Blue Wavelength Light Is Associated With Increases in Bidirectional Amygdala-DLPFC Connectivity at Rest. Front Neurol. 2021 Mar 26;12:625443. PMC free article
- Killgore WDS, Alkozei A, Vanuk JR, Reign D, Grandner MA, Dailey NS. Blue light exposure increases functional connectivity between dorsolateral prefrontal cortex and multiple cortical regions. Neuroreport. 2022 Mar 23;33(5):236-241 PMC free article
