Daytime Acute Non-Visual Alerting Response in Brain Activity Occurs as a Result of Short- and Long-Wavelengths of Light

What is it about?

The results of this study implicate that human organisms are prone to stimulation leading to the prevention of the onset of sleepiness, which is necessary to be disposed to execute daily tasks requiring a high level of energy. In contrast to studies conducted so far proving the dominant role of blue light in the alerting non-visual response, we have shown that long-wavelength light induced a stronger and more spread over the scalp response of the bioelectrical activity during the daytime, which might suggest that a pathway other than the circadian system may affect light-induced daily alertness.

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Why is it important?

Surprisingly, the response was more spread over the scalp during exposure to red light than to blue light. According to our study, the response to long-wavelength stimulus that inhibits sleepiness, thereby inducing alertness, also takes place at the bright part of the twenty-four hour day when humans are naturally predisposed to be exposed to a high level of sunlight: between 12 and 4 PM. The absorption spectrum of the non-visual system seems to have different characteristics than was previously suspected: it is not dominated by the short-wavelengths, but involves long-wavelengths. Since we observed the predominance of the red-light alerting effect over the blue-light in this experiment, we conclude that more than one mechanism, beyond the melatonin pathway, must be involved.

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