A direct light pathway to the brain and its immunological effect

Visible light has been suggested to modulate the immune response through an eye-brain mechanism. On the other hand, penetration of light through the cranial bone has been demonstrated in non-mammalian vertebrates. A red light diode was used to illuminate the forehead while the eyes were shielded in 8 healthy male human subjects. Natural killer (NK) cell activity (NK activity) and number of peripheral NK cells (CD57-CD16+) were examined. The relationship between changes in these immunological parameters and changes in brain alpha waves was also studied. After a 15-minute session of red light diode exposure, a tendency was observed toward increased NK activity, and a significant increase in the level of CD57-CD16+. In addition, among these parameters, a significant correlation was observed between the change in level of CD57-CD16+ and change in alpha wave effective amplitude measured during the first 5-minutes in the bilateral frontal regions. However, this correlation was not significant in the occipital regions. These results indicated that frontal exposure to red light from a diode, which might directly penetrate the human frontal bone, appeared to induce changes in alpha amplitude predominantly in the frontal hemisphere. This was postulated to lead to release of neurotransmitters, thereby accounting for the observed changes in peripheral NK cells.