Crystalline lens transmittance spectra and pupil sizes as factors affecting light-induced melatonin suppression in children and adults.

PURPOSE: To investigate the contributions of ocular crystalline lens transmittance spectra and pupil size on age-related differences in the magnitude of light-induced melatonin suppression at night. The first aim was to demonstrate that spectral lens transmittance in children can be measured in vivo with a Purkinje image-based system. The second aim was to test the hypothesis that the magnitude of melatonin suppression in children is enhanced by larger pupils and higher lens transmittance of short wavelengths. METHODS: Fourteen healthy children and 14 healthy adults participated in this study. The experiment was conducted for two nights in our laboratory. On the first night, the participants spent time under dim light conditions (<10 lux) until one hour after their habitual bedtime (BT+1.0). On the second night, the participants spent time under dim light conditions until 30 min before their habitual bedtime (BT-0.5). They were then exposed to LED light for 90 min up to BT+1.0. Individual pupil sizes were measured between BT and BT+1.0 for both conditions. Lens transmittance spectra were measured in vivo using the Purkinje image-based system during the daytime. Non-visual photoreception was calculated from lens transmittance and pupil size. This was taken as an index of the influence of age-related ocular changes on the non-visual photopigment melanopsin. RESULTS: Measured lens transmittance in children was found to be higher than for adults, especially in the short wavelength region (p < 0.001). Pupil size in children was significantly larger than that of adults under both dim (p = 0.003) and light (p < 0.001) conditions. Children's non-visual photoreception was 1.48 times greater than that of adults, which was very similar to the finding that melatonin suppression was 1.52 times greater in children (n = 9) than adults (n = 9). CONCLUSIONS: Our Purkinje image-based system can measure children's lens transmittance spectra in vivo. Lens transmittance and pupil size may contribute to differences in melatonin suppression between primary school children and middle-aged adults.

A study of EEG mu neurofeedback during action observation.

The mirror system is a brain network that gets activated during action performance and observation. Brain mu waves have been used as a mirror system activity index; however, mu rhythm is prone to contamination by occipital alpha wave activity, thus raising a concern regarding its reliability as an index of the mirror system activity. In this study, we investigated whether mu suppression can be used as an index of neurofeedback training, which influences mirror system activities. Participants observed videos of hand movement under three different conditions: central mu feedback (muFB), occipital alpha feedback (aFB), and simple observation without any feedback (OBS). Results showed that at the 4-5 min mark, mu wave was most significantly suppressed in the central site at muFB. We thus demonstrated the possibility of increasing mu wave suppression in feedback training using a specific stimulus such as motion observation.