Masayuki Kondo

Dorsolateral prefrontal cortical oxygenation during REM sleep in humans

Previous neuroimaging studies that examined cerebral blood flow during rapid eye movement (REM) sleep have reported inconsistent findings regarding the activity of the dorsolateral prefrontal cortex (DLPFC). Although most previous positron emission tomography (PET) studies failed to detect DLPFC activation during REM sleep, several studies have observed DLPFC activation, possibly reflecting transient prefrontal activities related to REM. More recently, an event-related functional magnetic resonance imaging (fMRI) study observed REM-locked activation of the DLPFC during REM sleep. The present study investigated hemodynamic changes of the DLPFC throughout the REM sleep period in 25 subjects using near-infrared spectroscopy. Continuous monitoring of changes in the hemoglobin (Hb) concentration and tissue oxygenation index (TOI, proportion of oxygenated-Hb to total-Hb) in the bilateral DLPFC was conducted every 0.5s, simultaneously with polysomnographic recordings. Eight of the 25 subjects showed REM sleep, and all indicated a clear increase in both the oxygenated-Hb concentration and TOI from baseline at the occurrence of first REM, relative to prior stage 2 sleep. The results indicate that the appearance of the first REM that occurred just after onset of the REM sleep closely coincides with the activation of the DLPFC, which could play a role in cognitive activities during REM sleep in humans.

Salivary Secretion under the Influence of Bright/Dim Light Exposure in the Morning and Evening in Humans

Recent studies show that bright and dim light intensities during the daytime have important regulatory functions. Our present study was performed to evaluate the effect of exposure to different light intensities during the morning and evening on salivary secretion and its sodium concentration. The study involved 6 healthy, female volunteers who were exposed to dim light (100 lx) from 7:00 to 17:00 and to bright light (3000 lx) from 17:00 to 23:00 one day, and to bright light (3000 lx) from 7:00 to 17:00 and dim light (100 lx) from 17:00 to 23:00 on the next day. We collected salivary samples every 10 minutes during 2 hours in the morning and in the evening by means of a Lashley cup. Saliva secretion was stimulated by sweet candy. The amount of saliva secreted was significantly greater in the morning under bright light exposure, while it was significantly greater in the evening under dim light exposure. We discuss these findings in terms of changes in activity of the parasympathetic nervous system (PNS) and sympathetic (SNS) nervous system produced by exposure to different light intensities at different times of the day.

Effect of Dim and Bright Light Exposure on Some Immunological Parameters Measured under Thermal Neutral Conditions

This study assesses the effects of ambient light conditions, under a thermoneutral environment, on selected immunological parameters of 7 healthy young women (aged 19 to 22 yrs). Subjects entered the bioclimatic chamber at 11∶00 h, controlled at 26°C and 60% relative humidity, a “neutral climate”. They lead a well‐regulated life in the climatic chamber (pre‐condition) while exposed to dim (200 lux) or, on the next day, bright (5000 lux) light between 06∶00 to 12∶00 h. Just before the end of each period of light exposure, a blood sample was taken for later immunological assay of white blood cell count (WBC), phagocytosis, interferon‐γ (IFN‐γ), interleukin‐4 (IL‐4), CD69 T cells (CD69), CD4+CD25+ T cells (CD4+CD25+), and transforming growth factor‐β 1 (TGF‐β1). The results, when compared with the pre‐condition, were as follows: 1) CD69 and IFN‐γ increased during normal conditions without thermal stress under dim light; 2) WBC increased and IL‐4 decreased under bright light; 3) as shown by the highly significant decrease of TGF‐β1, the immune system was activated under bright light; 4) phagocytosis tended to increase under bright light exposure; 5) CD69 and IFN‐γ were significantly higher, and CD4+CD25+ tended to decrease under bright light; 6) phagocytosis tended to be lower and TGF‐β1 significantly higher under dim light, indicating a decline of immune system function. Taken together, this preliminary single time‐point sampling study infers that some parameters are activated (CD69) while others are attenuated (phagocytosis, TGF‐β1) according to the environmental light intensity, dim vs. bright, in women adhering to a standardized routine in the absence of thermal stress. These findings are discussed in terms of inhibition of the sympathetic and excitation of the parasympathetic nervous system under the influence of life‐style regularity and daytime bright light exposure.