Neurobiological relationships between ambient lighting and the startle response to acoustic stress in humans.

A study was conducted to determine differences between psychophysiological responses to acoustic stress under different ambient lighting conditions. Typical cool-white indoor lighting was compared to full-spectrum lighting under dim and bright illumination levels. Full-spectrum lighting exhibits spectral characteristics that approximate those found in natural sunlight. The startle response was measured during three preliminary experiments using normal subjects. In the first experiment, one subject was evaluated. Electromyography (EMG) was used to measure eyeblink startle at the obicularis oculi muscle; heart rate (HR) was measured at the wrist; and galvanic skin conductance (GSC) was measured at the left index finger. There was a significant increase in galvanic skin conductance (GSC) and a decrease in heart rate. In the second experiment, GSC was used to measure the startle response under cool-white fluorescent lighting versus full-spectrum fluorescent lighting (n = 5 subjects) under both bright and dim lighting conditions. Higher arousal was detected measuring GSC under the cool-white lighting condition, and under the dim lighting condition using both types of lighting. In the third experiment, ten subjects were assessed for GSC startle response using both lighting types set at the dim brightness level. There was a strong trend indicating a higher GSC arousal under the dim cool-white lighting condition. Other studies support that a GABAergic inhibitory circuit is inhibited by darkness and that the spectral characteristics of cool-white lighting are more stressful to humans than full-spectrum lighting. These preliminary findings regarding stress and ambient lighting may be especially important in the neural development of children, and in those clinical populations that are particularly sensitive to environmental stress.