Washington, Oct 24 : Ever wondered why dark rooms are so scary and dim corners make your heart skip a beat? Now, a study has found evidence to show how darkness when combined with social stress increases anxiety.

Dr. Christian Grillon and his team at the National Institute of Mental Health conducted a study to see if stress increases unconditioned fear in humans.

To find this, they measured the startle reflex of healthy volunteers in either light or dark conditions, and after either a socially stressful situation of public speaking, or after a period of relaxation.

The startle response is a sensitive tool for measuring anxiety levels, and in this study, was measured when volunteers were presented with white noise stimuli via headphones. The authors found that the startle response was boosted when the volunteers were in complete darkness, and this effect was more pronounced after the stressor.

“Because stress has been linked to the precipitation of emotional disturbances, sometimes to a pathological level, it is important to understand how stress affects our brain and behaviour.” Dr. Grillon, lead author on the project, said.

“We report that a mild acute stressor increases subsequent experimental anxiety in healthy subjects. The demonstration of stress-induced anxiety in the laboratory is important because it provides how stress alters nervous system function,’ Dr Grillon said.

John H. Krystal, M.D., Editor of Biological Psychiatry and affiliated with both Yale University School of Medicine and the VA Connecticut Healthcare System, said that the research an help explain how threatening contexts and stressful social interactions contribute to anxiety disorders.

“The authors show that social stress and darkness interact to increase the startle response. The refinement of this research method may help us to understand how threatening contexts and stressful social interactions interact at a mechanistic level to contribute to anxiety disorders," Krystal said.

The study will appear in the November 15th issue of Biological Psychiatry (ANI)