Psychologists Nathan DeWall of the University of Kentucky and Roy Baumeister of Florida State University say that the reason people are paralysed with fear when faced with death is because they cope by thinking about happier thoughts.
This they say, is based on an emerging idea called "terror management theory" that hypothesises that the brain is hard-wired to keep us from being paralysed by fear.
According to this theory the brain allows us to think about dying, even to change the way we live our lives, but not cower in the corner, paralysed by fear. The automatic, unconscious part of our brain in effect protects the conscious mind.
To support their theory, the researchers carried out three experiments in the laboratory.
They asked volunteers to think about what happens physically as they die and to imagine what it is like to be dead.
Once the volunteers were preoccupied with thoughts of death and dying, they completed a series of word tests, which have been designed to tap into unconscious emotions. For example, volunteers might be asked to complete the word stem "jo_" to make a word.
They could make a neutral word like job or jog, or they might instead opt for the emotional word joy.
The idea is that the results represent the unconscious mind at work.
The researchers found that the volunteers who were preoccupied with thoughts of death were emotionally not at all morose.
In fact, they were much more likely than control subjects to summon up positive emotional associations rather than neutral or negative ones.
This, the psychologists suggest is because the brain is involuntarily searching out and activating pleasant, positive information from the memory banks in order to help the brain cope with an incomprehensible threat.
The results are reported in the November issue of Psychological Science, a journal of the Association for Psychological Science.