title: The sudden infant death syndrome induced by "the fear paralysis reflex'?
abstract: The sudden infant death syndrome (SIDS) is the greatest single cause of death between one month and one year of age in industrial countries. Its etiology still remains a mystery despite extensive research during the past decades. The outstanding problem is to define the trigger mechanism leading to death. Most theories have dealt with bodily malfunctions, infections and toxic agents, and only minor attention has been paid to a possible psychical trigger mechanism. The hypothesis is advanced that the so-called 'fear paralysis reflex' (for other terms, see below), an atavistic reflex present in the entire animal kingdom, may be a major trigger mechanism for SIDS. The reflex is evoked by fear resulting from any threatening event which is perceived as a danger, and with which the organism is unable to cope, typically in a predator confrontation. Important threatening stimuli in animals, and which may be of particular importance in human infants, are restraint of movement, sudden and unfamiliar noises, separation from the mother and companions, and sudden exposure to an unfamiliar environment. The main response characteristics are an immediate motor 'paralysis' (prolonged and generalized immobility), unresponsiveness, and abrupt and profound bradycardia. The latter may proceed to asystole and fatal cardiac arrythmias. Any hypothesis attempting to explain the cause of SIDS must account for the unique age distribution of SIDS' victims with a peak age incidence at 2-4 months, its frequent occurrence in REM sleep, and the observation that most deaths are silent. Further, it must be consistent with previously established risk factors (genetic determination, opiate-addicted mothers and cigarette smoking). The fear paralysis hypothesis is in accordance with all these facts, and it suggests new and potentially hazardous triggering mechanisms which, one recognized, possibly can be avoided. As a central reflex, it does not leave any trace in the organism, which explains the negative postmortem findings. Suggestions for testing the hypothesis are given, and possible preventive measures are presented.
mesh_terms: D000367:Age Factors; D000818:Animals; D005075:Biological Evolution; D005239:Fear; D006339:Heart Rate; D006801:Humans; D007223:Infant; D051379:Mice; D012018:Reflex; D012119:Respiration; D012895:Sleep, REM / Q000502:physiology; D013398:Sudden Infant Death / Q000209:etiology*