title: The human fear-circuitry and fear-induced fainting in healthy individuals--the paleolithic-threat hypothesis.
abstract: The Paleolithic-Threat hypothesis reviewed here posits that habitual efferent fainting can be traced back to fear-induced allelic polymorphisms that were selected into some genomes of anatomically, mitochondrially, and neurally modern humans (Homo sapiens sapiens) in the Mid-Paleolithic because of the survival advantage they conferred during periods of inescapable threat. We posit that during Mid-Paleolithic warfare an encounter with "a stranger holding a sharp object" was consistently associated with threat to life. A heritable hardwired or firm-wired (prepotentiated) predisposition to abruptly increase vagal tone and collapse flaccidly rather than freeze or attempt to flee or fight in response to an approaching sharp object, a minor injury, or the sight of blood, may have evolved as an alternative stress-induced fear-circuitry response. Such a stable (balanced) polymorphism for the hemodynamically "paradoxical" flaccid-immobility in response to these stimuli may have increased some non-combatants' chances of survival. This is consistent with the unusual age and sex pattern of fear-induced fainting. The Paleolithic-Threat hypothesis also predicts a link to various hypo-androgenic states (e. g. low dehydroxy-epiandrosterone-sulfate. We offer five predictions testable via epidemiological, clinical, and ethological/ primatological methods. The Paleolithic-Threat hypothesis has implications for research in the aftermath of man-made disasters, such as terrorism against civilians, a traumatic event in which this hypothesis predicts epidemics of fear-induced fainting.
authors.affiliation: National Center for Posttraumatic Stress Disorder, Dept. of Veterans Affairs, Pacific Islands Health Care System, Spark M. Matsunaga Medical Center, Honolulu, HI 96813-2830, USA. H.Bracha@med.va.gov
authors.forename: H Stefan
authors.initials: HS
authors.lastname: Bracha
authors.forename: Adam S
authors.initials: AS
authors.lastname: Bracha
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Williams
authors.forename: Tyler C
authors.initials: TC
authors.lastname: Ralston
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Matsukawa
mesh_terms: D000328:Adult; D017668:Age of Onset; D000375:Aging / Q000502:physiology; D000728:Androgens / Q000502:physiology; D005075:Biological Evolution; D001794:Blood Pressure / Q000502:physiology; D005239:Fear / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011965:Receptors, Glucocorticoid / Q000502:physiology; D018161:Receptors, Mineralocorticoid / Q000502:physiology; D013575:Syncope / Q000235:genetics / Q000503:physiopathology*; D014857:Warfare
chemical_list: D000728:Androgens; D011965:Receptors, Glucocorticoid; D018161:Receptors, Mineralocorticoid