The role of shock predictability during aversive conditioning in producing psychosomatic digitalis toxicity

Guinea pigs were subjected to Pavlovian fear conditioning (signaled shock) and then infused with a fast acting digitalis preparation on a day when all experimental stimuli except shock were delivered. A significant shortening in latency to the onset of life-threatening digitalis toxicity was found when comparisons were made to control pigs that had never been shocked. This effect was not found in other guinea pigs infused with ouabain after exposure to sessions of unsignaled shock. These experiments indicate that psychological factors, when divorced from physical factors, may produce lethal digitalis toxicity in an organism that would otherwise be asymptomatic. The data from these experiments suggest that the intense arousal associated with a signal that had previously been paired with shock is sufficient to precipitate cardiac arrhythmias in an animal with a predisposition to cardiac automaticity such as is produced by digitalis. Conversely, the less intense arousal associated with unsignaled shock is inadequate to produce this effect. This interpretation indicates that the state of an animal's health will affect its psychosomatic response to signaled or unsignaled shock.