Selective amnesic effects of oxytocin on human memory.
The neuropeptide oxytocin is essential for mammalian parturition and lactation. Recent animal studies suggest that oxytocin is also implicated in the central nervous control of behavior including learning and memory. There has been little investigation, however, of the impact of oxytocin on human memory. The purpose of this study was to investigate the effect of a single dose of intranasal oxytocin on implicit and explicit memory in humans. In a placebo-controlled, double-blind study, 38 healthy men were randomly assigned to receive intranasal oxytocin (24 IU) or placebo 50 min before the study phase (incidental learning). Memory was measured using three different memory tests: an implicit perceptual test (word stem completion), an implicit conceptual test (category-cued semantic association), and an explicit test (cued recall). Due to the reproductive-biological role of oxytocin and the impact of adequate environmental conditions for the stimulation of behavioral effects of oxytocin known from animal research, we used semantic word stimuli with reproduction-related vs. neutral meaning. Oxytocin significantly impaired recall performance as compared with placebo treatment irrespective of the meaning of words in the cued recall test. In the implicit conceptual test, characterized by a deepened information processing, compared with placebo, oxytocin significantly impaired only the overall generation of associated target words with reproduction relevant meaning, whereas no significant difference between oxytocin and placebo was obtained for neutral words. These findings concur with data from animal research suggesting that central oxytocin selectively influences memory performance depending on the kind of memory test used and, more importantly, the psychobiological relevance of stimuli.