Psychologists dispute whether there is a strong basis to support the concept of repressed memory. Many psychologists, however, believe children can learn to block memory as a survival mechanism. Other researchers argue publicity about child abuse has fostered a climate in which hidden abuse is believed to be the cause of many people's ill-defined symptoms of distress. Alternatively, there may be a biological explanation for repressed memory. The human brain produces natural opiates in response to trauma that block the formation of long-term memory, and this blocked memory may later be revived when stress prompts the body to produce adrenaline. The authors conclude the action of endogenous opiates and noradrenaline in the amygdala and the hippocampus may provide a biological framework for examining how memory is repressed and later retrieved, but they do not discount psychological effects on memory.