An anxious witness takes the stand and then can't remember crucial details of her story. Faked or forgotten? A new study that teases apart the effects of a stress hormone on memory might exonerate the witness. The findings, which appear in the April issue of Nature Neuroscience, suggest that cross-examinations or other stressful situations may impair our ability to recall memories.
The brain deals with memory in three stages. It first acquires new information, which it then consolidates and stores. Finally, when we need a fact or figure, the brain retrieves it. Some studies have shown that cortisol, a hormone released by the adrenal glands in reaction to stress, can impair memory, possibly by disrupting the consolidation. But based on their earlier work with rats, researchers led by Dominique de Quervain, a physician at the University of Zürich in Switzerland, suspected cortisol might instead hamper retrieval of memories.
The team asked 36 people to memorize 60 verbs. The subjects were asked to recall as many words as they could immediately after the test and again 24 hours later. A tablet of cortisone (which the body rapidly converts to cortisol) given to the subjects an hour before or just after they first viewed the word list did not change their performance--evidence that the hormone had not affected memory acquisition or storage. But when subjects were given cortisone an hour before taking the second test, their scores fell from an average of 17 words remembered to 11; the stress hormone had reduced memory retrieval by a whopping 35%.
The work is "really quite surprising," says Carol Barnes, a neuroscientist at the University of Arizona, Tucson. "You usually think of the newly formed memories as more vulnerable. But in this study the presumably robust, consolidated memories are the ones in jeopardy. And the team nicely controlled for this." De Quervain says he now wants to study the memory damage that's triggered by long-term exposure to cortisol from conditions such as chronic depression.