Stress hormones impair memory

High serum concentrations of cortisol may be responsible for stress induced memory loss, a team of researchers from Zurich has found. They compared the effects of oral cortisol and placebo in a randomised trial and found that the cortisol group did worse in tests of recall than controls. The research was prompted by animal research suggesting that learning was enhanced in animals given glucocorticoids.

In this study, the 46 subjects were randomised to take either 25 mg cortisone (which produced circulating cortisol concentrations equivalent to natural concentrations of cortisol at times of stress) or a placebo. They were all asked to memorise 60 nouns, each of which were presented on a computer screen for four seconds. Both groups were then tested for free recall (write down all the words you remember) and recognition (how many of the following words were on the list). The subjects were also tested for delayed recall, 24 hours after the initial presentation.

Subjects who were given 25 mg cortisol immediately before their recall test showed a significant deterioration in performance compared with those who took a placebo. Cortisone administration at other stages of the experiment showed no significant difference between the two groups. This suggests, say researchers, that physiological response to stress does not impair the "learning" aspects of memory but only the free recall of information. There was no significant difference between the treated and untreated group in their ability to recognise words presented.

Cortisol is one of the hormones produced by the adrenal cortex in response to stress. Previous research has suggested that exogenous cortisol impairs human overall memory performance, and long term hypercortisolaemic states such as depression, Cushing's syndrome, and old age are known to have strong associations with memory impairment.

"Elevated glucocorticoid levels may induce impairments in such stressful conditions as job interviews, combat, courtroom testimony and examinations," the authors conclude (Nature Neuro-science 2000;3:313-4 (April.)).