Effects of repeated cortisol administration on brain potential correlates of episodic memory retrieval

Neuropsychological impairments in depressive illness may be secondary to hypercortisolaemia. Cortisol administration to healthy subjects impairs episodic memory, though how this is mediated is unknown.

To examine the effects of 1 week's administration of cortisol on the neural correlates of episodic memory in healthy subjects.

Fourteen healthy men were treated with oral cortisol (hydrocortisone 20 mg) or placebo twice daily for 1 week, in a double blind, crossover fashion. Event related potentials (ERPs) were recorded during a well-validated source memory task. Subjects listened to words spoken in a male or female voice. At test, old and new words were presented visually; subjects judged whether words were old or new, and if old, the gender of the voice at study.

Response times were significantly speeded by cortisol. A significant reduction in recognition accuracy with cortisol was found for the second study occasion. ERP recordings with placebo showed greater positivity over left parietal and right frontal scalp areas for ERPs to items given correct source judgements versus correctly rejected new items. In comparison, cortisol increased ERP voltage between 500 and 1400 ms post-stimulus and this effect interacted with item type and electrode site, being diffusely distributed for correct rejections but of a lesser magnitude frontally for old items accorded a correct source judgement.

Repeated cortisol administration leads to a qualitative change in the neural correlates of episodic memory retrieval in healthy subjects. This change may contribute to cognitive impairments seen in illnesses characterised by hypercortisolaemia.