A study of the neural correlates of episodic memory and HPA axis status in drug-free depressed patients and healthy controls

Altered laterality of cortical activity, neuropsychological impairment and hypercortisolaemia have been shown in depression. The neural correlates of episodic memory in healthy subjects demonstrate hemispheric laterality but it is not known whether this is affected by depression and/or hypercortisolaemia. Twenty-seven drug-free depressed patients and 29 matched healthy controls were studied. Event-related potentials (ERPs) were recorded during an episodic memory test. During the study phase, subjects heard words spoken in either a male or female voice. Old and new words were presented visually during a test phase, when subjects were requested to identify words as old or new and recollect the gender of the voice for old words. Cortisol levels were measured in saliva and plasma samples. The results showed a trend for elevated salivary cortisol concentration in depressed patients. Reaction times were significantly longer in patients; however, there was no difference in memory accuracy performance between the two groups. Recollection performance was found to be negatively correlated with age, with a similar trend for cortisol concentrations. ERP activity not specifically related to episodic memory retrieval recorded 200-500ms post-stimulus from controls showed a marked laterality, with higher voltages over the right hemisphere; however, was not seen in patients. There was significant correlation between cortisol and the laterality of the neural activity specifically related to episodic memory retrieval recorded 500-1400ms post-stimulus in both depressed and healthy groups. These unique findings demonstrate that while the laterality of the neural correlates of episodic memory is sensitive to cortisol, it is not altered by the non-specific laterality effects seen in depression.