Depression does not aggravate the episodic memory deficits associated with Alzheimer's disease

In a population-based study of persons between 75 and 96 years of age, normal old adults (n = 296), patients with Alzheimer's disease (AD; n = 45), and patients with concomitant AD and depression (AD-D; n = 9) were compared on free recall and recognition of slowly and rapidly presented words and digit span. With the exception of forward digit span, the normal old group outperformed the 2 AD groups across all tasks. In free recall, only the normal old group performed better as task pacing decreased; however, all groups benefited from more study time in recognition. This suggests that both AD and AD-D patients have deficits in the ability to use more study time for remembering. Of most importance, the 2 AD groups were indistinguishable for all task variables. This lack of comorbidity effects is discussed relative to the view that depression, much like many other individual-difference variables that affect memory performance in normal aging, may be overshadowed by the influence of the neurodegenerative process in AD.