No evidence in favor of a more deleterious impact of a major depressive episode on verbal memory in older patients with antidepressant response

Background: Older patients may be more vulnerable to the deleterious effect of depressive episodes on delayed narrative memory, a cognitive task which reflects hippocampal activity. We aimed to disentangle which factors could explain such increased vulnerability in the elderly, including the poorer response to treatment, a longer lifetime exposure to past depressive episodes, and lower baseline memory skills. Methods: From an initial sample of 8,229 depressed outpatients, we focused on the 2,424 treatment responders, and compared older (65 years old and over, N = 233) to younger (N= 2,191) ones. These patients were included through general practitioners' assessment and tested for the Wechsler delayed paragraph recall index, a valid and sensitive test assessing verbal declarative memory (and a marker of the hippocampal function), at baseline and after six weeks of treatment. Results: As expected, older patients after response to antidepressants showed decreased narrative memory abilities compared to younger ones. As baseline memory performance and residual depressive symptoms were also found in excess in this sample, they could act as confounders. Indeed, after controlling for these two factors, the role of age in memory performance after treatment response was ruled out. Conclusions: The potential "toxicity" of a depressive episode to cognitive functions related to the hippocampus may not be more critical in older patients compared to younger ones. Limiting remaining depressive symptoms in older depressed patients might be a way to counteract the observed worsening of memory functions in depressed patients.