To our knowledge, this is the first study to show that elderly depressed patients with suicide attempts and severe suicidal ideation demonstrate poorer cognitive and, particularly, executive performance compared to nonsuicidal depressed elderly. These differences are not explained by the burden of physical illness, severity of depression, presence of clinical dementia or other cognitive disorders, effects of substance use, or psychotropic medication exposure. In agreement with the findings of Keilp and colleagues in younger adults,14
the deficits did not appear to reflect brain injury from suicide attempts.
Although the study was conducted at a tertiary care center, the inclusion of patients with comorbid substance use and cognitive disorders adds to the gener-alizability and clinical relevance of our findings. Other strengths of our study include comprehensive medical and psychiatric clinical characterization, and a detailed assessment of suicidal attempts and ideation.
The case-control design represents the main limitation of our study and precludes strong causal inferences. For example, an alternative hypothesis regarding the relationship between cognitive function and suicide has been articulated in the schizophrenia literature40
and states that persons lacking the ability to plan are less capable of a suicide attempt. Although this does not seem to be the case in patients with depression,14,15,18
only a prospective study can conclusively rule out such a possibility. It is also conceivable that people who commit suicide (and thus cannot be assessed neuropsychologically) plan their attempts better. Additionally, while the suicidal and nonsuicidal groups were equated on factors known to affect cognitive ability, the nonsuicidal comparison patients may have differed from our suicidal patients on other unknown but important characteristics. For example, since all of the suicidal patients and only half of our nonsuicidal patients were assessed as inpatients, the unfamiliar environment and other factors associated with hospitalization may have influenced cognitive performance. Ceiling effects on the DRS and its sub-scales represent yet another limitation: designed for assessing dementia, this test may be relatively easy and therefore not sensitive for most nondemented depressed patients. Thus, although we observed marked differences in executive functioning on the EXIT25 and the Memory and Attention subscales of the DRS, differences in other cognitive domains may be underestimated. Also, we cannot say how specific the executive function deficits are in the absence of a test of premor-bid intelligence or sensitive comparative measures such as a verbal learning task.
Our finding of poorer executive performance in suicidal depressed participants is similar to the observations of King and coauthors,18
who found that suicide attempters aged 50 and older performed more poorly on the Trail Making Test—Part B with increasing age than depressed comparison patients. Conceivably, such deficits may predispose a depressed patient facing physical illness8,41
or interpersonal loss5,6
toward a suicidal crisis through impaired problem-solving and perspective-taking. Indeed, persons with poorer executive functioning demonstrate difficulties in coping with physical illness as shown by noncompliance with human immunodeficiency virus treatment,36
diminished capacity to give informed consent,37
and trouble learning to use inhalers.39
Similar findings have been reported for self-care35
and financial competency,38
which is also noteworthy because financial stressors have been implicated in late-life suicide,42,43
and our patients often name them as a precipitant of their suicidal crisis. These factors may be particularly suicido-genic when they are not mitigated by social support.44
Although these and previous14,18
findings seem to support the role of executive dysfunction, it is still unclear how exactly they lead to suicidal ideation and attempts. Future studies will need to examine this association by focusing on specific cognitive areas that are important for real-life functioning, including problem-solving, decision-making, forward planning, and affective processing. Finally, although it seems plausible that these cognitive abilities moderate the impact of life and health stresses on suicidal behavior in the elderly, longitudinal studies are needed45
to explore this relationship.