The Importance of Cognition in the Conceptualization of both Dementia and Severe Mental Illness in Older People

In the July/August 2004 issue of the American Journal of Geriatric Psychiatry, Dr. Barton Palmer’s introduction to the theme of Neuropsychology discussed the expanding role of neuropsychology in geriatric psychiatry. This issue’s theme is Cognition, which focuses less on the localization of cognitive impairment in the brain and more on the importance of cognition in understanding disease states. Cognitive impairment has long been understood as the hallmark of degenerative dementias such as Alzheimer disease, of course, but our understanding of the cognitive components of severe mental illness is still developing, as is our appreciation of the nature and strength of the linkage between cognition and the functional outcomes that are important to patients and their families. Psychiatric disorders, brain disorders that they are, are increasingly being conceptualized as having significant cognitive components. The empirical articles in the American Journal of Geriatric Psychiatry during 2005, for example, addressed cognition not only in Alzheimer disease, but also in stroke and anxiety and depression. The impact of cognition on function in both healthy elders and psychiatric populations also was highlighted. All of the severe mental illnesses appear to feature significant cognitive impairment along with psychiatric symptoms. Interestingly, these cognitive impairments are generally not a function of the other aspects of the illness, as striking as these features may be. Schizophrenia has increasingly been conceptualized as a cognitive disorder producing psychosis, rather than a psychotic disorder affecting cognition. The neuropsychological deficits of schizophrenia occur in multiple domains, including attention, working memory, learning, memory, processing speed, and executive functioning, and are relatively stable over time. The cognitive impairments seen in affective disorders, too, are increasingly being viewed as central to the illness, rather than mere epiphenomena. Bipolar disorder patients, even when in euthymic states, have cognitive deficits that are qualitatively and quantitatively similar to those seen in schizophrenia. Depression, too, has long been associated with cognitive dysfunction comparable to that seen in both bipolar disorder and schizophrenia. In one study of stable outpatients, schizophrenia and bipolar subjects did not differ on 9 of 10 neuropsychological tests administered; in another study of chronically institutionalized patients, there were no overall differences between patients with schizophrenia, unipolar depression, and bipolar disorder on an 11-test cognitive assessment, while 18/30 PANSS items differed between the groups. As is the case in bipolar disorder and schizophrenia, the cognitive impairments of depression are seen even in stable outpatients. Both unipolar depressed and bipolar patients show deficits in verbal learning and memory consistent with an encoding deficit. The public health significance of cognitive functioning in older people cannot be understated. Better recognition of Alzheimer disease in its earliest state, for example, would have profound social and financial effects. Cognitive impairment also is a leading cause of disability in severe mental illness, often even