Cognition represents the most important function of the human brain and the essence of the mind. Cognitive functions such as memory, learning, comprehension, processing speed, attention, planning, and problem-solving are the best indicators of the status of brain health.
Many psychiatric brain disorders are associated with cognitive impairments. Decades of extensive research have documented that the most severe cognitive deficits occur in schizophrenia. No wonder Emil Kraepelin coined the term “dementia praecox,” which means premature dementia (in youth)1 for this neuropsychiatric brain disorder. This condition was later renamed schizophrenia by Eugen Bleuler,2 who regarded it primarily as a thought disorder, with splitting of associations (not split personality, as misinterpreted by many in the public). Interestingly, a century ago both of those early masters of psychiatry de-emphasized psychotic symptoms (delusions and hallucinations), regarding them as “supplemental symptoms.”3 Yet for the next 100 years, clinicians overemphasized psychotic symptoms in schizophrenia and overlooked the more disabling cognitive impairment and negative symptoms, referred to as Bleuler’s 4 A’s—Associations disruption, Ambivalence, Affect pathology, and Avolition—symptoms that persist even after the psychotic symptoms are successfully treated.3
Most contemporary researchers regard cognitive impairment as the “core” feature of schizophrenia.4 The justification of this view is that cognitive deficits are detected in childhood and early adolescence (by age 13),5 long before the appearance of psychotic symptoms, and many studies have confirmed that cognitive deficits are the primary cause of functional disability and unemployment of patients with schizophrenia. Cognitive dysfunction is also found in milder forms in the parents and siblings of patients with schizophrenia,6 and is thus considered an “endophenotype” of the illness.
Because of its centrality, cognition has emerged as a major focus of schizophrenia research over the past 20 years. Multiple stakeholders (academic investigators, the National Institute of Mental Health, and the FDA) have collaborated to develop a standard measurement for cognition in schizophrenia. The project culminated in what was labeled MATRICS (Measurement and Treatment Research to Improve Cognition in Schizophrenia).7 The MATRICS settled on a battery of 7 major cognitive functions that are often impaired in individuals with schizophrenia (Table 18). Most contemporary researchers have adopted MATRICS in their studies, which facilitates replication to confirm research findings.
Measuring cognition in patients with schizophrenia is extremely important, as critical as measuring fasting glucose in patients with diabetes or blood pressure in patients with hypertension. Measuring the extent of impairment or nonimpairment across various cognitive tests can help with vocational rehabilitation, to place a patient in a job consistent with their level of cognitive functioning. In addition, once medications are developed and approved for cognitive impairments in schizophrenia, measuring cognition will be necessary to gauge the degree of improvement.
Currently, few psychiatric practitioners measure cognition in their patients. This is perplexing because cognitive measurement is important for confirming the diagnosis of schizophrenia in first-episode psychosis, or distinguishing it from other psychotic disorders (such as drug-induced psychosis, brief reactive psychosis, or delusional disorders) that do not have severe cognitive deficits.
The scores of various cognitive functions in individuals with schizophrenia range from .75 to 2.0 SD below the performance of the general population (matched for age and gender).9 This translates to dismally low percentiles of 2% and 24%. It is essential that all clinicians measure cognition in every patient with psychotic symptoms. It can be argued that cognition should even be measured in other psychiatric patients because cognitive deficits have been well documented in bipolar disorder, major depressive disorder, attention-deficit/hyperactivity disorder, and other disorders, albeit not as severe as in schizophrenia, and these deficits usually correlate with the patient’s vocational and social functioning.
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