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REVIEW ARTICLE
Year : 2012  |  Volume : 39  |  Issue : 2  |  Page : 57-63

Cognitive deficits in schizophrenia


Department of Psychiatry, KLE University's J.N. Medical College, Belgaum, India

Date of Web Publication1-Oct-2012

Correspondence Address:
S Chattopadhyay
Department of Psychiatry, KLE Hospital, Belgaum 590 010
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0974-5009.101842

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  Abstract 

The term schizophrenia was coined by Eugene Bleuler. Symptoms of schizophrenia are arranged into groups or clusters called as domains. The domains of dysfunctions are positive symptoms, negative symptoms, cognitive impairments, mood and suicidity, and aggression. Cognition is the sum total of mental processes that makes us acquire knowledge and keeps us aware of our surroundings and thus enables us to arrive at appropriate judgments. Cognitive deficits are recognized as enduring and persistent features in schizophrenia and can be neuro-cognitive or relating to social cognition. Neurocognitive deficits are deficits in speed of processing, attention / vigilance, working memory, verbal memory, visual memory, reasoning and problem solving, social cognition. Cognitive function can be assessed by various methods like experimental approach, neuropsychological and psychometric and ecologic approach. Cognitive deficits are present at onset of illness producing substantial impairment. Unlike psychotic symptoms, which remit with treatment, functional impairments remain stable over time. Detail understanding of such symptoms will help in disability limitation. Various cognitive remediation programmes are underway with such intent. Articles till March, 2012 were searched through PubMed and Google Scholar, which were studied in an attempt of understanding the topic. The information was structured and organized.

Keywords: Attention, cognition, cognitive dysfunction, cognitive remediation, schizophrenia, vigilance


How to cite this article:
Chattopadhyay S, Patil N M, Nayak R B, Chate S S. Cognitive deficits in schizophrenia. J Sci Soc 2012;39:57-63

How to cite this URL:
Chattopadhyay S, Patil N M, Nayak R B, Chate S S. Cognitive deficits in schizophrenia. J Sci Soc [serial online] 2012 [cited 2019 Oct 13];39:57-63. Available from: http://www.jscisociety.com/text.asp?2012/39/2/57/101842


  Introduction Top


Schizophrenia is characterized by distorted thinking and perception, inappropriate or blunted affect in clear consciousness and intellectual capacity though later cognitive deficits might evolve. [1] For centuries, the Greek physicians knew of a disease characterized by delusion, paranoia, deterioration in cognition, and personality. Kraepelin described dementia precox as a disease that had early onset, a deteriorating course with hallucinations and delusions and cognitive changes. [2] The term schizophrenia was coined by Eugene Bleuler who stressed that deteriorating course may not be universal. [3] He described 4 A s as symptoms: Loosening of association, affective disturbance, autism, and ambivalence. A rough estimate of the incidence in Indian population is about 4 per 10,000. [4] The worldwide point prevalence is about 4.6/1000 population. [5]

Domains of symptoms in schizophrenia
Symptoms of schizophrenia are arranged into groups or clusters called as domains. The domains of dysfunctions are positive symptoms, negative symptoms, cognitive impairments, mood and suicidity, and aggression. [6] The pattern of dysfunction in different domains is independent and varied in etiology, pathogenesis, and their response to treatment. Positive symptoms include new behaviors generated by neuropsychological system like disorder of thought, delusions, hallucinations, and movements. [7] Negative symptoms are deficits and functional impairments produced by progression of disease process. [8] Clustering of symptoms helps in better understanding and management.

Cognition
Cognition is the sum total of mental processes that makes us acquire knowledge and keeps us aware of our surroundings and thus enables us to arrive at appropriate judgments. [9] In simple terms, cognition is thinking and involves acquiring information, processing the acquired information, and arriving at certain conclusions to take action. It is cognition, which determines skills like problem-solving, decision-making, and creativity. The initial models of psychology were insufficient to explain the complex behavior patterns of organisms. Understanding cognition provides an insight into complex pattern of human behavior. [10] Thus, with better understanding, the implication of cognition is broadening and is expected to gain more importance in the days to come.

Broadly, cognition can be divided into 2 broad categories- neurocognition and social cognition. Neurocognition is the process of cognition involving distinct brain areas and particular neural circuits. Social cognition includes those set of cognitive processes involved in interaction with the social world. [11] It involves processing information of self and surroundings with respect to social norms. It requires understanding the expression of others and producing responses appropriate to reciprocate. Thus, it forms an essential part for functioning in society appropriately.

The process of cognition is complex and a multistep process. It involves selection of information from the environment, modification of the information, making appropriate associations among them. [12] This information so processed may be stored in the brain and may be retrieved and reanalyzed later. Further, with experience, the pattern of processing information changes and may result in learning. For cognition, an information is usually stored in a neuron as memory, and it is suggested that it is processed by the same neuron that had processed during encoding for proper cognition. [13]

Processing of information is a multistep complex task involving perceiving stimuli about the environment, selecting appropriate information from the environment, processing by analyzing, and thinking. [14] The information is evaluated with respect to existing situation and compared to prior experience. These steps culminate in judgment and appropriate action. A copy of it is also stored for retrieval in future. [15]

Cognitive theory of learning says that thoughts determine our behavior. The pattern of information processing is unique for each individual and determines his way of thinking and how an individual behaves. Cognition also determines various personality traits and thus has an impact on the ability. Thus, cognition is an important factor, which determines the level of performance. [16]

The theory of cognitive development describes nature and development of human intelligence proposed by Piaget. He described reality to be a dynamic process and characters represented as certain connotations and symbols that lead to specific thought processes or cognitive development. He proposed the concept of assimilation and accommodation. Assimilation is the way of receiving new information from the environment, and accommodation is how it relates to the internal state of the organism. In schizophrenia, the process of cognition is disorganized leading to cognitive symptoms. [17]

Cognitive deficits
Basically, cognition implies processing of information. The main neurocognitive functions are information processing, attention, executive function, comprehension, learning, and memory. [18] These functions can be assessed by testing for orientation, solving problems, abstract thinking, learning new skills, and make judgments. [19] Inadequacies in these faculties produce deficits detrimental in schizophrenia.

In the beginning of 20 th century, even before the introduction of the term schizophrenia, deficits of cognition have been known to be a feature of this illness. Kreplin in his classic book DEMENTIA PRAECOX AND PARAPHRENIAS describes about these deficits. [2] Bleuler had also described cognitive deficits as enduring features. [20] Though cognitive deficits are known to be present in schizophrenia from the beginning, they had been in back stages for years. Initially, psychoanalytical theory of Freud was highly regarded for and was sought for explanation of disease symptoms. With the advent of antipsychotics and the remarkable effects it produced, they remained in limelight for years. However, it came to attention that these typical antypsychotics, though controlled the positive symptoms left the cognitive deterioration unchecked.

Cognitive deficits are recognized as enduring and persistent features in schizophrenia and are related with different level of disease process. [21] In the recent years, National Institute of Mental Health U.S.A., Division of Mental Disorders initiated and funded workshops named Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS). [22] As identified by NIMH-MATRICS, the different domains of cognition that are impaired in schizophrenia are speed of processing, attention / vigilance, working memory, verbal memory, visual memory, reasoning and problem solving along with social cognition.

Schizophrenia is a disease characterized by persistent functional impairments. Although neurocognitive deficits have been known to be present in schizophrenia, how they impact functioning remains yet to be studied in detail. [23] The extent and nature of impairment varies from patient to patient as can be explained from the underlying structures involved. Most of the interest so far has been centered around describing and quantifying the deficits rather than accessing how they might impact functional outcome. Currently, cognitive deficits have been found to be related to functional outcome. [24]

Cognitive deficits in schizophrenia have been found to correlate with other symptom domains in schizophrenia. The extent of deficits, especially in memory and executive function, has been found to be more in disorganized type and in those with predominance of negative symptoms while subjects with predominance of positive symptoms had better preservation of these functions. [25] The patients with negative symptoms had exhibited inabilities to plan and organize. This pattern of inability has been found unrelated to the severity of the illness.

Impairments have been found to be present often before the first episode of the illness and have been found to persist even after recovery. [26] Some of the recent literatures mention it to be in the range of 97-98%. [27] Such deficits have also been found to be present in blood relatives of such patients. [28] A better understanding and insight into the pattern of deficits can help in better treatment.

Relation of cognition with other investigations
Today, it is a well-established fact that cognitive deficits are produced as a result of abnormalities of underlying structures of various brain areas. Electroencephalograph shows multiple changes in schizophrenic patients with less alpha activity and more of slow wave activity. [27],[29]

P300 is an evoked response potential produced in response to a target stimulus when presented with a set of non-target stimuli. [30] These markers have been found to correlate with cognitive deficits and may be an excellent way of early detection and effective treatment. [31]

In multiple studies, there have been varied responses to visual and auditory stimuli. These are evoked potentials in response to target stimuli. Such responses are specific to different areas of brain and correlate with the pattern of cognitive impairment. [32]

Eye movement abnormalities are common in patients of schizophrenia. Two commonest abnormalities are those of smooth-pursuit eye movement and anti-saccade performance. [33] Such abnormalities are also noted in unaffected relatives of patients of schizophrenia. [33] Cognitive impairments have been found to coexist with eye movement abnormalities, suggesting a possible anatomic correlation. [34]

Cognitive deficit assessment
Cognitive function can be assessed by various methods. The approaches can be an experimental approach, neuropsychological and psychometric, and ecologic approach. [35]

In neuropsychological method, psychological tests are put to use and statistical concepts are applied on the result. However, any single test is far from adequate in measuring all components of a deficit, hence a battery of tests are needed. [36] Experimental approach involves computing performance and controlling confounding variables. These methods though helpful in identifying disabilities fail to make actual assessments. Ecological approach involves performance in unstructured and unconstrained environment and has the advantage of assessment in real life scenario.

Deficits in cognition are slowly developing over the course of illness and may even persist even after disease remits. Initial abnormalities include minute pathologies that can be detected by sophisticated methods like electroencephalogram, tracking of eye movement patterns, and functional imaging. Subsequently, deficits increase to produce impairments such as reduced attention span. These can be detected by ordinary cognitive function tests. Further progress causes inability to perform day-to-day activities properly like reading newspaper. If unchecked, they go to make the patient handicapped. [35]

Deficits also have implication on prognosis. Deficits in executive function and working memory are known to produce maximum impairments. Early detection and intervention may be beneficial in disability limitation and better prognosis. [37]

Details of cognitive deficits and its anatomical correlates
Working memory

It is that capacity of human memory that holds information about recent stimuli, abstract methods to process it and arrive at a predetermined goal. It involves repeated processing and analyzing of information. It plays an important role in functions of cognitive processes of reasoning and acquiring information. It involves holding an information for a short time and using it to undertake a cognitive task by a network of memory systems. [38] An example to describe would be finding a telephone number from the telephone directory, keeping it in mind, plan what is to be spoken, and retrieving the number and dialing it.

Prefrontal cortex is involved in working memory. Magnetic resonance studies in patients with schizophrenia show reduced blood flow in inferior frontal gyrus. [37] This is proximate to speech area and may also be connected. Working memory involves verbal to spatial association. [39] Patients with schizophrenia have spatial memory deficits, similar to patients of frontal lobe lesion. [40] Working memory system is of more limited capacity in patients with schizophrenia.

Working memory deficits are related to symptoms of schizophrenia. Studies show that visuo-spatial and working memory correlate inversely with negative symptoms. Patients tend to perform poorly on spatial span tests. [41]

Executive function
It is a complex cognitive process that involves using several sub-processes to achieve a particular goal. [42]

It is a broad area of function involving various processes and subprocesses. It includes the total process of that occurs from the origin of abstraction thought or perception of stimulus to planning of the task at hand and arriving at a predetermined goal. It involves minute processes such as planning action, solving problem, behavior modification with change in environment, arranging a complicated task into a decided sequence. These are most important in dealing with any kind of task, from simple to complicated.

Frontal cortex is the predominant structure involved in executive function. Performance in executive functions is determined by frontal lobe. [43] Patients with damage to frontal lobe, frontal lobe syndrome suffer from executive function deficits. [44] Proper execution is not only limited to frontal cortex but also involves several sub-cortical structures. Neuroimaging studies localize prefrontal area as a region involved in cognition. [42] Involvement of cortico-striatal pathway in patients of Huntington's disease produces executive function deficits. [39]  Parkinsonism More Details demonstrates marked symptomatic differences from schizophrenia. However, they have similarities in problems of mentation they demonstrate. Fronto-striatial abnormalities are thought as an explanation for these deficits. [45]

Executive function deficits are found to correlate with intensity of negative symptoms like alogia, affective flattening to the severity of the illness, and absence of insight. [46] Violent and self-injurious behavior correlates with insight, hence with cognitive deficits. [47] Deficits of executive function have also been found in parents of schizophrenic patients. [48]

Often, patients of schizophrenia perform worse than what their level of intelligence will predict. It is thought that functional impairment may be related more to deficits of execution than to intelligence. Thus, executive function deficits may be more related to functional outcome.

Attention
The process that selects certain inputs from the environment for inclusion in the focus of experience is attention. In the process of attention, an object is selected from the environment, which is focused onto neglecting others and putting in margin. [12] The capacity of human mind is limited; therefore, it is unable to process whatever stimulus reaches it from the environment but can only process certain selected stimuli. Attention is the ability to select and focus on a stimulus relative to others. This ensures precise activity and a goal-oriented approach, proper judgment, and decision-making.

Deficits in attention are present in patients of schizophrenia. Even relatives and patients with schizotypal personality also have attention impairments. [49] Attention requires rapid encoding of information. In schizophrenia, perhaps rapid encoding of information is deficient leading to attention impairments. [50] Attention varies according to age, sex, and education level. [51] Implying the fact that environment and training may help improve attention.

Prefrontal cortex appears to be involved in schizophrenia. Functional magnetic resonance studies show the right mesial prefrontal cortex, the right cingulate, and the left thalamus to be predominant areas involved in patients of schizophrenia with attention impairments. [44]

In patients of schizophrenia, deficits of attention are global with difficulty to focus on any kind of stimulus, spatial and verbal. In schizophrenics, attention remains constant over time and deficits persist even after the improvement of illness. [52] Hence, functional impairments persist in stable phase due to these underlying deficits.

Learning and memory
Memory is storage of information obtained from experiences of past. It involves obtaining information from surrounding, storing it, and retrieving it for use when needed. In schizophrenia, impacts on long-term memory are profound and impairing. Patients of schizophrenia initially take longer time to encode information than do normal people; however, they tend to perform better with repeated exposure. [53],[54] Patients of schizophrenia have impaired ability to transform verbal information into long-term memory. This is associated with impairment in early encoding process. These become more pronounced if attention is to be distributed. [55] These can be of help in teaching remediation process.

Memory dysfunction in schizophrenia is regarded as broad and general. [56] Deficits include impairments in recall like crude recall and immediate recall, type of stimuli like verbal and non-verbal, and retention interval like immediate and delayed. The extent of deficit varies as per the general intent of impairment. [56] Deficits of attention and working memory appear to be greater in schizophrenia and could impact learning and memory indirectly. [57]

Information processing is mainly by infra-temporal cortex. Projections from medial temporal lobe to medial thalamic structure and diencephalon to frontal lobe are important for conducting memory to action. [58] Encoding and consolidation deficits are produced due to hippocamal and temporal lobe dysfunction. [58]

Impact and handicap produced by memory impairment may be profound. Pharmacotherapy may require use of anti-cholinergics and benzodiazepines for side-effects of typical anti-psychotics, which may worsen these deficits further. [58] With greater understanding and extensive research, the importance of these domains is increasing and is expected to be an important factor in management decision.

Implications of cognitive deficits
Cognitive deficits are present at onset of illness producing substantial impairment. If treated early, patients fair well. Unlike psychotic symptoms, which remit with treatment, functional impairments remain stable over time. Impairments have been treated with behavior interventions. Recently, various cognitive remediation programmes have been put to use to control the problem.

Cognitive rehabilitation
Cognitive rehabilitation encompasses two main approaches; remediation and compensatory approaches. Initially applied for a verity of brain disorders, currently it is a main measure for disability limitation and treatment in schizophrenia. [59]

Cognitive remediation
Cognitive remediation can be defined as consisting of a set of cognitive drills or compensatory interventions designed to enhance neuropsychological functioning. [60]

Initially it was developed for remediation of brain injury but later on found useful in schizophrenia. [61] Main attempts include those targeting to correct motivation and social functioning. Models of remediation programs include measures those deficits to correct these. [62]

In recent years, cognitive remediation has become an area of active interest with several studies across demographic variables. The effect on overall cognition is significant, but that on visual learning and memory is not significant. [63] The effects are significant for functioning but not for symptoms. [45] Hours of training had no relation to effect. [63] Symtomatology remained unaffected though benefit in cognitive function was evident. [64] Cognitive remediation improves mood. [65] Patients who underwent cognitive remediation had better social and occupational performance. [66]

Cognitive Enhancement Therapy (CET), a therapeutic procedure combining activities, aimed at improving cognitive performan­ce. It involves interventions to boost resources in aspects related to perceptive and cognitive abilities, critical for the social functioning and general adjustment.

Correlates of cognitive function with functioning
Cognitive functions are required for proper functioning in day-to-day world. Cognitive deficits are predictive of functional outcome.

Working memory is required for occupational and social functioning. [21] Performance requires retention of a perceived stimuli and manipulating it towards a goal. In society to interact, we need to perceive it and produce appropriate response. Keeping track of tasks at hand, their onset and conclusion with prioritization requires working memory.

Executive function is important for occupational functioning and independent living. [38] Employment requires ability to plan, prioritize, and solve problems. It is required to plan for future and set goals for independent livelihood.

Sustained attention is needed for any kind of work; social to occupational. Ability to maintain attention helps avoid mistakes and in successful interaction.

 
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