Schizophrenia is characterized not only by a number of clinical symptom but also by board cognitive impairment deficiency in a few elementary functions may underlie impairment in various neuropsychologic domains as well as impede daily-life functioning is woking memory according to baddeley’s model working memory is in charge of the simultaneous manipulation and storage of the information the central executive component of working memory which involves attentional and inhibitory processes enable the manipulation of the information working memory is trus distinct from short-term memory which merely ensures storage an impaired working memory has been established in patient with schizophrenia and proposed as a core deficit underlying a board rang of neurocognitive dysfunctions another possible mechanism is decrease processing speed which has emerged as an important cause of various types of cognitive impairment in these patients slowing is a consistent feature of patient with schizophrenia and affect both the motor and that cognitive speed shares a common factor with the central executive component of working memory.
Considering the potentially crucial role of both working memory and processing speed in cognitive efficiency and functional outcome it is important to determine the exe=tent to which deficit in these function is related to clinical symptoms negative symptom has been repeatedly shown to affect t neuropsychologic and cognitive functioning schizophrenia severity of depression is known to be a factor of cognitive impairment in various population depression is frequently impairment in various population depression is frequently observed in schizophrenia patients this symptom might similarly contribute to working memory and processing speed dysfunction
A test commonly used to measure the verbal working memory capacity is the backward digit span which requires repeating increasingly long series of digits in reverse order the task implie some mental manipopulation of the item and thus involves the central executive component of working memory by contrast the forward digit span which merely requires repeating the item in the same order solely reflect the storage capacity digit span is significantly reduced in patient with schizophrenia impaired backward digit span was associated with negative symptom in several studie but not in other verbal working memory can also be assessed using the letter –number sequencing span this task require reordering the letter and digits before repeating them and there fore puts an increased demand on the central executive the letter-number sequencing span was associated with negative symptom in parry et al and twamley et al but not in pukrop ey al Horan rt al A near -0 correlation was reported in anathor sizeable schizophrenia sample. Thus, the association between negative symptom and verbal working memory span is controversial.
A potential association between verbal working memory and depression in schizophrenia has been investigated in a few studies with convergent result No association between depression score and backward digit span was revealed in silver et al or twamley et al in previous research by our group severity of depression was significantly correlated with several measure of verbal memory efficiency but unrelated to the backward digit span A similar pattern of association with verbal memory score but not with the backward digit span was report by Moser et al
In this study we investigated the verbal working memory deficit and decrease of motor and cognitive speed in patient with schizophrenia, as well as the relationship between working memory and motor/cognitive speed the backward digit span was used to assess working memory. The backward digit span was used as a comparison measure, to demonstrate the specificity of the distinction between motor and cognitive speed. The trail making test –A and stroop color naming times were used to assess motor speed, whereas the digit symbol substitution test score was used for cognitive speed. We tested the hypothesis that working memory span and processing speed share a cognitive, as opposed to motor speed. By contrast, no association between forward digit span and cognitive speed was expected
We then used regression analyses to study the associations of negative symptom and depression with working memory span and processing speed. Premorbid intellectual level as assessed by the National Adult Reading Test (NART)was also entered as a predictor, to control for its effect .Intellectual level is likely to have a strong influence on cognitive efficiency, and might confound the association with clinical symptom. Potential association of negative symptom with working memory span and both motor and cognitive speed were explored. With regard to depression, we hypothesized on the basis of previous findings that it was associated with decrease in motor and cognitive speed, but not with reduced working memory span.