Schizophrenia: Information Processing and Attention, Learning and Memory, Differential Diagnosis

Information Processing and Attention

The term information processing is used to describe the process of taking information and encoding it in such a way that it can be understood and recalled when appropriately cued. This construct is related to neural circuits and a stepwise logical spread of neu-rochemical messages, which may be impaired in schizophrenia. Attention, simply defined, is the ability to focus on a stimulus, either through conscious effort or passively. These two constructs are interrelated, and our understanding of their composite parts has increased in complexity in the past few decades.

Measures of attention were developed from the idea that patients with schizophrenia cannot block out unimportant stimuli in the way that those without schizophrenia can. This phenom-enon has come to be called gating. Gating is usually seen, for example, when a weak stimulus is delivered before a real stimu-lus. Normally, the first stimulus would dampen or eliminate the response to the second.

In general, patients with schizophrenia have impairments in information processing, especially when they are exposed to increasing demands on their attentional capabilities, such as un-der timed conditions or in stressful situations. Therefore, these deficits not only are viewed as trait linked (i.e., a manifestation of the illness itself) but may be compounded when state linked (i.e., when there are increases in symptoms). The trait-linked dis-turbances in neuropsychological parameters are seen in those at high risk for developing schizophrenia, those who have schizo-phrenia, and relatives who appear clinically unaffected, which may indicate a genetic vulnerability.

Many of these tests of attention and information process-ing have been associated with specific symptoms and neuropsy-chological impairment in schizophrenia. For example, one study showed that impaired prepulse inhibition was related to increased perseveration on neuropsychological tests of higher executive function (Butler et al., 1991). Others have shown that deficits in attention and information processing may be associ-ated with positive and/or negative symptoms (Strauss, 1993). Specifically, deficits in visual processing and motor function (as seen with continuous performance tasks) have been linked to negative symptoms (Nuechterlein et al., 1986), whereas positive symptoms seem to be related to auditory-processing dysfunction (Green and Walker, 1986)

Learning and Memory

Although there are generally no consistent gross deficits of memory in schizophrenia patients, close examination of certain aspects of learning and memory has revealed striking abnor-malities. Schizophrenia patients have been shown to be poorer in recall of word lists if the words are not grouped into catego-ries. Furthermore, unlike normal control subjects, schizophrenia patients do not seem to show an improvement in memory when asked to recall words with latent positive emotional meaning. These findings have been attributed to poor cognitive organiza-tion in schizophrenia patients.

Others have reported that patients with chronic schizophre-nia had impairment in new learning and short-term memory but not remote memory possibly indicating temporal–hippocampal dysfunction. These may be more likely in patients with a poor premorbid course and ventricular enlargement.

Working memory is a cognitive system that stores and processes information needed for planning and reasoning for a brief duration. Some cognitive scientists refer to short-term memory as working memory. Working memory consists of ver-bal and visual memory subsystems with a central principle that manipulates and coordinates information stored in the two sys-tems for problem solving, planning and organizing activities. Separate areas of the prefrontal cortex may underlie different aspects of the working memory. The workspace used for such memory is capacity-limited. Patients with schizophrenia have significant dysfunction in this area and are unable to change an ineffective strategy (i.e., shift sets) even when feedback is pro-vided. This dysfunction occurs (albeit at a lower level) even in subjects with higher intelligence. Conventional antipsychotics do not appear to impair or improve working memory in patients with schizophrenia. Studies involving evaluation of working memory using neuroimaging, pharmacological models of schizophrenia and neurochemical function should further our understanding of this manifestation of schizophrenia.

Differential Diagnosis

Making an accurate diagnosis of schizophrenia requires high levels of clinical acumen, extensive knowledge of schizophrenia and sophisticated application of the principles of differential di-agnosis. It is unfortunately common for patients with psychotic disorders to be misdiagnosed and consequently treated inappro-priately. The importance of accurate diagnosis is underlined by an emerging database indicating that early detection and prompt pharmacological intervention may improve the long-term prog-nosis of the illness.