Switching focus underlies attention problems in schizophrenia

Nov 13 2013

By Lucy Piper, Senior medwireNews Reporter

Impaired attention in patients with schizophrenia is related to difficulties in switching the focus of attention rather than in maintaining attention, researchers report.

They found that patients with schizophrenia performed worse on the attention-switching task of the Continuous Performance Task (CPTax), which involves responding to a target letter only when it appears in a certain sequence, than mentally healthy individuals.

However, their performance on a sustained attention task (CPTx), involving responding to a single letter irrespective of the sequence it appears in, was similar to that of mentally healthy individuals.

“If confirmed, [this] would support the idea that in schizophrenia the control of selection is impaired, while implementation of selection is intact,” say lead researcher Henderikus Smid (University of Groningen, the Netherlands) and colleagues.

In the attention-switching task, the 15 patients with schizophrenia had slightly more omissions (9.33 versus 1.87) and significantly longer response times (503 vs 435 ms) than 15 mentally healthy participants. They also had significantly smaller selection negativity (SN) amplitudes, which is a measure of the difference in event-related brain potentials in response to target and non-target stimuli and reflects the selective processing of relevant stimuli.

Indeed, the researchers note in PLoS One that there was an absence of detectable SNs for the relevant stimuli in the attention-switching task among the schizophrenia patients.

By contrast, the schizophrenia patients’ performances on the sustained attention task did not differ significantly from those of the mentally healthy individuals.

The findings “suggest that in schizophrenia the mechanisms that control the focus of selective attention have problems to change that focus on the basis of cues in a dynamic environment,” say the researchers.

In terms of daily life, this deficiency could underlie “cognitive slowness,” poor portrayals of the social environment, and impaired adaptation to changing daily tasks, they explain.

“Impairment of control over which information should be selected for a current goal may also be related to the emergence of delusions, the experience of hallucinations, and negative symptoms, which are the primary symptoms of schizophrenia,” they add.

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