Mixing apples with oranges: Visual attention deficits in schizophrenia

Modulation of hemispheric asymmetry in executive control of attention in schizophrenia with atypical antipsychotic treatment: Potential benefits of olanzapine

Deficits in executive control of attention have been reported in schizophrenia patients, but can be ameliorated by treatment of atypical antipsychotics along with the symptoms. However, it remains unclear whether this effect is related to a modulation of hemispheric asymmetry in executive control by the medicine. In this behavioral study, we employed a lateralized version of the attention network test to examine the hemispheric asymmetry of executive control in schizophrenia patients before and after olanzapine treatment, compared to matched healthy controls. Executive control was measured as a conflict effect, indexed as the response time (RT) difference between incongruent versus congruent flanker conditions, and was compared between stimuli presented in the left and the right visual field (i.e., processed by right versus left hemisphere of the brain). Results showed that pre-treatment schizophrenia patients revealed a right hemisphere superiority in conflict effect (i.e., a smaller effect in the right hemisphere than in the left hemisphere), driven by the incongruent condition. Olanzapine treatment reduced this right hemisphere superiority by improving the efficiency of the left hemisphere in the incongruent condition. These results suggested that olanzapine treatment may improve the efficiency of executive control in the left hemisphere in schizophrenia patients.

Attention in schizophrenia: Impaired inhibitory control, faulty attentional resources, or both?

While the literature regarding the existence of difficulties in inhibition in schizophrenia is relatively consistent, it is not clear whether these difficulties reflect any specific deficit in an inhibitory control process or whether they are the result of deficits in the systems that regulate inhibitory control, such as attentional resources. This also raises the issue of attentional resources in schizophrenia, which offers a somewhat puzzling and sometimes contradictory picture. In this study, these issues were investigated by means of a paradigm in which the need for inhibitory control and the need for correct allocation of attentional resources varied parametrically. Twenty-six outpatients with a diagnosis of schizophrenia and 26 matched controls completed a visual search task during which distractors were presented and had to be inhibited. At the same time, they also completed an auditory target detection task of varying difficulty. The results show that the patients had difficulties both in inhibiting distractors and in correctly allocating attention to the two tasks. The results also show that these two difficulties were not related. This leads to the conclusion that schizophrenia involves both defective inhibitory control and faulty management of attentional resources, and that the former does not result from the latter. Furthermore, these effects seem to be neither dependent on processing speed, nor related to medication.