Selective impairment of attentional networks of orienting and executive control in schizophrenia
Introduction
Recent theories have conceptualized attention as comprising three anatomically defined brain networks (Fan et al., 2003b, Posner and Petersen, 1990). The attentional component of alerting involves the ability to maintain the alert state tonically and the phasic response to a warning signal. It involves the cortical projection of the norepinephrine system (Marrocco and Davidson, 1998). The orienting network involves the selection of information from among numerous sensory inputs. The temporal parietal junction, superior parietal lobe and frontal eye fields are involved (Corbetta and Shulman, 2002). Blocking cholinergic input to the superior parietal lobe influences the ability to shift attention to cues (Davidson and Marrocco, 2000). Executive control of attention is involved in self-regulation of cognitions and emotions. It is most frequently measured by requiring a response to one aspect of a stimulus while ignoring a more dominant aspect. For example, to name the color a word is written in when the word spells a different color. The executive network involves the anterior cingulate cortex and lateral prefrontal cortical regions and is modulated by dopamine (Benes, 2000), with individual variations in executive attention related to genetic polymorphisms in genes related to dopamine (Diamond et al., 2004, Fan et al., 2003a, Fossella et al., 2002).
In various studies schizophrenic patients have been found to have a deficit in one or another of these attentional systems. Classical studies by Zahn et al. (1963) found that schizophrenic patients have trouble in responding well to warning signals, indicating an alerting deficit. In studies involving using cues to direct orienting to various locations it was shown that first break schizophrenic patients showed a specific deficit in orienting to stimuli on the right (Posner et al., 1988). Functional imaging studies have indicated a deficit in executive attention and abnormalities in activation of the dorsal anterior cingulate (Carter et al., 1997, Fletcher et al., 1999). These findings are with different patients and used different assays to probe the attentional deficit.
A method has been developed to assay the three attention networks within one experiment (Fan et al., 2002). The attention network test (ANT) provides a survey of the efficiency of the alerting, orienting and executive attention networks. Since the networks have been related to specific anatomy and neuromodulators, it would be useful to compare the performance of schizophrenic and control subjects in each of the networks using the attention network test. Accordingly we examined hospitalized patients with chronic schizophrenia on various neuroleptics with the attention network test in order to determine whether they would show generalized deficits in all attentional networks, or show specific deficits limited to the orienting and executive attention networks. We also examined the relationship between any deficits observed and variation on the patients' demographic and clinical characteristics, such as age, number of positive and negative symptoms, and duration of the disorder.
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Participants
The current study included 77 hospitalized schizophrenic participants who met DSM-III-R criteria for schizophrenia (American Psychiatric Association, 1987). They were recruited from Hefei Psychiatry Hospital affiliated with Anhui Medial University, the largest provincial psychiatric facility located in Anhui Province, China. The following inclusion criteria were met by all participants: (a) no demonstrable brain disease other than schizophrenia (i.e. no history of loss of consciousness and no
Demographic and clinical data
Schizophrenic patients aged between 17 and 57 years (mean = 28 years, 46 female and 31 male, 74 with right handedness and 3 left with handedness), and were educated for 5–15 years. Fifty-three normal controls were aged from 19 to 57 years (mean = 29 years, 27 female and 26 male, 51 with right handedness and 2 with left handedness) and educated for 5 to 15 years. There were no significant differences in age or years of education between the patient and the control groups. The mean duration of
Discussion
The attention network test appears to be very sensitive to attentional deficits in schizophrenic patients as it is in some other disorders (Fernandez-Duque and Black, in press, Posner, 2003, Posner et al., 2002, Sobin et al., 2004). The attention network test has the advantage of allowing for the comparison of the relative deficits in different attentional networks. In this sample of chronic, medicated schizophrenic patients there is a clear deficit in the executive network, related to the
Acknowledgement
This work was supported by National Natural Science Foundation of China (30370479), Scientific Research Foundation for the Returned Overseas Chinese Scholars ([2003]14), Anhui Province Extinguished Youth Science Grants ([2002]02), and Anhui Province Natural Science Grants (01043602, 2004kj192zd) to KW. The author JF would like to thank Dr. Jack M. Gorman and Dr. Kurt Schulz for their very valuable input.
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