Brief reportResponse inhibition and impulsivity in schizophrenia
Introduction
Schizophrenia is characterized by disturbances of cognition, emotion, perception, and behavior (American Psychiatric Association, 2000). Neurocognitive studies suggest an array of impairments, particularly concerning frontal/executive abilities (Pantelis et al., 1997, Hill et al., 2004, Shad et al., 2006, Twamley et al., 2006). Response inhibition plays a crucial role in executive functioning (Barkley, 1997) and is linked to impulsivity (Logan et al., 1997); it may therefore be particularly relevant to schizophrenia.
Response inhibition is typically measured via a stop task, which is based on Logan's (1994) ‘race’ model. It allows measurement of both the speed of behavioral inhibitory (stopping) processes, and the ability to effectively trigger inhibitory processes. While there have been few stop task investigations of schizophrenia (and none in the context of possible behavioral consequences, such as impulsivity), evidence suggests that there are impairments in the triggering of inhibitory processes, but that speed of inhibitory processes (when triggered) is relatively unaffected (Badcock et al., 2002). Note, however, that the nature of inhibition in schizophrenia is controversial (Bellgrove et al., 2005), and such deficits are not universally reported (Rubia et al., 2001).
Consistent with frontal dysfunction accounts of schizophrenia (Hill et al., 2004), dorsal and ventral prefrontal regions have typically been implicated in response inhibition (Blasi et al., 2006). Indeed, there is recent evidence for a specific response inhibition role for the right inferior frontal gyrus (rIFG; Chambers et al., 2006), but pathways involved may differ between healthy individuals and those with schizophrenia (Ford et al., 2004). Hoptman et al. (2002) found a relationship between white matter abnormalities in rIFG and motor impulsiveness in men with schizophrenia, and more recently suggested that impulsivity in schizophrenia results from dysfunction of fronto-temporo-limbic circuitry (Hoptman et al., 2004).
The current study investigates stop task inhibition among adults with schizophrenia, and examines associations with self-reported impulsivity. Thus, we aim to provide further evidence concerning the nature of impaired response inhibition in schizophrenia (i.e., impaired triggering and/or slower inhibitory processes), and determine whether such impairments are linked to patients' ratings of their own impulsiveness.
Section snippets
Participants
Eighteen inpatients (13 males; mean age: 36.11 [10.78]; mean IQ: 104.56 [10.76]) with DSM-IV schizophrenia were recruited from acute and non-acute (i.e., rehabilitative) wards at a secure psychiatric hospital. Diagnostic interviews were completed by a psychiatrist. All were receiving neuroleptic medication (clozapine [44%], olanzapine [22%], arirpiprazole [17%], quetiapine [11%], and risperdone [6%]), while 14 had a history of substance use (urine analysis indicated that none were presently
Results
Summary data are presented in Table 1. As expected, analysis of variance (ANOVA) revealed that patients with schizophrenia displayed significantly increased attentional impulsiveness, F(1,33) = 4.33, P < 0.05, motor impulsiveness, F(1,33) =6.84, P < 0.02, nonplanning impulsiveness, F(1,33) = 4.67, P < 0.04, and total impulsiveness, F(1,33) = 7.71, P < 0.01, compared with the control participants.
Stop task outcome measures (i.e., stop signal reaction time, inhibition functions) were calculated according to
Discussion
These results provide further evidence for response inhibition impairment in schizophrenia, supporting the view that such inhibitory dyscontrol is a key neurocognitive deficit of the disorder. In the current study, this impairment was characterized by slower inhibitory processes, but (inconsistent with Badcock et al., 2002) in the context of intact triggering of inhibitory processes. Interestingly, however, stop signal reaction time among patients with schizophrenia was not associated with
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