Neurocognitive functioning and suicidality in schizophrenia spectrum disorders
Introduction
Suicide is the single most important cause of premature death among patients with schizophrenia [1]. It is estimated that 5% of patients with schizophrenia die by suicide [2]. Suicidal thoughts and attempts occur in as many as 50% of patients [3], and previous attempted suicide is a significant risk factor for completed suicide [4].
Neurocognitive impairment is an important component of schizophrenia [5]. Deficiencies seen in a variety of neurocognitive domains, including memory, working memory, vigilance, and executive functioning, contribute to difficulties in managing daily activities [6]. Suicidality in schizophrenia has been associated with higher IQ [7], [8], but not consistently [9], [10], [11]. IQ is a measure of global cognitive function, and few studies have investigated the relationship between more specific neurocognitive domains and suicidal behavior in schizophrenia. Potkin et al [11] did not find a relationship between any specific neurocognitive domains and suicidality. Kim et al [9] found that patients with a history of lifetime suicidality performed better than patients without lifetime suicidality on measures of psychomotor speed, attention, working memory verbal fluency, verbal memory, and executive function, but this difference was mediated by feelings of hopelessness. Finally, Nangle et al [10] found that suicide attempters had better functioning than non-attempters on subcomponents of executive functioning (attention and verbal fluency). Executive function includes volition, planning, purposive action, and self-monitoring of behavior [12]. As impairment in executive processes could result in failure to formulate, plan and choose goal-directed actions, Nangle et al [10] have suggested that better executive functioning could imply better abilities to plan and initiate suicidal acts.
Impulsivity has also been hypothesized to predispose for suicidal behavior [13]. The conceptualization of impulsivity varies, but there is some agreement that the general features of impulsive behavior include rapid, spontaneous, ill planned, excessive, and potentially maladaptive conduct [14]. An association between increased behavioral impulsivity and suicidality has been indicated in patients with schizophrenia [7]. In addition, personality measures of impulsivity have been associated with increased suicidal risk in several psychiatric disorders [15], including schizophrenia [16], though not consistently [17]. It has been suggested that the use of neuropsychological measures of impulsivity could prove to be more sensitive [13] and objective [14] than clinical measures. The ability to inhibit inappropriate responses is a key component of executive function [18], and dyscontrol of inhibition is suggested to be a possible underlying cause of impulsivity. Hence, neuropsychological measurements of impulsivity commonly involve paradigms in which inappropriate responses must be inhibited [14]. A recent study found a relationship between inhibitory dyscontrol and personality measured impulsivity in a non-clinical sample [19]. Furthermore, impaired inhibition has been related to suicidality in different samples, including samples of bipolar disorder and mixed psychiatric disorders [20], [21], [22], [23], [24]. To our knowledge, no studies of this relationship have focused solely on patients with schizophrenia.
A model of suicidal behavior has been proposed in which the risk for suicidal acts is influenced by individual trait-like predispositions [13]. As neurocognitive impairments in schizophrenia are considered to be relatively stable over time [25], neurocognitive differences between suicide attempters and non-attempters could elucidate trait differences that predispose for suicidal acts. However, since impaired neurocognitive functioning has been related to current suicidal state, investigation of the relationship between lifetime suicide attempts and neurocognitive traits needs to consider the possible confounding effect of current suicidality [26].
The present study included a large group of consecutively recruited patients with schizophrenia spectrum disorders in different phases of illness and with heterogeneity in both suicidal- and other clinical symptoms. The primary aim of the study was to investigate whether lifetime suicide attempters had better global cognitive functioning (higher IQ), better executive functioning, or higher impulsivity (poorer inhibitory control) than non-attempters. The possible confounding effect of current suicidality on the relationship between neurocognitive performance and lifetime suicide attempts was taken into account.
Section snippets
Participants
The present study included a subsample from the ongoing Thematic Organized Psychosis Research (TOP) study. The TOP-study is a large translational research study at the Oslo University Hospital and the University of Oslo, Norway. The present patient sample was recruited from May 2003 until September 2007 from the 3 major hospitals in Oslo, covering a catchment area of 485 000 inhabitants (88% of the total population of Oslo), both inner city and suburban areas, and representing fairly well the
Results
Demographical and clinical variables in patients with (n = 53, 30.5%) and without (n = 121, 69.5%) lifetime suicide attempts are presented in Table 1. There were statistically significant group differences in gender, diagnosis, age at illness onset, duration of illness, depressive episodes, insight, PAS social functioning change, and use of sedatives. There were no significant differences in any neurocognitive domains between lifetime suicide attempters and non-attempters (Table 2). There were
Discussion
Contrary to our expectations, we found that suicide attempters neither had significantly higher IQ, better executive functioning, nor higher impulsivity (poorer inhibitory control) than non-attempters. Furthermore, the groups did not differ in motor functioning, psychomotor tempo, attention, or memory. These findings indicate that neurocognitive traits are not an essential part of a predisposition for suicidal acts in patients with schizophrenia spectrum disorders.
Our findings are thus
Acknowledgment
The study was supported by grants from the Research Council of Norway (#167153/V50, #163070/V50) and the South-East Norway Health Authority (#2004123, #2006258, and #2007004). The authors thank the patients for participating in the study, and the TOP study group members for contributing with data collection. We also wish to thank the Psychiatric Emergency Ward at the Oslo University Hospital (Aker) for their cooperation in making this work possible, and MSc Greg Reckless for help with language
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