Reaction time measures of sustained attention differentiate bipolar disorder from schizophrenia

Infraslow fluctuations of sustained attention in mood disorders

BACKGROUND

Sustained attention is integral to goal-directed tasks in everyday life. It is a demanding and effortful process prone to failure. Deficits are particularly prevalent in mood disorders. However, conventional methods of assessment, rooted in overall measures of performance, neglect the nuanced temporal dimensions inherent in sustained attention, necessitating alternative analytical approaches.

METHODS

This study investigated sustained attention deficits and temporal patterns of attentional fluctuation in a large clinical cohort of patients with bipolar depression (BPd, n = 33), bipolar euthymia (BPe, n = 84), major depression (MDd, n = 38) and controls (HC, n = 138) using a continuous performance task (CPT). Longitudinal and spectral analyses were employed to examine trial-level reaction time (RT) data.

RESULTS

Longitudinal analysis revealed a significant worsening of performance over time (vigilance decrement) in BPd, whilst spectral analysis unveiled attentional fluctuations concentrated in the frequency range of 0.077 Hz (1/12.90 s)-0.049 Hz (1/20.24 s), with BPd and MDd demonstrating greater spectral power compared to BPe and controls.

CONCLUSIONS

Although speculative, the increased variability in this frequency range may have an association with the dysfunctional activity of the Default Mode Network, which has been shown to oscillate at a similar timescale. These findings underscore the importance of considering the temporal dimensions of sustained attention and show the potential of spectral analysis of RT in future clinical research.

Understanding copy number variations through their genes: a molecular view on 16p11.2 deletion and duplication syndromes

Neurodevelopmental disorders (NDDs) include a broad spectrum of pathological conditions that affect >4% of children worldwide, share common features and present a variegated genetic origin. They include clinically defined diseases, such as autism spectrum disorders (ASD), attention-deficit/hyperactivity disorder (ADHD), motor disorders such as Tics and Tourette's syndromes, but also much more heterogeneous conditions like intellectual disability (ID) and epilepsy. Schizophrenia (SCZ) has also recently been proposed to belong to NDDs. Relatively common causes of NDDs are copy number variations (CNVs), characterised by the gain or the loss of a portion of a chromosome. In this review, we focus on deletions and duplications at the 16p11.2 chromosomal region, associated with NDDs, ID, ASD but also epilepsy and SCZ. Some of the core phenotypes presented by human carriers could be recapitulated in animal and cellular models, which also highlighted prominent neurophysiological and signalling alterations underpinning 16p11.2 CNVs-associated phenotypes. In this review, we also provide an overview of the genes within the 16p11.2 locus, including those with partially known or unknown function as well as non-coding RNAs. A particularly interesting interplay was observed between MVP and MAPK3 in modulating some of the pathological phenotypes associated with the 16p11.2 deletion. Elucidating their role in intracellular signalling and their functional links will be a key step to devise novel therapeutic strategies for 16p11.2 CNVs-related syndromes.

16p11 Duplication Disrupts Hippocampal-Orbitofrontal-Amygdala Connectivity, Revealing a Neural Circuit Endophenotype for Schizophrenia

Chromosome 16p11.2 duplications dramatically increase risk for schizophrenia, but the mechanisms remain largely unknown. Here, we show that mice with an equivalent genetic mutation (16p11.2 duplication mice) exhibit impaired hippocampal-orbitofrontal and hippocampal-amygdala functional connectivity. Expression of schizophrenia-relevant GABAergic cell markers (parvalbumin and calbindin) is selectively decreased in orbitofrontal cortex, while somatostatin expression is decreased in lateral amygdala. When 16p11.2 duplication mice are tested in cognitive tasks dependent on hippocampal-orbitofrontal connectivity, performance is impaired in an 8-arm maze "N-back" working memory task and in a touchscreen continuous performance task. Consistent with hippocampal-amygdala dysconnectivity, deficits in ethologically relevant social behaviors are also observed. Overall, the cellular/molecular, brain network, and behavioral alterations markedly mirror those observed in schizophrenia patients. Moreover, the data suggest that 16p11.2 duplications selectively impact hippocampal-amygdaloid-orbitofrontal circuitry, supporting emerging ideas that dysfunction in this network is a core element of schizophrenia and defining a neural circuit endophenotype for the disease.

Neural anomalies during vigilance in schizophrenia: Diagnostic specificity and genetic associations

Impaired vigilance is a core cognitive deficit in schizophrenia and may serve as an endophenotype (i.e., mark genetic liability). We used a continuous performance task with perceptually degraded stimuli in schizophrenia patients (N = 48), bipolar disorder patients (N = 26), first-degree biological relatives of schizophrenia patients (N = 55) and bipolar disorder patients (N = 28), as well as healthy controls (N = 68) to clarify whether previously reported vigilance deficits and abnormal neural functions were indicative of genetic liability for schizophrenia as opposed to a generalized liability for severe psychopathology. We also examined variation in the Catechol-O-methyltransferase gene to evaluate whether brain responses were related to genetic variation associated with higher-order cognition. Relatives of schizophrenia patients had an increased rate of misidentification of nontarget stimuli as targets when they were perceptually similar, suggestive of difficulties with contour perception. Larger early visual responses (i.e., N1) were associated with better task performance in patients with schizophrenia consistent with enhanced N1 responses reflecting beneficial neural compensation. Additionally, reduced N2 augmentation to target stimuli was specific to schizophrenia. Both patients with schizophrenia and first-degree relatives displayed reduced late cognitive responses (P3b) that predicted worse performance. First-degree relatives of bipolar patients exhibited performance deficits, and displayed aberrant neural responses that were milder than individuals with liability for schizophrenia and dependent on sex. Variation in the Catechol-O-methyltransferase gene was differentially associated with P3b in schizophrenia and bipolar groups. Poor vigilance in schizophrenia is specifically predicted by a failure to enhance early visual responses, weak augmentation of mid-latency brain responses to targets, and limited engagement of late cognitive responses that may be tied to genetic variation associated with prefrontal dopaminergic availability. Experimental results illustrate specific neural functions that distinguish schizophrenia from bipolar disorder and provides evidence for a putative endophenotype that differentiates genetic liability for schizophrenia from severe mental illness more broadly.

Exploring the Effects of an Acute Dose of Antipsychotic Medication on Motivation-mediated BOLD Activity Using fMRI and a Perceptual Decision-making Task

The left inferior frontal gyrus and the bilateral ventral striatum are thought to be involved in motivation-mediated decision-making. Antipsychotics may influence this relationship, and atypical antipsychotics improve secondary negative symptoms in schizophrenia, such as loss of motivation, although the acute effects of pharmacological medication on motivation are not fully understood. In this single-blinded, randomized controlled trial, 49 healthy volunteers were randomized into three groups to receive a single dose of haloperidol, aripiprazole or placebo. Between 4.0 and 5.6 h later, participant's brain blood-oxygen-level dependent (BOLD) activity was recorded using functional magnetic resonance imaging (fMRI) while completing a perceptual decision-making fMRI task consisting of one neutral and one motivated condition. Response bias, reflecting the participant's willingness to say that the target stimulus is present, was calculated using signal detection theory. Concurrent with widespread changes in BOLD signal in the motivated vs. neutral condition, a less conservative, mathematically optimal response bias was observed in the motivated condition across the whole sample. Within-group differences in BOLD signal in the left inferior frontal gyrus and bilateral ventral striatum were observed between conditions in the aripiprazole and haloperidol groups, but not in the placebo group. No robust between-group differences in brain activity in the left inferior frontal gyrus or the bilateral ventral striatum were found. Overall, we found no robust evidence for an effect of either aripiprazole or haloperidol on motivationally mediated behavior. An interesting pattern of correlations possibly related to pharmacologically induced alterations in the dopamine system was observed, although findings remain inconclusive and must be replicated in larger samples.

Effects of different types of sensory signals on reaching performance in persons with chronic schizophrenia

Previous studies have reported movement abnormalities in persons with schizophrenia. This study aimed to examine the differences between persons with chronic schizophrenia and healthy control participants in reaching movement and the effects of sensory signals on reaching performance in persons with chronic schizophrenia. A counter-balanced repeated-measures design was employed. Twenty persons with schizophrenia and 20 age- and gender-matched control participants were recruited in this study. Reaching performance was measured in three types of sensory signal conditions (visual, auditory, and no signal), i.e., two externally triggered and one self-initiated movement were assessed in reaction time/inter-response interval, movement time, peak velocity, percentage of time in which peak velocity occurred, and movement units. The results revealed significant main effects of group in reaction time/inter-response interval (p = 0.003), movement time (p < 0.001), peak velocity (p < 0.001), and movement units (p < 0.001). The persons with chronic schizophrenia demonstrated slower response to signals and in self-initiated movement, increased movement time, and less forceful and less smooth movement compared to healthy control participants when performing the reaching task. The interaction effect between group and signal in reaction time/inter-response interval was also significant (p < 0.001). The inter-response interval for self-initiated reaching was the shortest in healthy controls. Conversely, the inter-response interval for self-initiated reaching was the longest in persons with schizophrenia. The main effect of the signal on movement time was significant (p < 0.001). The movement time of reaching was longer in response to the auditory signal than in response to visual or self-initiated. The differences in percentages of time in which peak velocity occurred between persons with schizophrenia and healthy controls (p > 0.01) and across the three conditions (p > 0.01) were non-significant. Neither duration of illness nor antipsychotic dosage was significantly associated with reaching performance (all p > 0.01). In conclusion, these findings indicate that reaching movement in persons with chronic schizophrenia is slower, less forceful, and less coordinated compared to healthy control participants. In addition, persons with chronic schizophrenia also had shorter inter-response interval for self-initiated movement and shorter movement time in auditory signal condition, independent of duration of illness and antipsychotic dosage.

The putative lithium-mimetic ebselen reduces impulsivity in rodent models

BACKGROUND

Deficits in impulse control feature in many psychiatric conditions including bipolar disorder, suicidality and addictions. Lithium lowers impulsivity in clinical populations and decreases pathological gambling in experimental medicine studies, but suffers from adverse effects, poor compliance and a low therapeutic index.

AIMS

Recently we identified that the neuroprotective agent ebselen, which is reportedly safe in humans, inhibited inositol monophosphatase (IMPase), a candidate lithium mechanism. Ebselen also reduced 5-HT receptor (5-HT_2A) function which predicts impulsivity lowering properties. Here we investigated the effect of ebselen in rat models of impulsive behaviour.

METHODS

Ebselen was tested in two models of impulsivity with human analogues: the five-choice serial reaction time task (5-CSRTT) and rodent gambling task (rGT). The main outcome measures were premature responses (5-CSRTT and rGT) and choice behaviour (rGT), which model motor impulsivity and choice impulsivity, respectively.

RESULTS

At doses that decreased 5-HT_2A receptor function (DOI-induced wet dog shakes), ebselen decreased premature responding in the 5-CSRTT both in the absence and presence of cocaine. The 5-HT_2A receptor antagonist MDL 100,907 also reduced premature responding in the 5-CSRTT although not in the presence of cocaine. In the rGT ebselen showed a tendency to reduce premature responding but had no effect on choice behaviour.

CONCLUSIONS

These findings suggest that ebselen preferentially reduces motor impulsivity over choice impulsivity, and that inhibition of 5-HT_2A receptor function is a contributing mechanism. Collectively, these data support the repurposing of ebselen as an anti-impulsive treatment and fast-tracking to clinical trials in patient groups characterised by poor impulse control.

Sustaining attention to simple visual tasks: a central deficit in schizophrenia? A systematic review

Impairments in sustained attention, that is, the ability to achieve and maintain the focus of cognitive activity on a given stimulation source or task, have been described as central to schizophrenia. Today, sustained attention deficit is still considered as a hallmark of schizophrenia. Nevertheless, current findings on this topic are not consistent. To clarify these findings, we attempt to put these results into perspective according to the type of assessment (i.e., overall and over time assessment), the participants' characteristics (i.e., clinical and demographic characteristics), and the paradigms (i.e., traditionally formatted tasks, go/no-go tasks, and the sustained attention task) and measures used. Two types of assessment lead to opposite findings; they do not evaluate sustained attention the same way. Studies using overall assessments of sustained attention ability tend to reveal a deficit, whereas studies using over time assessments do not. Therefore, further research is needed to investigate the underlying cognitive control mechanisms of changes in sustained attention in schizophrenia.

The role of encoding strategies in contextual memory deficits in patients with bipolar disorder

Contextual memory is important for the encoding and retrieval of episodic memory, which is often impaired in euthymic patients with bipolar disorder (BD). The objective was to investigate the effect of low and high cognitive support on encoding in an incidental contextual memory task in euthymic patients with BD. Twenty-three patients with a BD type I diagnosis (aged 23-63 years, 17 women and 6 men) and 29 healthy controls completed a recognition memory task for context (location of a recognised object). Participants were assigned to one of two incidental encoding conditions: (1) with a binding cue to encourage the association of the object to its location (judging the degree of appropriateness of an object in relation to its location) or (2) without a binding cue (judging daily use of objects). Patients showed a deficit in incidental contextual memory in the absence of a binding cue at encoding. Under incidental encoding with the binding cue, no differences were observed between the groups for contextual memory. Contextual memory deficits in BD patients were reduced by providing cognitive support at encoding. The role of this strategy should be investigated in larger samples to evaluate its use for cognitive remediation in BD patients.

P300 aberration in first-episode schizophrenia patients: a meta-analysis

BACKGROUND

Decreased P300 amplitude is one of the most consistent findings in patients with schizophrenia. However, whether prolonged P300 latency occurs in patients with schizophrenia, especially first-episode schizophrenia (FES) patients, remains controversial.

METHODS

A meta-analyses of P300 aberration in FES patients and healthy control(HC) group was conducted. The meta-regression analysis was performed using a random effects model. The pooled standardized effect size (PSES) was calculated as the division of the difference between the means of the two groups by the common standard deviation.

RESULTS

A total of 569 FES patients and 747 HCs were included in this meta-analysis. P300 amplitude was significantly reduced (PSES = -0.83, 95% CI: -1.02-0.65, P = 0.00001) and P300 latency was delayed significantly in FES patients (PSES = -0.48, 95% CI: 0.14-0.81, P = 0.005). The meta-regression analysis showed that task difficulty was a source of heterogeneity.

CONCLUSIONS

The meta-analysis confirms that disrupted information processing is found in FES patients, which is manifested by smaller P300 amplitude and delayed P300 latency.

Performance monitoring and executive control of attention in euthymic bipolar disorder: employing the CPT-AX paradigm

Reduced cognitive test performance has been demonstrated in patients with bipolar disorder (BD), even when euthymic. Several studies have explored aspects of attention, including sustained attention, and reported patients show lower accuracy compared to controls. It is necessary to modify existing attentional paradigms to fully characterise such deficits. The present study sought to examine if there are changes in the profile of performance and error-types during a sustained attention task in BD. Twenty-two euthymic patients with DSM-IV diagnosed BD and 21 healthy controls were recruited. Participants completed a modified CPT-AX paradigm with a high proportion of target trials (70%) with cues and probes presented at continuous intervals. This modification increases the demands on response inhibition and permits the deconstruction of attentional/executive deficits previously described. Overall, BD patients showed significantly poorer target discriminability compared to controls. In block one (first quarter) of the task, patients showed no significant differences to controls, but by the final fourth block (last quarter) they made significantly fewer hits and more errors (both 'AX' misses and 'BX' false alarms). BD patients completed initial stages of the task similarly to controls, but as demands on the attentional system continued difficulties emerged, consistent with problems in context-maintenance.

Pre-attentive information processing and impulsivity in bipolar disorder

Early responses to stimuli can be measured by sensory evoked potentials (EP) using repeated identical stimuli, S1 and S2. Response to S1 may represent efficient stimulus detection, while suppression of response to S2 may represent inhibition. Early responses to stimuli may be related to impulsivity. We compared EP reflecting stimulus detection and inhibition in bipolar disorder and healthy controls, and investigated relationships to impulsivity. Subjects were 48 healthy controls without family histories of mood disorder and 48 with bipolar disorder. EP were measured as latencies and amplitudes for auditory P50 (pre-attentional), N100 (initial direction of attention) and P200 (initial conscious awareness), using a paired-click paradigm, with identical stimuli 0.5 s apart. Impulsivity was measured by questionnaire and by laboratory tests for inability to suppress responses to stimuli or to delay response for a reward. Analyses used general linear models. S1 amplitudes for P50, N100, and P200, and gating of N100 and P200, were lower in bipolar disorder than in controls. P50 S1 amplitude correlated with accurate laboratory-task responding, and S2 amplitude correlated with impulsive task performance and fast reaction times, in bipolar disorder. N100 and P200 EP did not correlate with impulsivity. These findings were independent of symptoms, treatment, or substance-use history. EPs were not related to questionnaire-measured or reward-based impulsivity. Bipolar I disorder is characterized by reduced pre-attentional and early attentional stimulus registration relative to controls. Within bipolar disorder, rapid-response impulsivity correlates with impaired pre-attentional response suppression. These results imply specific relationships between ERP-measured response inhibition and rapid-response impulsivity.

Bridging the bench to bedside gap: validation of a reverse-translated rodent continuous performance test using functional magnetic resonance imaging

Vigilance, which requires attending to relevant while ignoring irrelevant stimuli, is a cognitive domain impacted by schizophrenia and bipolar disorder. Various continuous performance tests (CPT) have been used to examine neural correlates of vigilance within people with and without severe mental illness, though there are limited cross-species paradigms available. The 5-choice CPT (5C-CPT) was designed for use in rodents as a cross-species translational paradigm. Here, we evaluate construct validity of a reverse-translated human analog of the 5C-CPT in assessing the neural correlates of vigilance. Functional magnetic resonance imaging during the 5C-CPT was used to examine activation of healthy individuals during target and non-target trials separately. We found activation in brain regions implicated in sustained attention processes including premotor cortex, inferior parietal lobe, basal ganglia, and thalamus during target trials. For non-target trials, we found expected activation in inferior frontal cortex, premotor cortex, presupplementary motor area, and inferior parietal lobe. Results support the construct validity of the 5C-CPT in measuring attentional and inhibitory systems within a single task paradigm enabling the assessment of vigilance across species. This task can be used for powerful parallel human and animal investigations of the biological basis of vigilance deficits in populations with severe mental illness.

Relationship between reaction time, fine motor control, and visual-spatial perception on vigilance and visual-motor tasks in 22q11.2 Deletion Syndrome

22q11.2 Deletion Syndrome (22q11DS) is a common microdeletion disorder associated with mild to moderate intellectual disability and specific neurocognitive deficits, particularly in visual-motor and attentional abilities. Currently there is evidence that the visual-motor profile of 22q11DS is not entirely mediated by intellectual disability and that these individuals have specific deficits in visual-motor integration. However, the extent to which attentional deficits, such as vigilance, influence impairments on visual motor tasks in 22q11DS is unclear. This study examines visual-motor abilities and reaction time using a range of standardised tests in 35 children with 22q11DS, 26 age-matched typically developing (TD) sibling controls and 17 low-IQ community controls. Statistically significant deficits were observed in the 22q11DS group compared to both low-IQ and TD control groups on a timed fine motor control and accuracy task. The 22q11DS group performed significantly better than the low-IQ control group on an untimed drawing task and were equivalent to the TD control group on point accuracy and simple reaction time tests. Results suggest that visual motor deficits in 22q11DS are primarily attributable to deficits in psychomotor speed which becomes apparent when tasks are timed versus untimed. Moreover, the integration of visual and motor information may be intact and, indeed, represent a relative strength in 22q11DS when there are no time constraints imposed. While this may have significant implications for cognitive remediation strategies for children with 22q11DS, the relationship between reaction time, visual reasoning, cognitive complexity, fine motor speed and accuracy, and graphomotor ability on visual-motor tasks is still unclear.

Functional MRI of sustained attention in bipolar mania

We examined sustained attention deficits in bipolar disorder and associated changes in brain activation assessed by functional magnetic resonance imaging (fMRI). We hypothesized that relative to healthy participants, those with mania or mixed mania would (1) exhibit incremental decrements in sustained attention over time, (2) overactivate brain regions required for emotional processing and (3) progressively underactivate attentional regions of prefrontal cortex. Fifty participants with manic/mixed bipolar disorder (BP group) and 34 healthy comparison subjects (HC group) received an fMRI scan while performing a 15-min continuous performance task (CPT). The data were divided into three consecutive 5-min vigilance periods to analyze sustained attention. Composite brain activation maps indicated that both groups activated dorsal and ventral regions of an anterior-limbic network, but the BP group exhibited less activation over time relative to baseline. Consistent with hypotheses 1 and 2, the BP group showed a marginally greater behavioral CPT sustained attention decrement and more bilateral amygdala activation than the HC group, respectively. Instead of differential activation in prefrontal cortex over time, as predicted in hypothesis 3, the BP group progressively decreased activation in subcortical regions of striatum and thalamus relative to the HC group. These results suggest that regional activation decrements in dorsolateral prefrontal cortex accompany sustained attention decrements in both bipolar and healthy individuals. Stable amygdala overactivation across prolonged vigils may interfere with sustained attention and exacerbate attentional deficits in bipolar disorder. Differential striatal and thalamic deactivation in bipolar disorder is interpreted as a loss of amygdala (emotional brain) modulation by the ventrolateral prefrontal-subcortical circuit, which interferes with attentional maintenance.

Antisocial personality and bipolar disorder: interactions in impulsivity and course of illness

Antisocial personality disorder (ASPD) and bipolar disorder are both characterized by impulsive behavior, increased incarceration or arrest, addictive disorders and suicidal behavior. These characteristics appear more severe in the combined disorders. Individuals with ASPD who also have bipolar disorder have higher rates of addictive disorders and suicidal behavior and are more impulsive, as measured by questionnaires or behavioral laboratory tests. Those with bipolar disorder who have ASPD have higher rates of addictive, criminal and suicidal behavior, earlier onset of bipolar disorder with a more recurrent and predominately manic course and increased laboratory-measured, but not questionnaire-rated, impulsivity. These characteristics may result in part from differential impulsivity mechanisms in the two disorders, with bipolar disorder driven more by excessive catecholamine sensitivity and ASPD by deficient serotonergic function.

Working memory and multidimensional schizotypy: dissociable influences of the different dimensions

Compromised working memory is considered a core deficit of schizophrenia and a potential endophenotype for the liability to develop schizophrenia. In keeping with this suggestion, working memory has also been found to be disrupted in people with high levels of schizotypy. However, it is unclear whether this disruption is linked to positive, negative, or disorganized symptoms/characteristics. This issue is the focus of the present investigation. The relationship between multidimensional schizotypy and working memory performance was investigated in 289 participants. Working memory was measured using an n-back task with three conditions; 0-back, 1-back, and 2-back. Covarying for the effect of shared variance between the schizotypy dimensions, we found reduced working memory performance in participants who displayed high levels of positive schizotypy and, to some extent, in participants with low levels of negative schizotypy. The results are discussed in terms of Baddeley's (1986) model of working memory and potential underlying neurological mechanisms.

Interacting mechanisms of impulsivity in bipolar disorder and antisocial personality disorder

BACKGROUND

Bipolar disorder and antisocial personality disorder (ASPD) overlap in clinical characteristics and behavioral consequences. Impulsivity is prominent in both, but there is little information on how specific mechanisms of impulsivity differentiate, bridge, or underlie the disorders.

METHODS

Subjects, all males, were controls (n = 46), bipolar disorder without cluster B personality disorder (n = 21), ASPD without bipolar disorder (n = 50), and bipolar disorder with ASPD (n = 16). Impulsivity measures were the Immediate Memory Task (IMT), a continuous performance test of response inhibition measuring ability to evaluate a stimulus before responding, and the Two-Choice Impulsivity Paradigm (TCIP), a choice between smaller-sooner and larger-later reward. Data were analyzed using general linear models analysis.

RESULTS

Subjects with bipolar disorder had fewer IMT correct detections and slower reaction times than controls. Reaction times were faster with combined diagnoses than in bipolar disorder alone. TCIP responding in either diagnosis alone resembled controls, but was more impulsive in combined disorders. These differences persisted after correction for age and education, which had significant independent effects. In combined ASPD and bipolar disorder, increased reaction speed, impulsive response bias, and reward-delay impulsivity occurred independent of substance-use disorder history.

CONCLUSIONS

Impulsivity was increased in the combined disorders over either disorder alone. Results were consistent with at least partially distinct mechanisms of impulsivity in ASPD and bipolar disorder. Compensatory mechanisms for impulsivity in uncomplicated ASPD or bipolar disorder appear to be compromised or lost when the disorders are combined.

The 5-HTTLPR polymorphism, impulsivity and suicide behavior in euthymic bipolar patients

BACKGROUND

Suicide behavior is very frequent in Bipolar Disorder (BD) and they are both closely associated with impulsivity. Furthermore they are, impulsivity, BD and suicide behavior, associated with serotonergic function, at least partially, under genetic determinism and somewhat associated with the serotonin transporter gene polymorphism, the 5-HTTLPR. We aimed to assess different impulsivity components in BD sub-grouped by suicidal attempt and healthy controls. We hypothesized that the non-planning/cognitive impulsivity, could be more closely associated with suicidal behavior. We further associated 5-HTTLPR genotypes with neuropsychological results to test the hypothesis that this polymorphism is associated with cognitive impulsivity.

METHOD

We assessed 95 euthymic bipolar patients sub-grouped by suicidal attempt history in comparison with 94 healthy controls. All subjects underwent a laboratory assessment of impulsivity (Continuous Performance Test and Iowa Gambling Test). Furthermore the genotyping of 5-HTTLPR was performed in all subjects.

RESULTS

We found that bipolar patients are more impulsive than healthy controls in all impulsivity dimensions we studied. Furthermore bipolar patients with a suicide attempt history have a greater cognitive impulsivity when compared to both bipolar patients without such a history as well when compared to healthy controls. No association was found between 5-HTTLPR genotypes and neuropsychological measures of impulsive behavior.

LIMITATIONS

The sample studied can be considered small and a potentially confounding variable - medication status - was not controlled.

CONCLUSION

A lifetime suicide attempt seems associated with cognitive impulsivity independently of the socio-demographic and clinical variables studied as well with 5-HTTLPR genotype. Further studies in larger samples are necessary.

Classification of first-episode schizophrenia patients and healthy subjects by automated MRI measures of regional brain volume and cortical thickness

BACKGROUND

Although structural magnetic resonance imaging (MRI) studies have repeatedly demonstrated regional brain structural abnormalities in patients with schizophrenia, relatively few MRI-based studies have attempted to distinguish between patients with first-episode schizophrenia and healthy controls.

METHOD

Three-dimensional MR images were acquired from 52 (29 males, 23 females) first-episode schizophrenia patients and 40 (22 males, 18 females) healthy subjects. Multiple brain measures (regional brain volume and cortical thickness) were calculated by a fully automated procedure and were used for group comparison and classification by linear discriminant function analysis.

RESULTS

Schizophrenia patients showed gray matter volume reductions and cortical thinning in various brain regions predominantly in prefrontal and temporal cortices compared with controls. The classifiers obtained from 66 subjects of the first group successfully assigned 26 subjects of the second group with accuracy above 80%.

CONCLUSION

Our results showed that combinations of automated brain measures successfully differentiated first-episode schizophrenia patients from healthy controls. Such neuroimaging approaches may provide objective biological information adjunct to clinical diagnosis of early schizophrenia.

Hemispheric asymmetry in recognition memory: effects of retention level on the recognition of Portuguese words

Early findings from Broca and Wernicke led to the classical view of hemispheric specialization, where the main idea relates to left-hemisphere language capabilities compared to right-hemisphere visual capabilities. Federmeier and Benjamin (2005) have suggested that semantic encoding for verbal information in the right hemisphere can be more effective when memory demands are higher. In light of this, our main goal was to study the effect of retention level of verbal information on hemispheric processes. However, regarding the cross-linguistic differences in orthography and their subsequent effects on word recognition (Frost, Katz, & Bentin, 1987), our intent was also to test prior predictions of Federmeier and Benjamin (2005) for a "shallow" orthography language, where words have a clear correspondence between graphemes and phonemes, as opposed to English, which is a "deep" orthography language. Portuguese concrete nouns were selected. The participants were submitted to a visual half-field word presentation using a continuous recognition memory paradigm. The retention level included 1, 2, 4, 8, 20 or 40 words. Results showed that recognition accuracy was higher for words studied in the right visual field, compared to those studied in the left visual field, when the retention interval included 2, 4, or 20 words. No significant differences were found for the remaining intervals. Further analysis on accuracy data for intermediate retention levels showed that recognition accuracy was higher for the 2 words retention level than for the levels including 4, 8, or 20 words; it was higher for left-hemisphere encoding as well. Our results also indicated that reaction times were slower for left-hemisphere encoding and for the 40 words retention level when compared to that of 20 words. In summary, the current results are in partial agreement with those of Federmeier and Benjamin (2005) and suggest different hemispheric memory strategies for the semantic encoding of verbal information.

Dissociation of acute and chronic intermittent phencyclidine-induced performance deficits in the 5-choice serial reaction time task: influence of clozapine

BACKGROUND

Cognitive deficits are a core feature of schizophrenia that respond minimally to existing drugs. PCP is commonly used to model schizophrenia-like deficits preclinically although different dosing protocols may affect different domains. Here we characterise the acute, and chronic intermittent effects of PCP in the 5-choice serial reaction time task (5-CSRTT) in rats, and assess the effects of clozapine. In a novel approach, we also assess the effects of increased inhibitory load and conduct clinically relevant signal detection analysis (SDA).

MATERIALS AND METHODS

The effects of acute and repeated PCP (2.58 mg/kg) treatment on attentional processes and inhibitory control were assessed during and following the chronic treatment regime in the presence or absence of chronic clozapine (20 mg/kg/day).

RESULTS

Thirty minutes post-PCP injection, there was an increase in anticipatory responding which disappeared after 24 h. Although, acute PCP did not change accuracy of responding or processing speed, repeated PCP revealed delayed deficits in cognitive processing speed which were partly ameliorated by clozapine. Extended inter-trial intervals increased premature responding, while SDA revealed that clozapine modified persistent PCP-induced deficits in lnBeta (a composite measure of risk taking versus caution).

CONCLUSION

Acute NMDA receptor antagonism impairs inhibitory control, whereas repeated treatment produces delayed deficits in cognitive processing speed. The ability of clozapine partially to restore persistent PCP-induced deficits in processing speed and in lnBeta is consistent with clinical findings. This suggests that the enduring effects of repeated PCP treatment, combined with SDA, offers a useful, translational, approach to evaluate novel cognitive enhancers in the 5-CSRTT.

Sustained attention as a potential endophenotype for bipolar disorder

OBJECTIVE

Nowadays, it is accepted that to identify the biological basis of psychiatric illnesses it would be useful to deconstruct them into the most basic manifestations, such as cognitive deficits. The aim of this study was to set attention deficit as a stable vulnerability marker of bipolar disorder.

METHOD

Sustained attention was evaluated by the Continuous Performance Test (DS-CPT) in 143 euthymic bipolar patients and 105 controls. To estimate the influence of clinical profile in attention, patients completed a semi-structured interview.

RESULTS

Bipolar patients showed a deficit in attention during euthymic periods. This disturbance correlated with years of evolution, age of onset and age of first hospitalisation; and was not influenced by other clinical data.

CONCLUSION

Sustained attention may be considered as an endophenotype of the illness.

Frequency of attention deficit in first-episode schizophrenia compared to ADHD

Attention deficit in schizophrenia may be underestimated due to limited sensitivity of attention tests. Comparing the frequency of attention deficits in schizophrenia to attention deficit hyperactivity disorder (ADHD) may solve this problem, since all subjects with ADHD should demonstrate impaired attention. Twenty-seven subjects with schizophrenia were compared to 74 clinical controls with ADHD on tests of focused/divided/sustained attention and impulsivity.

RESULTS

The frequency of impaired attention was equal among subjects with schizophrenia and ADHD-combined (ADHD-C), while ADHD-inattentive (ADHD-I) subjects were more impaired. Half the subjects with schizophrenia had a mild impairment in dual processing. Twenty-one percent showed normal performance on all tests. Fewer subjects with schizophrenia were impulsive/hyperactive, and fewer were impaired in sustained attention compared with the ADHD-C and ADHD-I groups, respectively.

CONCLUSION

Attention tests are not sufficiently sensitive to attention deficits in everyday functioning. Taking this into account, the possibility still remains that a substantial portion of subjects with schizophrenia are not impaired in attention.

Impulsivity across the course of bipolar disorder

OBJECTIVE

To determine whether abnormalities of impulse control persist across the course of bipolar disorder, thereby representing potential state markers and endophenotypes.

METHODS

Impulse control of 108 bipolar I manic or mixed patients was measured on three tasks designed to study response inhibition, ability to delay gratification, and attention; namely, a stop signal task, a delayed reward task, and a continuous performance task, respectively. Barrett Impulsivity Scale (BIS-11) scores were also obtained. Patients were then followed for up to one year and reassessed with the same measures if they developed depression or euthymia. Healthy comparison subjects were also assessed with the same instruments on two occasions to assess measurement stability.

RESULTS

At baseline, bipolar subjects demonstrated significant deficits on all three tasks as compared to healthy subjects, consistent with more impulsive responding in the bipolar manic/mixed group. In general, performance on the three behavioral tasks normalized upon switching to depression or developing euthymia. In contrast, BIS-11 scores were elevated during mania and remained elevated as bipolar subjects developed depression or achieved euthymia.

CONCLUSIONS

Bipolar I disorder patients demonstrate deficits on laboratory tests of various aspects of impulsivity when manic, as compared to healthy subjects, that largely normalize with recovery and switching into depression. However, elevated BIS-11 scores persist across phases of illness. These findings suggest that impulsivity has both affective-state dependent and trait components in bipolar disorder.

Differentiation of first-episode schizophrenia patients from healthy controls using ROI-based multiple structural brain variables

BACKGROUND

Brain morphometric measures from magnetic resonance imaging (MRI) have not been used to discriminate between first-episode patients with schizophrenia and healthy subjects.

METHODS

Magnetic resonance images were acquired from 34 (17 males, 17 females) first-episode schizophrenia patients and 48 (24 males, 24 females) age- and parental socio-economic status-matched healthy subjects. Twenty-nine regions of interest (ROI) were measured on 1-mm-thick coronal slices from the prefrontal and central parts of the brain. Linear discriminant function analysis was conducted using standardized z scores of the volumes of each ROI.

RESULTS

Discriminant function analysis with cross-validation procedures revealed that brain anatomical variables correctly classified 75.6% of male subjects and 82.9% of female subjects, respectively. The results of the volumetric comparisons of each ROI between patients and controls were generally consistent with those of the previous literature.

CONCLUSIONS

To our knowledge, this study provides the first evidence of MRI-based successful classification between first-episode patients with schizophrenia and healthy controls. The potential of these methods for early detection of schizophrenia should be further explored.

Validity of the factor structure of Conners' CPT

OBJECTIVE

A previous factor analysis of the Conners' Continuous Performance Test (CCPT) indicates that the test measures 5 sub-functions of attention, namely focused attention, hyperactivity/impulsivity, sustained attention, vigilance, and change in control. The present study further analyzes the results from Egeland & Kowalik-Gran to test the construct- and criterion-validity of these factors.

METHOD

Construct validity is tested by analyzing whether clinical groups known to be impaired in specified subprocesses actually differ with regard to factor scores. Comparison of CCPT factor scores from 282 individuals with ADHD, schizophrenia, affective disorders, brain injury, language disorders, and normal individuals gives validity to 4 factors, but not to the vigilance factor.

RESULTS

Other tests of controlled attention correlate only with focused attention, thus giving criterion validity to this factor and differential validity to the remaining 4 factors.

CONCLUSION

Grouping scores on the CCPT into 4 or 5 sub-functions of attention may provide the clinician with a tool to differentiate between clinical groups.

Differential brain activation during response inhibition in bipolar and attention-deficit hyperactivity disorders

AIM

To identify differential patterns of brain activation between adolescents with bipolar disorder and adolescents with attention-deficit hyperactivity disorder (ADHD) to better understand the neurophysiology of both disorders. We hypothesized that subjects with ADHD would show altered activation in brain regions involved in executive and sustained attention. In contrast, we hypothesized that bipolar subjects would show altered brain activation in regions responsible for emotionally homeostasis, including the striatum and amygdala.

METHODS

Functional magnetic resonance imaging was performed during a continuous performance task with a response inhibition component in 11 adolescents with bipolar disorder during a manic episode, 10 adolescents with ADHD, and 13 healthy adolescents.

RESULTS

There were no differences in behavioural performance among the three groups. Compared with bipolar subjects, subjects with ADHD showed increased activation in the superior temporal lobe during successful response inhibition. Although bipolar subjects did not show activation differences in the striatum or amygdala compared with ADHD subjects, increased left parahippocampal activation in the bipolar group was associated with increased manic symptoms.

CONCLUSIONS

The patterns of brain activation observed in the current study support divergent patterns of neurophysiological dysfunction in individuals with bipolar disorder as compared with those with ADHD. Therefore, the impulsive behaviour seen in both disorders may be the consequence of dysfunction in different brain regions, and further research may help identify neurobiological markers that are specific to each condition.

Severity of bipolar disorder is associated with impairment of response inhibition

BACKGROUND

Pathological impulsivity in bipolar disorder could be related to deficiencies in mechanisms involved in attention or response inhibition. We investigated these mechanisms in subjects with bipolar disorder and examined relationships to severity of course of illness, use of medication, affective state, age, education, and gender. We measured two complementary aspects of response inhibition: attention-based and reward-based.

METHODS

Subjects with bipolar disorder (n=112) and healthy controls (n=71) were recruited from the community. Diagnoses were rendered using the SCID for DSMIV. Impulsivity-related measures included the Immediate Memory Task (IMT), a form of the Continuous Performance Task, and the Single Key Impulsivity Paradigm (SKIP), an operant procedure measuring ability to delay responding for a reward.

RESULTS

Subjects with bipolar disorder had fewer correct detections (Effect Size (ES)=0.5), prolonged reaction times (ES=0.88), and decreased discriminability (ES=0.57) on the IMT compared to controls. History of frequent episodes, substance use disorders, or suicide attempts predicted faster reaction times, especially to a commission error. Subjects with bipolar disorder who also met criteria for an Axis II disorder had fewer correct detections, more commission errors relative to correct detections, and poorer discriminability on the IMT than other subjects with bipolar disorder. Subjects with bipolar disorder made more responses on the SKIP than did controls (ES=0.5), with a shorter maximum delay (ES=0.62), consistent with inability to delay reward. Probit analysis showed that faster reaction time to a commission error on the IMT was associated with history of substance use disorder, suicide attempt, or many previous episodes. Effects of medication or affective state did not account for these differences.

DISCUSSION

Bipolar disorder was associated with impairment in attention and response inhibition, encompassing impaired inhibition of rapid responses and an inability to delay reward, and resulting in impulsivity. Response inhibition mechanisms are impaired further in subjects with more severe complications of illness.

Characterizing impulsivity in mania

OBJECTIVE

To determine whether specific aspects of impulsivity (response disinhibition, inability to delay gratification, inattention) differ between healthy and bipolar manic subjects, and whether these aspects of impulsivity were associated with each other and severity of affective symptoms.

METHODS

Performance of 70 bipolar I manic or mixed patients was compared to that of 34 healthy subjects on three tasks specifically designed to study response inhibition, ability to delay gratification, and attention; namely, a stop signal task, a delayed reward task, and a continuous performance task, respectively. Correlations among tasks and with symptom ratings were also performed.

RESULTS

Bipolar subjects demonstrated significant deficits on all three tasks as compared to healthy subjects. Performance on the three tasks was largely independent. Task performance was not significantly associated with the severity of affective symptom ratings. However, measures of response inhibition and attention were sensitive to medication effects. Differences in the delayed reward task were independent of medication effects or symptom ratings. During the delayed reward task, although bipolar patients made their choices more slowly than healthy subjects, they were significantly more likely to choose a smaller, but more quickly obtained reward. Moreover, performance on this task was not associated with performance on the other impulsivity measures. Manic patients showed more impulsive responding than mixed patients.

CONCLUSIONS

Bipolar I manic patients demonstrate deficits on tests of various aspects of impulsivity as compared to healthy subjects. Some of these differences between groups may be mediated by medication effects. Findings suggested that inability to delay gratification (i.e., delayed reward task) was not simply a result of the speed of decision making or inattention, but rather that it reflected differences between bipolar and healthy subjects in the valuation of reward relative to delay.

Humour experience in schizophrenia: relationship with executive dysfunction and psychosocial impairment

BACKGROUND

The ability to appreciate humour is essential to successful human interactions. In this study, we hypothesized that individuals with schizophrenia would have diminished ability to recognize and appreciate humour. The relationship between humour experience and clinical symptoms, cognitive and social functioning was examined.

METHOD

Thirty patients with a DSM-IV diagnosis of schizophrenia were compared with 30 age-, gender-, IQ- and ethnicity-matched healthy controls. Humour recognition was measured by identification of humorous moments in four silent slapstick comedy film clips and calculated as d-prime (d') according to signal detection theory. Humour appreciation was measured by self-report mood state and funniness ratings. Patients were assessed for clinical symptoms, theory of mind ability, executive function [using the Wisconsin Card Sorting Test (WCST)] and social functioning [using the Life Skills Profile (LSP)].

RESULTS

Patient and control groups did not differ in the funniness ratings they attributed to the video clips. Patients with schizophrenia had a lower d' (humour) compared to the controls, after controlling for (1) the performance of a baseline recognition task with a non-humorous video clip and (2) severity of depressive symptoms. In patients, d' (humour) had significant negative correlation with delusion and depression scores, the perseverative error score of the WCST and the total scores of the LSP.

CONCLUSIONS

Compared with controls, patients with schizophrenia were less sensitive at detecting humour but similarly able to appreciate humour. The degree of humour recognition difficulty may be associated with the extent of executive dysfunction and thus contribute to the psychosocial impairment in patients with schizophrenia.

Stimulating the development of drug treatments to improve cognition in schizophrenia

Cognitive impairment in schizophrenia is a core feature of the illness (i.e., not a result of clinical symptoms or drug treatments) that is related to the daily functioning of patients. Because schizophrenia is associated with poor community functioning, there is considerable interest in finding treatments to improve cognition in schizophrenia in the hopes that such improvement will yield functional benefits. Before the U.S. Food and Drug Administration could consider granting approval to any new drug for improving cognition in schizophrenia, it was first necessary to achieve consensus on the measurements and methods that would be used in clinical trials, as well as neuropharmacological targets. The U.S. National Institute of Mental Health launched an initiative to help address these obstacles to drug approval (MATRICS). This initiative has generated several additional follow-up initiatives including a clinical trial network and consensus projects for other clinical targets, such as negative symptoms. This review describes how an area that was primarily of academic interest (cognition in schizophrenia) became a focus of public health concerns and drug-development policy.

A cognitive vulnerability-stress perspective on bipolar spectrum disorders in a normative adolescent brain, cognitive, and emotional development context

Why is adolescence an "age of risk" for onset of bipolar spectrum disorders? We discuss three clinical phenomena of bipolar disorder associated with adolescence (adolescent age of onset, gender differences, and specific symptom presentation) that provide the point of departure for this article. We present the cognitive vulnerability-transactional stress model of unipolar depression, evidence for this model, and its extension to bipolar spectrum disorders. Next, we review evidence that life events, cognitive vulnerability, the cognitive vulnerability-stress combination, and certain developmental experiences (poor parenting and maltreatment) featured in the cognitive vulnerability-stress model play a role in the onset and course of bipolar disorders. We then discuss how an application of the cognitive vulnerability-stress model can explain the adolescent age of onset, gender differences, and adolescent phenomenology of bipolar disorder. Finally, we further elaborate the cognitive vulnerability-stress model by embedding it in the contexts of normative adolescent cognitive (executive functioning) and brain development, normative adolescent development of the stress-emotion system, and genetic vulnerability. We suggest that increased brain maturation and accompanying increases in executive functioning along with augmented neural and behavioral stress-sensitivity during adolescence combine with the cognitive vulnerability-stress model to explain the high-risk period for onset of bipolar disorder, gender differences, and unique features of symptom presentation during adolescence.

Response selection in schizophrenia

Schizophrenia patients tend to have longer and more variable latencies of response than healthy control subjects. However, the distributions of data from the two groups overlap to a large extent. Therefore, we investigated (1) whether the process of response selection in schizophrenia patients is like that of slow control subjects or has different properties, and (2) whether the intra-individual variability of schizophrenia patients is intrinsically greater than that of control subjects or reflects their longer mean latency. To answer these questions we tested schizophrenia patients and healthy control subjects in a choice reaction time (RT) task with 2-choice and 4-choice conditions. We analyzed how mean RT in the 2-choice condition predicted mean RT in the 4-choice condition and found that the relation was significantly different between the two groups. In contrast, the intra-individual variability of RT was related to mean RT in the same way for schizophrenia patients and control subjects. These results indicate that the response selection process of schizophrenia patients was not simply a slower version of the same process engaged by control subjects, but it was a selection process with different dynamic properties. In contrast, schizophrenia patients did not have a greater intrinsic variability than control subjects. Furthermore, we found that the difference Deltat between RT measured in the 4-choice condition and RT predicted for the control group in the same condition could be used to discriminate effectively patients and control subjects. However, there was no significant association between Deltat and clinical variables. These results suggest that Deltat could reflect a trait impairment of schizophrenia independent from symptom profile. Finally, we suggest that the impairment of the process of selection of the motor response in schizophrenia reflects the alteration of the time-dependent patterns of neural activity that result from anomalies in the connectivity of the brain areas engaged for the selection of the motor response.

Reaction time of the Continuous Performance Test is an endophenotypic marker for schizophrenia: a study of first-episode neuroleptic-naive schizophrenia, their non-psychotic first-degree relatives and healthy population controls

Sustained attention has been proposed as an endophenotype of schizophrenia, and consequently may be useful as a quantitative trait in genetic studies. In the present study, we used the continuous performance test (CPT) to measure sustained attention in 112 first-episode and neuroleptic-naive schizophrenic patients, 296 of their non-psychotic first-degree relatives, and 452 normal controls. Compared with controls, probands with schizophrenia showed worse performance on all measures of CPT. Parents, siblings and offspring of probands were also impaired on 'hit reaction time', an index of psychomotor processing speed of the correct response. Hit reaction time was also independent of the acute clinical features of the disease, indicating it is a trait rather than a state marker. Our findings supported the use of the hit reaction time measure of the CPT as an endophenotype marker for schizophrenia.

Preliminary evidence of differential relations between prefrontal cortex metabolism and sustained attention in depressed adults with bipolar disorder and healthy controls

OBJECTIVES

To assess the relations between sustained attention as assessed by the Continuous Performance Test (CPT) and subgenual and dorsolateral prefrontal cortex metabolism in depressed patients with bipolar disorders and healthy controls.

DESIGN

Cross-sectional case-control design.

METHODS

Cerebral metabolic rates were assessed with 18F-fluoro-deoxyglucose and positron emission tomography (PET) in the regions of interest defined on co-registered structural magnetic resonance images in eight medication-free, depressed bipolar disorder patients and 27 healthy control participants. PET scans were obtained in a resting state and the CPT was administered within 1 week of the PET scan.

RESULTS

Although there were no statistically significant differences in performance on the CPT or in cerebral metabolism between the two groups, our analyses revealed differential relations between the CPT and metabolism across the groups. Decreased subgenual prefrontal metabolism was associated with slower hit rate reaction time and more omission errors in the bipolar group, but not the control group. Decreased dorsolateral prefrontal metabolism in the bipolar group, but not the control group, was associated with more commission errors.

CONCLUSIONS

This study extends previous neuroimaging findings of structural and functional relevance of the prefrontal region with attention to include depressed states in bipolar disorder. The results are consistent with interpretations that decreased prefrontal activity may represent failure to activate some areas of inhibitory control. Decreasing subgenual prefrontal cortex metabolism appears to relate to decreased attention whereas the decreased dorsolateral prefrontal cortex metabolism relates more to decreased inhibitory control.

Neurocognition as a stable endophenotype in bipolar disorder and schizophrenia

Linkage and association studies have paid increasing attention to neurocognition as a putative endophenotype. However, there exists little documentation of its trait stability in schizophrenia or bipolar disorder. Our aim was to determine the longitudinal stability of neurocognitive performance in bipolar versus schizophrenia probands. We administered a neurocognitive battery at two time points, approximately 5 years apart, in 16 schizophrenia and 16 bipolar disorder age-matched subjects. There were no significant changes over time on variables including education, estimated IQ, depression, psychosis, global functioning, or medication status. Schizophrenia subjects showed significant deterioration in one measure of executive functioning but no significant changes in seven of eight other domains. Bipolar patients showed stability over time in attentional measures but greater variability in other domains. These preliminary findings suggest that neurocognitive domains appear longitudinally stable across broad domains in schizophrenia. In contrast, stable functioning may be more limited to attentional domains in bipolar disorder.

When euthymia is just not good enough: the neuropsychology of bipolar disorder

Bipolar disorder (BD) is a debilitating psychiatric illness that is uniquely characterized by switching between psychopathologically contrasting phases of mania and depression, often with intervening periods of euthymia. However, these periods of apparent clinical recovery (euthymia) are marked by subtle social, occupational, and cognitive impairments, profiled by recent neuropsychological investigations. Determining the cognitive changes across these three phases may help differentiate the disruptions that are mood state-dependent from those associated with underlying pathology. This article therefore critically reviews the reported neuropsychological impairments in BD and the methodological limitations facing such research. Integration of the available evidence, principally from the field of neuropsychology, when synthesized, implicates the prefrontal cortex in the etiopathogenesis of BD and posits cortical-subcortical-limbic disruption in recovered euthymic patients that manifests as cognitive dysfunction.

Evidence for unaltered brain electrical topography during prefrontal response control in cycloid psychoses

OBJECTIVE

Prefrontal structures such as the anterior cingulate cortex (ACC) play a decisive role in processes of action monitoring and response control, functions often impaired in schizophrenia. Patients with cycloid psychoses exhibit some characteristic neurophysiological features not indicative of the cerebral hypofrontality observed in schizophrenia. This study aimed at examining if cycloid psychoses-unlike schizophrenias-involve a normal brain-electrical topography during a task demanding prefrontal response control.

METHODS

Thirty-seven patients with cycloid psychoses and 37 healthy controls were investigated electrophysiologically while performing a Continuous Performance Test (CPT). Topographical analyses were conducted to individually quantify the Nogo-anteriorisation (NGA) as a neurophysiological index of prefrontal response control.

RESULTS

The patients exhibited an unaltered topography with a mean NGA not significantly different from the controls. They did, however, differ from the control group regarding their Global Field Power (GFP), with a significantly reduced GFP (p<0.001) and decreased latencies (p<0.01) during Nogo trials. On a behavioral level, patients exhibited prolonged reaction times and an increased rate of omission errors.

CONCLUSIONS

The investigated patients showed an activation of specific (presumably frontal) brain areas during Nogo trials, resulting in a frontalisation of the brain-electrical field comparable to the control group. However, the strength of this activation was apparently reduced. The patients' unaltered topographical pattern contrasts with previous findings in schizophrenic patients and supports the hypothesis that cycloid psychoses entail less severe prefrontal deficits than schizophrenias, which might be an indication of different biological backgrounds for both groups of endogenous psychoses.

Attention deficits in bipolar disorder: a comparison based on the Continuous Performance Test

Although attentional deficits measured by Continuous Performance Tests (CPTs) have been observed in patients with bipolar disorder, their relationship with clinical state is not well understood. The identical pairs Continuous Performance Test (CPT-IP) shows particular promise as a measure sensitive to trait abnormalities in attentional function. In this study, the CPT-IP was administered to 27 patients with bipolar disorder (22 type I, 5 type II) and 25 demographically matched healthy comparison subjects, in order to assess the presence and nature of attentional deficits as a function of mood symptoms. Results showed significantly impaired CPT performance in bipolar patients compared with healthy subjects. Patients made fewer hits (p < 0.01), were slower to respond (p < 0.007), and had poorer discrimination (p < 0.05) and bias (p < 0.006) than comparison subjects. Severity of mania and depression was not correlated with any of the CPT measures. Our findings suggest that attentional dysfunction may be a trait deficit associated with bipolar illness. However, within-subjects longitudinal studies examining fluctuations in performance over time are needed.

Processing efficiency and sustained attention in bipolar disorder

We hypothesized that patterns of sustained attention performance in bipolar disorder were consistent with processing efficiency theory--a theory of the relationship between central processing capacity and performance. We predicted (1) sustained attention deficits during mania because symptoms interfere with limited-capacity executive control processes resulting in decreased performance effectiveness; and (2) decreased processing efficiency during euthymia, as indicated by speed/accuracy tradeoffs, consistent with a stable phenotypic abnormality. Twenty-five manic bipolar, 23 euthymic bipolar, and 28 healthy comparison participants were compared on a continuous performance task and administered symptom-rating scales. The manic group was significantly impaired on overall perceptual sensitivity and demonstrated a significant linear decrease in performance over time, consistent with impaired sustained attention. The euthymic group evidenced significantly slower overall hit reaction time (RT), but when RT was controlled they performed similarly to the healthy group over time. Two discriminant functions combined to separate the groups on manic symptom severity and on-task effort/strategy use. These findings are consistent with processing efficiency theory. They suggest that euthymic patients sustain attention through effortful control at the expense of processing efficiency, while acute mania reduces the capacity for control and impairs sustained attention. Problems with processing efficiency are viewed as trait characteristics of bipolar disorder that may be overlooked by traditional error-based assessments.

Parametric neurocognitive task design: a pilot study of sustained attention in adolescents with bipolar disorder

BACKGROUND

Disruption in attention is one of the core features of bipolar disorder (BP). Therefore, neurocognitive paradigms assessing brain function in response to tasks of increasing attentional difficulty may be useful to clarify the neurophysiology of bipolar disorder. The aim of this study was to obtain pilot performance data using a parametric task of sustained attention that might be useful as an experimental paradigm for future functional neuroimaging studies. We hypothesized that task performance would worsen as task difficulty increased in manic and euthymic bipolar and healthy subjects. Additionally, we hypothesized that the groups would exhibit a similar decline in task performance as level of task difficulty increased and that within each level of task difficulty there would be similar performance among groups.

METHODS

A novel parametric Continuous Performance Task-Identical Pairs (CPT-IP) version was administered to manic (N=10) and euthymic (N=10) adolescents with bipolar disorder and healthy controls (N=10).

RESULTS

There were no statistically significant group differences in task performance as measured by discriminability, percent correct, false positive hits, and reaction time. However, within each group, performance on all measures worsened with increased attentional difficulty (p<0.0001). There were no statistically significant task difficulty by group interactions. Furthermore, medication exposure and comorbid attention-deficit hyperactivity disorder were not associated with most measures of task performance. However, BP subjects who were treated with medications had slower task performance compared with BP subjects who were unmedicated.

LIMITATIONS

Larger studies examining the effects of specific medication classes on task performance are necessary.

CONCLUSIONS

The results of this pilot study suggest that manic and euthymic BP patients do not exhibit attentional dysfunction as compared to healthy adolescents using a novel parametric version of the CPT-IP. Furthermore, our parametric CPT-IP version may be useful as a novel parametric neurocognitive paradigm for future functional neuroimaging studies of bipolar adolescents.

Approaching a consensus cognitive battery for clinical trials in schizophrenia: the NIMH-MATRICS conference to select cognitive domains and test criteria

To stimulate the development of new drugs for the cognitive deficits of schizophrenia, the National Institute of Mental Health (NIMH) established the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. This article presents an overview of decisions from the first MATRICS consensus conference. The goals of the meeting were to 1) identify the cognitive domains that should be represented in a consensus cognitive battery and 2) prioritize key criteria for selection of tests for the battery. Seven cognitive domains were selected based on a review of the literature and input from experts: working memory, attention/vigilance, verbal learning and memory, visual learning and memory, reasoning and problem solving, speed of processing, and social cognition. Based on discussions at this meeting, five criteria were considered essential for test selection: good test-retest reliability, high utility as a repeated measure, relationship to functional outcome, potential response to pharmacologic agents, and practicality/tolerability. The results from this meeting constitute the initial steps for reaching a consensus cognitive battery for clinical trials in schizophrenia.

Verbal memory in mania: effects of clinical state and task requirements

OBJECTIVES

Manic patients exhibit impaired verbal learning and memory, particularly following longstanding illness. However, it is unclear whether recognition and recall performance are differentially influenced by a manic mood state.

METHODS

To examine this issue, we administered the California Verbal Learning Test and symptom-rating scales to inpatients with pure or mixed mania, euthymic outpatients, and healthy comparison subjects.

RESULTS

An overall performance difference was identified between groups. Manic and euthymic patients performed more poorly than healthy subjects on recall. However, manic patients performed more poorly than euthymic patients and healthy subjects on recognition.

CONCLUSIONS

These results suggest that verbal retrieval deficits are stable vulnerability indicators in bipolar disorder, whereas verbal encoding deficits are manic episode indicators. The known subcortical dysfunction in this disorder may produce stable retrieval deficits while acute mood symptoms attenuate encoding during affective episodes only.

The schizophrenia phenotype in 22q11 deletion syndrome

OBJECTIVE

This study investigated the schizophrenia phenotype in 24 subjects with 22q11 deletion syndrome (22qDS) and schizophrenia (22qDS-schizophrenia), a rare but relatively homogenous genetic subtype of schizophrenia associated with a microdeletion on chromosome 22. Individuals with 22qDS are at genetically high risk for schizophrenia.

METHOD

Standard measures of signs, symptoms, and course of schizophrenia were assessed in 16 adults with 22qDS-schizophrenia who did not meet criteria for mental retardation and in 46 adults with schizophrenia without evidence of 22qDS from a community familial sample.

RESULTS

There were no significant differences in age at onset, lifetime or cross-sectional core positive and negative schizophrenic symptoms, or global functioning between the two groups of patients with schizophrenia. Patients with 22qDS-schizophrenia had higher excitement subscale scores and less lifetime substance use than the comparison patients with schizophrenia, but no significant differences in anxiety-depression symptom severity were found between the groups.

CONCLUSIONS

These findings indicate that the core clinical schizophrenia phenotype would not distinguish individuals with a 22qDS subtype from those with schizophrenia who did not have the 22qDS subtype. The results provide further support for the utility of 22qDS-schizophrenia as a neurodevelopmental model of schizophrenia as well as support for prospective studies of individuals with 22qDS to help identify precursors of schizophrenia.

Researching the pathophysiology of pediatric bipolar disorder

We suggest that the core feature of bipolar disorder (BPD) is marked state fluctuations. The pathophysiology of switches into depressed, irritable, and extreme positive valence states requires study, with the latter deserving particular focus because it represents a pathognomonic feature of BPD in both adults and children. Hypotheses regarding the pathophysiology of pediatric BPD must account for these marked state fluctuations as well as for specific developmental aspects of the illness. These developmental aspects include marked irritability (in addition to euphoria and depression) and very rapid cycles, along with high rates of attention-deficit/hyperactivity disorder. We review research on neural mechanisms underlying positive valence states and state regulation, focusing on those data relevant to BPD and to development. Researchers are beginning to explore the response of manic patients and control subjects to positive affective stimuli, and considerable research in both nonhuman primates and humans has focused on the cortico-limbic-striatal circuits mediating responses to rewarding stimuli. In control subjects, positive affect affects cognition, and data indicate that prefrontal electroencephalogram asymmetry may differ between control subjects with consistently positive affect and those with more negative affect; however, this latter generalization may not apply to adolescents. With regard to the pathophysiology of state switching in pediatric BPD, data in control subjects indicating that attention regulation plays a role in emotion regulation may be germane. In addition, research detailing physiologic and psychological responses to negative emotional stimuli in bipolar patients and control subjects may increase our understanding of the mechanisms underlying both irritability and rapid cycling seen in children with BPD. Potential foci for research on the pathophysiology of pediatric BPD include reactivity to standardized positive and negative emotional stimuli, and the interaction between emotion regulation and attentional processes.