Changes in neuronal activation in patients with bipolar disorder during performance of a working memory task

Altered affective, executive and sensorimotor resting state networks in patients with pediatric mania

BACKGROUND

The aim of the present study was to map the pathophysiology of resting state functional connectivity accompanying structural and functional abnormalities in children with bipolar disorder.

METHODS

Children with bipolar disorder and demographically matched healthy controls underwent resting-state functional magnetic resonance imaging. A model-free independent component analysis was performed to identify intrinsically interconnected networks.

RESULTS

We included 34 children with bipolar disorder and 40 controls in our analysis. Three distinct resting state networks corresponding to affective, executive and sensorimotor functions emerged as being significantly different between the pediatric bipolar disorder (PBD) and control groups. All 3 networks showed hyperconnectivity in the PBD relative to the control group. Specifically, the connectivity of the dorsal anterior cingulate cortex (ACC) differentiated the PBD from the control group in both the affective and the executive networks. Exploratory analysis suggests that greater connectivity of the right amygdala within the affective network is associated with better executive function in children with bipolar disorder, but not in controls.

LIMITATIONS

Unique clinical characteristics of the study sample allowed us to evaluate the pathophysiology of resting state connectivity at an early state of PBD, which led to the lack of generalizability in terms of comorbid disorders existing in a typical PBD population.

CONCLUSION

Abnormally engaged resting state affective, executive and sensorimotor networks observed in children with bipolar disorder may reflect a biological context in which abnormal task-based brain activity can occur. Dual engagement of the dorsal ACC in affective and executive networks supports the neuroanatomical interface of these networks, and the amygdala's engagement in moderating executive function illustrates the intricate interplay of these neural operations at rest.

Bipolar depressed patients show both failure to activate and failure to de-activate during performance of a working memory task

BACKGROUND

Bipolar depression has been found to be associated with changes in prefrontal cortex activity during performance of cognitive tasks. However, the role of task-related de-activations has been little investigated.

METHOD

Forty-one bipolar depressed patients and 41 matched normal controls underwent fMRI scanning while performing baseline, 1-back and 2-back versions of the n-back task. Linear models were used to obtain maps of within-group activations and areas of differential activation between the groups.

RESULTS

The bipolar depressed patients showed reduced activation in the dorsolateral prefrontal cortex (DLPFC) bilaterally and several other regions. After controlling for differences in task performance only differences in the DLPFC and cerebellum remained. Left DLPFC activation was inversely correlated with Hamilton and MADRS scores. The patients showed failure to de-activate in the medial prefrontal cortex, an area corresponding to the anterior medial node of the default mode network.

LIMITATIONS

To confirm default mode network dysfunction demonstration of resting-state connectivity abnormalities would also be required. The study was carried out on treated patients, and did not assess for presence of depressive symptoms in the healthy controls.

CONCLUSIONS

Both prefrontal cortical and default mode network dysfunction appear to characterise bipolar depression. The former, but not the latter, is associated with symptom severity.

Altered regional homogeneity in pediatric bipolar disorder during manic state: a resting-state fMRI study

Pediatric bipolar disorder (PBD) is a severely debilitating illness, which is characterized by episodes of mania and depression separated by periods of remission. Previous fMRI studies investigating PBD were mainly task-related. However, little is known about the abnormalities in PBD, especially during resting state. Resting state brain activity measured by fMRI might help to explore neurobiological biomarkers of the disorder.

METHODS

Regional homogeneity (ReHo) was examined with resting-state fMRI (RS-fMRI) on 15 patients with PBD in manic state, with 15 age-and sex-matched healthy youth subjects as controls.

RESULTS

Compared with the healthy controls, the patients with PBD showed altered ReHo in the cortical and subcortical structures. The ReHo measurement of the PBD group was negatively correlated with the score of Young Mania Rating Scale (YMRS) in the superior frontal gyrus. Positive correlations between the ReHo measurement and the score of YMRS were found in the hippocampus and the anterior cingulate cortex in the PBD group.

CONCLUSIONS

Altered regional brain activity is present in patients with PBD during manic state. This study presents new evidence for abnormal ventral-affective and dorsal-cognitive circuits in PBD during resting state and may add fresh insights into the pathophysiological mechanisms underlying PBD.

Altered regional homogeneity in pediatric bipolar disorder during manic state: a resting-state fMRI study

Pediatric bipolar disorder (PBD) is a severely debilitating illness, which is characterized by episodes of mania and depression separated by periods of remission. Previous fMRI studies investigating PBD were mainly task-related. However, little is known about the abnormalities in PBD, especially during resting state. Resting state brain activity measured by fMRI might help to explore neurobiological biomarkers of the disorder.

METHODS

Regional homogeneity (ReHo) was examined with resting-state fMRI (RS-fMRI) on 15 patients with PBD in manic state, with 15 age-and sex-matched healthy youth subjects as controls.

RESULTS

Compared with the healthy controls, the patients with PBD showed altered ReHo in the cortical and subcortical structures. The ReHo measurement of the PBD group was negatively correlated with the score of Young Mania Rating Scale (YMRS) in the superior frontal gyrus. Positive correlations between the ReHo measurement and the score of YMRS were found in the hippocampus and the anterior cingulate cortex in the PBD group.

CONCLUSIONS

Altered regional brain activity is present in patients with PBD during manic state. This study presents new evidence for abnormal ventral-affective and dorsal-cognitive circuits in PBD during resting state and may add fresh insights into the pathophysiological mechanisms underlying PBD.

Frontopolar cortical inefficiency may underpin reward and working memory dysfunction in bipolar disorder

OBJECTIVES

Emotional dysregulation in bipolar disorder is thought to arise from dysfunction within prefrontal cortical regions involved in cognitive control coupled with increased or aberrant activation within regions engaged in emotional processing. The aim of this study was to determine the common and distinct patterns of functional brain abnormalities during reward and working memory processing in patients with bipolar disorder.

METHODS

Participants were 36 euthymic bipolar disorder patients and 37 healthy comparison subjects matched for age, sex and IQ. Functional magnetic resonance imaging (fMRI) was conducted during the Iowa Gambling Task (IGT) and the n-back working memory task.

RESULTS

During both tasks, patients with bipolar disorder demonstrated a pattern of inefficient engagement within the ventral frontopolar prefrontal cortex with evidence of segregation along the medial-lateral dimension for reward and working memory processing, respectively. Moreover, patients also showed greater activation in the anterior cingulate cortex during the Iowa Gambling Task and in the insula during the n-back task.

CONCLUSIONS

Our data implicate ventral frontopolar dysfunction as a core abnormality underpinning bipolar disorder and confirm that overactivation in regions involved in emotional arousal is present even in tasks that do not typically engage emotional systems.

Differential relations between fronto-limbic metabolism and executive function in patients with remitted bipolar I and bipolar II disorder

OBJECTIVES

The aim of this study was to investigate the relationship between resting brain glucose metabolism and cognitive profiles in patients with remitted bipolar I disorder (BD-I) and bipolar II disorder (BD-II). We hypothesized that BD-I patients (compared to BD-II patients) would perform worse on tests of cognitive function because of abnormal metabolism in the prefrontal cortex and other mood-related brain areas.

METHODS

Thirty-four patients with remitted bipolar disorder (BD) (BD-I = 17, BD-II = 17) under treatment and 17 well-matched healthy controls received both fluorodeoxyglucose ((18) F-FDG) positron emission tomography (PET) and neuropsychological tests of attention, memory, and executive function.

RESULTS

Clinical features in patients with BD-I and BD-II were comparable. Executive function, as indicated by performance on the Wisconsin Card Sorting Test, was significantly worse (i.e., higher percentage of errors, lower percentage of conceptual level responses, and fewer categories completed) in BD-I patients than in BD-II patients and healthy subjects. No difference in attention and memory tests was found among these three groups. Brain PET analysis showed that BD-I patients (compared to BD-II patients) had significantly lower glucose uptake in the bilateral anterior cingulum, insula, striatum, and part of the prefrontal cortex, and higher glucose uptake in the left parahippocampus. Further analyses revealed significant correlations between poor executive function and abnormal glucose uptake in other brain areas in BD-I patients.

CONCLUSIONS

There are neurobiological differences between subtypes of BD. BD-I is associated with more impaired fronto-limbic circuitry, which might account for reduced executive function in BD-I patients during remission.

Overlapping prefrontal systems involved in cognitive and emotional processing in euthymic bipolar disorder and following sleep deprivation: a review of functional neuroimaging studies

Prefrontal cortex (PFC) mediated cognitive and emotional processing deficits in bipolar disorder lead to functional limitations even during periods of mood stability. Alterations of sleep and circadian functioning are well-documented in bipolar disorder, but there is little research directly examining the mechanistic role of sleep and/or circadian rhythms in the observed cognitive and emotional processing deficits. We systematically review the cognitive and emotional processing deficits reliant upon PFC functioning of euthymic patients with bipolar disorder and in healthy individuals deprived of sleep. The evidence from two parallel lines of investigation suggests that sleep and circadian rhythms may be involved in the cognitive and emotional processing deficits seen in bipolar disorder through overlapping neurobiological systems. We discuss current models of bipolar highlighting the PFC-limbic connections and discuss inclusion of sleep-related mechanisms. Sleep and circadian dysfunction is a core feature of bipolar disorder and models of neurobiological abnormalities should incorporate chronobiological measures. Further research into the role of sleep and circadian rhythms in cognition and emotional processing in bipolar disorder is warranted.

Mindfulness-based stress reduction, mindfulness-based cognitive therapy, and Zen meditation for depression, anxiety, pain, and psychological distress

Mindfulness has been described as a practice of learning to focus attention on moment-bymoment experience with an attitude of curiosity, openness, and acceptance. Mindfulness practices have become increasingly popular as complementary therapeutic strategies for a variety of medical and psychiatric conditions. This paper provides an overview of three mindfulness interventions that have demonstrated effectiveness for psychiatric symptoms and/or pain. The goal of this review is to provide a synopsis that practicing clinicians can use as a clinical reference concerning Zen meditation, mindfulness-based stress reduction (MBSR), and mindfulness-based cognitive therapy (MBCT). All three approaches originated from Buddhist spiritual practices, but only Zen is an actual Buddhist tradition. MBSR and MBCT are secular, clinically based methods that employ manuals and standardized techniques. Studies indicate that MBSR and MBCT have broad-spectrum antidepressant and antianxiety effects and decrease general psychological distress. MBCT is strongly recommended as an adjunctive treatment for unipolar depression. The evidence suggests that both MBSR and MBCT have efficacy as adjunctive interventions for anxiety symptoms. MBSR is beneficial for general psychological health and stress management in those with medical and psychiatric illness as well as in healthy individuals. Finally, MBSR and Zen meditation have a role in pain management.

The functional neuroanatomy of bipolar disorder: a consensus model

OBJECTIVES

Functional neuroimaging methods have proliferated in recent years, such that functional magnetic resonance imaging, in particular, is now widely used to study bipolar disorder. However, discrepant findings are common. A workgroup was organized by the Department of Psychiatry, University of Cincinnati (Cincinnati, OH, USA) to develop a consensus functional neuroanatomic model of bipolar I disorder based upon the participants' work as well as that of others.

METHODS

Representatives from several leading bipolar disorder neuroimaging groups were organized to present an overview of their areas of expertise as well as focused reviews of existing data. The workgroup then developed a consensus model of the functional neuroanatomy of bipolar disorder based upon these data.

RESULTS

Among the participants, a general consensus emerged that bipolar I disorder arises from abnormalities in the structure and function of key emotional control networks in the human brain. Namely, disruption in early development (e.g., white matter connectivity and prefrontal pruning) within brain networks that modulate emotional behavior leads to decreased connectivity among ventral prefrontal networks and limbic brain regions, especially the amygdala. This developmental failure to establish healthy ventral prefrontal-limbic modulation underlies the onset of mania and ultimately, with progressive changes throughout these networks over time and with affective episodes, a bipolar course of illness.

CONCLUSIONS

This model provides a potential substrate to guide future investigations and areas needing additional focus are identified.

Trait and state corticostriatal dysfunction in bipolar disorder during emotional face processing

OBJECTIVES

Convergent evidence supports limbic, anterior paralimbic, and prefrontal cortex (PFC) abnormalities in emotional processing in bipolar disorder (BD) and suggests that some abnormalities are mood-state dependent and others persist into euthymia. However, few studies have assessed elevated, depressed, and euthymic mood states while individuals processed emotional stimuli of varying valence to investigate trait- and state-related neural system responses. Here, regional brain responses to positive, negative, and neutral emotional stimuli were assessed in individuals with BD during elevated, depressed, and euthymic mood states.

METHODS

One hundred and thirty-four subjects participated in functional magnetic resonance imaging scanning while processing faces depicting happy, fearful, and neutral expressions: 76 with BD (18 in elevated mood states, 19 depressed, 39 euthymic) and 58 healthy comparison (HC) individuals. Analyses were performed for BD trait- and mood state-related features.

RESULTS

Ventral anterior cingulate cortex (VACC), orbitofrontal cortex (OFC), and ventral striatum responses to happy and neutral faces were decreased in the BD group, compared to the HC group, and were not influenced by mood state. Elevated mood states were associated with decreased right rostral PFC activation to fearful and neutral faces, and depression was associated with increased left OFC activation to fearful faces.

CONCLUSIONS

The findings suggest that abnormal VACC, OFC, and ventral striatum responses to happy and neutral stimuli are trait features of BD. Acute mood states may be associated with additional lateralized abnormalities of diminished right rostral PFC responses to fearful and neutral stimuli in elevated states and increased left OFC responses to fearful stimuli in depressed states.

The functional neuroanatomy of bipolar disorder: a consensus model

OBJECTIVES

Functional neuroimaging methods have proliferated in recent years, such that functional magnetic resonance imaging, in particular, is now widely used to study bipolar disorder. However, discrepant findings are common. A workgroup was organized by the Department of Psychiatry, University of Cincinnati (Cincinnati, OH, USA) to develop a consensus functional neuroanatomic model of bipolar I disorder based upon the participants' work as well as that of others.

METHODS

Representatives from several leading bipolar disorder neuroimaging groups were organized to present an overview of their areas of expertise as well as focused reviews of existing data. The workgroup then developed a consensus model of the functional neuroanatomy of bipolar disorder based upon these data.

RESULTS

Among the participants, a general consensus emerged that bipolar I disorder arises from abnormalities in the structure and function of key emotional control networks in the human brain. Namely, disruption in early development (e.g., white matter connectivity and prefrontal pruning) within brain networks that modulate emotional behavior leads to decreased connectivity among ventral prefrontal networks and limbic brain regions, especially the amygdala. This developmental failure to establish healthy ventral prefrontal-limbic modulation underlies the onset of mania and ultimately, with progressive changes throughout these networks over time and with affective episodes, a bipolar course of illness.

CONCLUSIONS

This model provides a potential substrate to guide future investigations and areas needing additional focus are identified.

Working memory network alterations and associated symptoms in adults with ADHD and Bipolar Disorder

Attention-Deficit/Hyperactivity Disorder (ADHD) and Bipolar Disorder (BPD) co-occur frequently and represent a particularly morbid clinical form of both disorders, however underlying neural circuitry contributing to the comorbidity remain understudied. Our aim was to investigate functional brain circuitry during working memory in a group of participants who meet criteria for both disorders (ADHD + BPD), and to explore the relationship of symptoms of each disorder to brain function. We used fMRI to image brain activity in 18 male adults with both ADHD and BPD, and 18 healthy control participants matched one-to-one on age, sex, and handedness, while they performed a sequential letter N-back task. We investigated differences in activation between these groups, and also correlations of brain activity during the task to symptoms of ADHD and BPD independently. We found significant hypoactivity in the subjects with ADHD + BPD vs. controls across frontal and parietal regions, and further, found that BPD and ADHD symptoms related to activity in anatomically distinct regions that were respectively characterized by activation and suppression during task. We conclude that comorbid ADHD + BPD is associated with alterations across anterior and posterior nodes of the working memory network, and symptoms of each disorder are related to anatomically and functionally distinct brain regions.

An fMRI study of attentional control in the context of emotional distracters in euthymic adults with bipolar disorder

Inability to modulate attention away from emotional stimuli may be a key component of dysregulated emotion in bipolar disorder (BD). Previous studies of BD indicate abnormalities in neural circuitry underlying attentional control, yet few studies examined attentional control in the context of emotional distracters. We compared activity and connectivity in neural circuitry supporting attentional control and emotion processing among 22 individuals with BD type 1, currently remitted and euthymic, and 19 healthy controls. Participants performed an emotional n-back paradigm, comprising high and low attentional demand conditions, each with either emotional (happy, fearful), neutral or no face flanker distracters. During the high attentional control demand conditions without emotional distracters, BD individuals showed reduced activity relative to controls in dorsolateral prefrontal cortex, dorsal anterior cingulate cortex (dACC), and inferior parietal cortex. During the high attentional control demand conditions with fearful-face distracters, BD individuals showed greater activity than controls in these regions and amygdala and striatum. Relative to controls, BD individuals also showed abnormal patterns of effective connectivity between dACC and amygdala during high attentional control demand with emotional face distracters. Inter-episode bipolar disorder is characterized by abnormal recruitment of attentional control neural circuitry, especially in the context of emotionally distracting information.

Grey matter differences in bipolar disorder: a meta-analysis of voxel-based morphometry studies

OBJECTIVE

Several neuroimaging studies have reported structural brain differences in bipolar disorder using automated methods. While these studies have several advantages over those using region of interest techniques, no study has yet estimated a summary effect size or tested for between-study heterogeneity. We sought to address this issue using meta-analytic techniques applied for the first time in bipolar disorder at the level of the individual voxel.

METHODS

A systematic review identified 16 voxel-based morphometry (VBM) studies comparing individuals with bipolar disorder with unaffected controls, of which eight were included in the meta-analysis. In order to take account of heterogeneity, summary effect sizes were computed using a random-effects model with appropriate correction for multiple testing.

RESULTS

Compared with controls, subjects with bipolar disorder had reduced grey matter in a single cluster encompassing the right ventral prefrontal cortex, insula, temporal cortex, and claustrum. Study heterogeneity was widespread throughout the brain; though the significant cluster of grey matter reduction remained once these extraneous voxels had been removed. We found no evidence of publication bias (Eggers p = 0.63).

CONCLUSIONS

Bipolar disorder is consistently associated with reductions in right prefrontal and temporal lobe grey matter. Reductions elsewhere may be obscured by clinical and methodological heterogeneity.

Self-referential thinking, suicide, and function of the cortical midline structures and striatum in mood disorders: possible implications for treatment studies of mindfulness-based interventions for bipolar depression

Bipolar depression is often refractory to treatment and is frequently associated with anxiety symptoms and elevated suicide risk. There is a great need for adjunctive psychotherapeutic interventions. Treatments with effectiveness for depressive and anxiety symptoms as well as suicide-related thoughts and behaviors would be particularly beneficial. Mindfulness-based interventions hold promise, and studies of these approaches for bipolar disorder are warranted. The aim of this paper is to provide a conceptual background for such studies by reviewing key findings from diverse lines of investigation. Results of that review indicate that cortical midline structures (CMS) appear to link abnormal self-referential thinking to emotional dysregulation in mood disorders. Furthermore, CMS and striatal dysfunction may play a role in the neuropathology underlying suicide-related thoughts and behaviors. Thus, combining studies of mindfulness interventions targeting abnormal self-referential thinking with functional imaging of CMS and striatal function may help delineate the neurobiological mechanisms of action of these treatments.

Reduced prefrontal oxygenation during object and spatial visual working memory in unpolar and bipolar depression

Altered prefrontal brain activity (e.g. hypofrontality) during cognitive tasks such as working memory is a core neuroimaging marker in unipolar (UNI) and bipolar (BI) depression. The present study investigated for the first time UNI (n=16) and BI patients (n=14) in a working memory task including different processes (storage and matching) and components (object and spatial visual) with functional near-infrared spectroscopy (fNIRS) over the prefrontal cortex. In healthy controls (n=15) comparable to both patient groups, changes of oxygenated and deoxygenated haemoglobin indicated increased ventro-lateral, dorso-lateral prefrontal and superior frontal cortex activity for object and spatial visual working memory storage as compared to the control condition. In contrast, both patient groups showed diminished brain activity in all working memory conditions. Results revealed unspecific deficits that did not allow the differentiation between unipolar and bipolar depression in dependence of working memory processes or components. However, fNIRS can be considered as a valid, easy manageable, low cost and rapid tool for measuring (diminished) prefrontal cortex functions.

Brain structural and functional correlates of resilience to Bipolar Disorder

BACKGROUND

Resilient adaptation can be construed in different ways, but as used here it refers to adaptive brain responses associated with avoidance of psychopathology despite expressed genetic predisposition to Bipolar Disorder (BD). Although family history of BD is associated with elevated risk of affective morbidity a significant proportion of first-degree relatives remain free of psychopathology. Examination of brain structure and function in these individuals may inform on adaptive responses that pre-empt disease expression.

METHODS

Data presented here are derived from the Vulnerability to Bipolar Disorders Study (VIBES) which includes BD patients, asymptomatic relatives and controls. Participants underwent extensive investigations including brain structural (sMRI) and functional magnetic resonance imaging (fMRI). We present results from sMRI voxel-based-morphometry and from conventional and connectivity analyses of fMRI data obtained during the Stroop Colour Word Test (SCWT), a task of cognitive control during conflict resolution. All analyses were implemented using Statistical Parametric Mapping software version 5 (SPM5). Resilience in relatives was operationalized as the lifetime absence of clinical-range symptoms.

RESULTS

Resilient relatives of BD patients expressed structural, functional, and connectivity changes reflecting the effect of genetic risk on the brain. These included increased insular volume, decreased activation within the posterior and inferior parietal regions involved in selective attention during the SCWT, and reduced fronto-insular and fronto-cingulate connectivity. Resilience was associated with increased cerebellar vermal volume and enhanced functional coupling between the dorsal and the ventral prefrontal cortex during the SCWT.

CONCLUSIONS

Our findings suggests the presence of biological mechanisms associated with resilient adaptation of brain networks and pave the way for the identification of outcome-specific trajectories given a bipolar genotype.

Progression of amygdala volumetric abnormalities in adolescents after their first manic episode

OBJECTIVE

Although previous neuroimaging studies suggest that adolescents with bipolar disorder exhibit smaller amygdala volumes compared with healthy adolescents, whether these abnormalities are present at illness onset or instead develop over time remains unclear. The aim of this study was to conduct a prospective longitudinal investigation comparing amygdala neurodevelopment among adolescents after their first manic episode, adolescents with attention-deficit/hyperactivity disorder (ADHD), and healthy adolescents.

METHOD

A total of 30 adolescents hospitalized for their first manic/mixed episode associated with bipolar disorder, 29 adolescents with ADHD, and 24 demographically matched healthy teens underwent magnetic resonance imaging scanning at index assessment and approximately 12 months later. Adolescents with bipolar disorder were prospectively evaluated using diagnostic interviews and with symptom rating scales.

RESULTS

Mixed models examining the group × time effect for both left (p = .005) and right (p = .002) amygdala volumes were statistically significant. Change in left (p = .01) and right (p = .0008) amygdala volumes from baseline to 12 months were significantly different among groups. Specifically, left amygdala volumes increased over time in healthy adolescents (p = .008) and adolescents with ADHD (p = .0009), but not in adolescents with bipolar disorder (p = .3). Right amygdala volume increased over time in adolescents with ADHD (p < .001), but not in healthy adolescents nor in adolescents with bipolar disorder (p = .1 and p = .3, respectively). In adolescents with bipolar disorder, baseline total amygdala volume was significantly greater in those who subsequently achieved symptomatic recovery as compared with those who did not achieve recovery (p = .02).

CONCLUSIONS

Adolescents with mania do not exhibit normal increases in amygdala volume that occur during healthy adolescent neurodevelopment.

Toward a functional neuroanatomical signature of bipolar disorder: quantitative evidence from the neuroimaging literature

The present meta-analysis quantitatively reviewed the functional neuroimaging literature on bipolar disorder (BPD) to better characterize its neuroanatomical signature with respect to the influence of mood state, test conditions, and clinical demographics on regional brain activation. Fifty-five functional neuroimaging studies published between 1987 and 2010 met criteria for inclusion, encompassing a total of 774 adult patients with BPD and 810 healthy adult controls. A meta-analysis was conducted comparing the activation states of multiple brain regions in BPD patients and control subjects. Despite heterogeneity across studies, our findings support the view that limbic hyperactivity and frontal hypoactivity are neurobiological correlates of BPD. Our findings also highlight the involvement of many brain regions and circuits, as well as the critical role of mood state and test conditions in the functional impairments of BPD. This review represents the first attempt to quantitatively articulate the magnitude of functional brain abnormality in BPD, and, in so doing, provides a synthesis of evidence in line with current network models of the disorder. Overall, this review offers support for, and seeks to help guide, the continued use of functional neuroimaging as an informative probe into the complex neurobiology of BPD.

Aberrant emotional processing in posterior cortical midline structures in bipolar II depression

Bipolar II depression is a serious and disabling illness associated with significant impairment and high rates of suicide attempts. However, mechanisms underlying emotional dysregulation in this condition are poorly characterized. The goal of this work was to investigate one component of emotional processing in this disorder, brain activation associated with exposure to emotional faces. Functional MRI was used to study 16 unmedicated male subjects with bipolar II depression and 19 healthy male controls. The activation paradigm exposed subjects to happy, fearful and neutral faces. The two key findings of this study were as follows. First, bipolar subjects demonstrated significantly decreased activation in response to happy facial expression in the left posterior cortical midline structures (CMS) and frontal cortex. Second, depression severity was positively correlated with activation of the posterior CMS and other regions. Our results suggest that mechanisms involving CMS dysfunction may play a role in the neurobiology of bipolar II depression as has been demonstrated for unipolar illness. Further investigations of CMS function in bipolar spectrum disorders are warranted.

Working memory and attention deficits in adolescent offspring of schizophrenia or bipolar patients: comparing vulnerability markers

BACKGROUND

Working memory deficits abound in schizophrenia and attention deficits have been documented in schizophrenia and bipolar disorder. Adolescent offspring of patients may inherit vulnerabilities in brain circuits that subserve these cognitive domains. Here we assess impairments in offspring of schizophrenia (SCZ-Offspring) or bipolar (BP-Offspring) patients compared to controls (HC) with no family history of mood or psychotic disorders to the second degree.

METHODS

Three groups (n=100 subjects; range: 10-20 yrs) of HC, SCZ-Offspring and BP-Offspring gave informed consent. Working memory was assessed using a delayed spatial memory paradigm with two levels of delay (2s & 12s); sustained attention processing was assessed using the Continuous Performance Task-Identical Pairs version.

RESULTS

SCZ-Offspring (but not BP-Offspring) showed impairments in working memory (relative to HC) at the longer memory delay indicating a unique deficit. Both groups showed reduced sensitivity during attention but only BP-Offspring significantly differed from controls.

CONCLUSIONS

These results suggest unique (working memory/dorsal frontal cortex) and potentially overlapping (attention/fronto-striatal cortex) vulnerability pathways in adolescent offspring of patients with schizophrenia and bipolar disorder. Working memory and attention assessments in these offspring may assist in the clinical characterization of the adolescents vulnerable to SCZ or BP.

Progressive neurostructural changes in adolescent and adult patients with bipolar disorder

OBJECTIVES

Several lines of evidence suggest that bipolar disorder is associated with progressive changes in gray matter volume (GMV), particularly in brain structures involved in emotional regulation and expression. The majority of these studies however, have been cross-sectional in nature. In this study we compared baseline and follow-up scans in groups of bipolar disorder and healthy subjects. We hypothesized bipolar disorder subjects would demonstrate significant GMV changes over time.

METHODS

A total of 58 bipolar disorder and 48 healthy subjects participated in structural magnetic resonance imaging (MRI). Subjects were rescanned 3-34 months after their baseline MRI. MRI images were segmented, normalized to standard stereotactic space, and compared voxel-by-voxel using statistical parametrical mapping software (SPM2). A model was developed to investigate differences in GMV at baseline, and associated with time and episodes, as well as in comparison to healthy subjects.

RESULTS

We observed increases in GMV in bipolar disorder subjects across several brain regions at baseline and over time, including portions of the prefrontal cortex as well as limbic and subcortical structures. Time-related changes differed to some degree between adolescent and adult bipolar disorder subjects. The interval between scans positively correlated with GMV increases in bipolar disorder subjects in portions of the prefrontal cortex, and both illness duration and number of depressive episodes were associated with increased GMV in subcortical and limbic structures.

CONCLUSIONS

Our findings support suggestions that widely observed progressive neurofunctional changes in bipolar disorder patients may be related to structural brain abnormalities in anterior limbic structures. Abnormalities largely involve regions previously noted to be integral to emotional expression and regulation, and appear to vary by age.

Visuospatial working memory deficits in remitted patients with bipolar disorder: susceptibility to the effects of GABAergic agonists

OBJECTIVES

Visuospatial working memory (VSWM) deficit under high working memory (WM) load deserves further investigation as a potential trait marker for bipolar disorder (BPD). However, VSWM performances may depend on basic neurocognitive processes and are possibly compromised by neurocognitive effects of psychotropic medications.

METHODS

A total of 32 remitted BPD patients and 39 healthy controls undertook parametric VSWM tasks and assessments for selective attention, sustained attention, psychomotor speed, mental flexibility, and Wechsler Adult Intelligence Scale-III full IQ. Using a multivariate model and trend analysis and controlling for other basic neurocognitive ability, the effects of mood stabilizers, antipsychotics, GABAergic agonists, and anticholinergics on VSWM performances were explored by post-hoc analysis comparing performances across WM loads between healthy controls and patients treated and not treated with a specific medication.

RESULTS

Remitted BPD patients showed more pronounced performance declines in VSWM performances as WM loads increased, indicating inefficient VSWM processing. The VSWM deficits of remitted patients were independent of their impairments in attentional processes or psychomotor speed. Among the medications, only GABAergic agonists were associated with impaired VSWM performances.

CONCLUSIONS

Remitted BPD patients had WM-load-dependent VSWM processing deficits after controlling for neurocognitive performances. As these deficits were associated with the use of GABAergic agonists, altered GABAergic neurotransmission might be involved with the underlying mechanisms of the impaired VSWM processing of BPD. Since GABAergic agonist use is often continued from the acute to the remitted phase in BPD and might potentially affect the functional recovery, clinicians should be aware of these neurocognitive side effects, even at low dosages. Close monitoring and timely discontinuation of GABAergic agonists is of utmost importance for clinical practice.

A functional MRI study of working memory in adolescents and young adults at genetic risk for bipolar disorder: preliminary findings

OBJECTIVES

In this report, we seek to (i) identify a potential neuroimaging endophenotype for bipolar disorder (BD) in emotion regulatory and autonomic circuitry in young first-degree relatives of persons with BD; and (ii) replicate our previous work identifying the functional neuroanatomy of working memory (WM) in an older sample of relatives of persons with BD.

METHODS

Ten adolescent and young adult (age 13-24) unmedicated, non-ill, first-degree relatives of persons with BD (RELS) and 10 demographically comparable healthy controls performed a 2-back WM task and a 0-back control task during functional magnetic resonance imaging (fMRI). fMRI data were collected on a 1.5 Tesla scanner and analyzed using SPM-2. Mood was assessed on the day of scanning.

RESULTS

The groups did not differ on any demographic, neuropsychological, or in-scanner task performance variables. In contrast to controls, RELS showed (i) weak task-dependent modulation activity in the cerebellar vermis (CV), insula, and amygdala/parahippocampal region, and (ii) exaggerated modulation of activity in the frontopolar cortex and brainstem, even after controlling for potential confounders. Many of the group differences were driven by differences in activity in the low-level (0-back) baseline task.

CONCLUSIONS

Young, unmedicated RELS exhibited altered task-dependent modulation of frontopolar, CV, and insula activity during WM, especially during the low-level (0-back) baseline task. Results are largely consistent with our initial study of older adult RELS, suggesting these alterations may represent biomarkers of genetic risk for BD.

A quantitative meta-analysis of fMRI studies in bipolar disorder

OBJECTIVES

Functional magnetic resonance imaging (fMRI) has been widely used to identify state and trait markers of brain abnormalities associated with bipolar disorder (BD). However, the primary literature is composed of small-to-medium-sized studies, using diverse activation paradigms on variously characterized patient groups, which can be difficult to synthesize into a coherent account. This review aimed to synthesize current evidence from fMRI studies in midlife adults with BD and to investigate whether there is support for the theoretical models of the disorder.

METHODS

We used voxel-based quantitative meta-analytic methods to combine primary data on anatomical coordinates of activation from 65 fMRI studies comparing normal volunteers (n = 1,074) and patients with BD (n = 1,040).

RESULTS

Compared to normal volunteers, patients with BD underactivated the inferior frontal cortex (IFG) and putamen and overactivated limbic areas, including medial temporal structures (parahippocampal gyrus, hippocampus, and amygdala) and basal ganglia. Dividing studies into those using emotional and cognitive paradigms demonstrated that the IFG abnormalities were manifest during both cognitive and emotional processing, while increased limbic activation was mainly related to emotional processing. In further separate comparisons between healthy volunteers and patient subgroups in each clinical state, the IFG was underactive in manic but not in euthymic and depressed states. Limbic structures were not overactive in association with mood states, with the exception of increased amygdala activation in euthymic states when including region-of-interest studies.

CONCLUSIONS

In summary, our results showed abnormal frontal-limbic activation in BD. There was attenuated activation of the IFG or ventrolateral prefrontal cortex, which was consistent across emotional and cognitive tasks and particularly related to the state of mania, and enhanced limbic activation, which was elicited by emotional and not cognitive tasks, and not clearly related to mood states.

Synaptic plasticity in the pathophysiology and treatment of bipolar disorder

Emerging evidence suggests that synaptic plasticity is intimately involved in the pathophysiology and treatment of bipolar disorder (BPD). Under certain conditions, over-strengthened and/or weakened synapses at different circuits in the brain could disturb brain functions in parallel, causing manic-like or depressive-like behaviors in animal models. In this chapter, we summarize the regulation of synaptic plasticity by medications, psychological conditions, hormones, and neurotrophic factors, and their correlation with mood-associated animal behaviors. We conclude that increased serotonin, norepinephrine, dopamine, brain-derived neurotrophic factor (BDNF), acute corticosterone, and antidepressant treatments lead to enhanced synaptic strength in the hippocampus and also correlate with antidepressant-like behaviors. In contrast, inhibiting monoaminergic signaling, long-term stress, and pathophysiological concentrations of cytokines weakens glutamatergic synaptic strength in the hippocampus and is associated with depressive-like symptoms.

Striatal structure and function in mood disorders: a comprehensive review

OBJECTIVES

  A large and diverse literature has implicated abnormalities of striatal structure and function in both unipolar and bipolar disorder. Recent functional imaging studies have greatly expanded this body of research. The aim of this review is to provide a comprehensive and critical appraisal of the relevant literature.

METHODS

  A total of 331 relevant articles were reviewed to develop an integrated overview of striatal function in mood disorders.

RESULTS

  There is compelling evidence from multiple studies that functional abnormalities of the striatum and greater corticostriatal circuitry exist in at least some forms of affective illness. The literature does not yet provide data to determine whether these aberrations represent primary pathology or they contribute directly to symptom expression. Finally, there is considerable evidence that bipolar disorder may be associated with striatal hyperactivity and some suggestion that unipolar illness may be associated with hypoactivation.

CONCLUSIONS

  Additional research investigating striatal function in affective disorders will be critical to the development of comprehensive models of the neurobiology of these conditions.

Neurosurgical treatment of bipolar depression: defining treatment resistance and identifying surgical targets

OBJECTIVES

Bipolar disorder (BD) is a complex psychiatric disorder that is often underrecognized, misdiagnosed, and challenging to detect. During the past decade, substantial progress has been made in the development of pharmacotherapeutic and psychosocial interventions for various phases of BD. Notwithstanding these developments, the majority of BD individuals, and particularly patients with bipolar depression, receiving guideline concordant care do not experience syndromal or functional recovery, underscoring the need for novel treatments. Early success with deep brain stimulation (DBS) in the treatment of major depressive episodes as part of major depressive disorder (MDD) has provided the impetus to explore its application in other treatment-resistant psychiatric disorders, notably BD. Herein, we provide the rationale for employing DBS as an alternative treatment avenue in individuals with bipolar depression.

METHODS

We conducted a PubMed literature search, focusing on English language articles beginning in 1950 to the present day, and employed the following search terms: bipolar disorder, neurosurgery, deep brain stimulation, neuroimaging, and circuitry. Search results were then manually reviewed and relevant articles selected for analysis. Relevance was determined by author consensus and overall manuscript quality. We also reviewed articles on currently available treatment options for BD in order to develop a coherent and practical definition of treatment resistance with a focus on surgical intervention.

RESULTS

Several lines of evidence indicate that although mania is the defining feature of bipolar I disorder, depressive symptoms and episodes dominate the longitudinal course, account for most of the illness burden including premature mortality, and are least responsive to contemporary treatments. Disease models in bipolar depression implicate abnormalities in the structure and function of discrete neural circuits that subserve affective processing and cognitive function with the subgenual cingulate cortex occupying a central role. Modulation of the cingulate cortex with DBS in treatment-resistant MDD populations has proven to offer acute and sustained antidepressant effects, suggesting possible benefits for other mood disorder populations.

CONCLUSIONS

A surgical intervention for bipolar depression would not only be a proof of concept regarding disease modeling but also an important and novel treatment avenue for individuals affected by bipolar depression.

Altered neural function in pediatric bipolar disorder during reversal learning

OBJECTIVE

Data documenting the functional impairment associated with the diagnosis of bipolar disorder (BD) in children and adolescents highlight the need for greater understanding of its pathophysiology. Toward that end, we demonstrated previously that BD youth have behavioral deficits on reversal learning tasks. On such tasks, participants must first acquire a stimulus/response relationship through trial-and-error learning, and then discern when the stimulus/reward relationship reverses. Here, we use event-related functional magnetic resonance imaging (fMRI) to elucidate neural correlates of reversal learning deficits in euthymic BD youth compared to typically developing controls.

METHOD

  We compared euthymic pediatric BD participants (n = 16) versus age-, sex-, and IQ-matched controls (n = 16). Our main outcome measure was blood oxygen level-dependent (BOLD) signal measured with fMRI during an event-related probabilistic reversal task.

RESULTS

Pediatric BD participants had significantly greater neural activity than controls in fronto-parietal regions during the reversal phase, particularly in response to punished reversal errors (p < 0.05 corrected for multiple comparisons).

CONCLUSIONS

Our current study suggests that during reversal learning, BD youths inefficiently recruit regions associated with processing response conflict and implementing alternative responses, including subdivisions of the frontal cortex and the parietal cortex. Such deficits are present in euthymic BD youth. Further work is necessary to evaluate the specificity of such alterations.

Fronto-temporal spontaneous resting state functional connectivity in pediatric bipolar disorder

BACKGROUND

The recent upsurge in interest about pediatric bipolar disorder (BD) has spurred the need for greater understanding of its neurobiology. Structural and functional magnetic resonance imaging studies have implicated fronto-temporal dysfunction in pediatric BD. However, recent data suggest that task-dependent neural changes account for a small fraction of the brain's energy consumption. We now report the first use of task-independent spontaneous resting state functional connectivity (RSFC) to study the neural underpinnings of pediatric BD.

METHODS

We acquired task-independent RSFC blood oxygen level-dependent functional magnetic resonance imaging scans while participants were at rest and also a high-resolution anatomical image (both at three Tesla) in BD and control youths (n = 15 of each). We focused, on the basis of prior research, on the left dorsolateral prefrontal cortex (DLPFC), amygdala, and accumbens. Image processing and group-level analyses followed that of prior work.

RESULTS

Our primary analysis showed that pediatric BD participants had significantly greater negative RSFC between the left DLPFC and the right superior temporal gyrus versus control subjects. Secondary analyses using partial correlation showed that BD and control youths had opposite phase relationships between spontaneous RSFC fluctuations in the left DLPFC and right superior temporal gyrus.

CONCLUSIONS

Our data indicate that pediatric BD is characterized by altered task-independent functional connectivity in a fronto-temporal circuit that is also implicated in working memory and learning. Further study is warranted to determine the effects of age, gender, development, and treatment on this circuit in pediatric BD.

Fronto-temporal dysregulation in asymptomatic bipolar I patients: a paired associate functional MRI study

Bipolar disorder is associated with persistent declarative memory disturbances, but the neural basis of these deficits is not well understood. We used fMRI to investigate brain activity during performance on a face-name paired associate task, which allows for the dissociation of encoding and recall-related memory processes. Fifteen clinically remitted bipolar I disorder patients and 24 demographically matched healthy comparison subjects were scanned during task performance. At the voxel level, bipolar patients showed reduced cortical activation, relative to controls, in multiple task-related brain regions during encoding. During recognition, bipolar patients under-activated left hippocampal and parahippocampal regions, despite adequate task performance. Region of interest analyses indicated that, during encoding, bipolar patients had greater bilateral dorsolateral prefrontal (DLPFC) activity than healthy subjects. In contrast, during recognition patients showed hypo-activation relative to controls in the right, but not the left, DLPFC. Although hippocampal activity did not differ between groups during encoding, bipolar patients failed to activate hippocampal regions to the same extent as healthy subjects during recognition. Finally, while better task performance was associated with recognition-related hippocampal activity in healthy subjects, bipolar patients showed an inverse relationship between task performance and hippocampal activity. Remitted bipolar patients over-engaged dorsolateral prefrontal regions when learning face-name pairs, but relative hypoactivation in both prefrontal and medial temporal regions during recognition. These findings suggest a neural basis for the long-term memory deficits consistently observed in patients with bipolar disorder; further, as these patterns appear in symptomatically remitted patients, they are unlikely to be an artifact of mood symptoms.

Cortico-basal ganglia circuitry: a review of key research and implications for functional connectivity studies of mood and anxiety disorders

There is considerable evidence that dysfunction of the cortico-basal ganglia circuits may be associated with several mood and anxiety disorders. However, it is unclear whether circuit abnormalities contribute directly either to the neurobiology of these conditions or to the manifestation of symptoms. Understanding the role of these pathways in psychiatric illness has been limited by an incomplete characterization of normal function. In recent years, studies using animal models and human functional imaging have greatly expanded the literature describing normal cortico-basal ganglia circuit function. In this paper, recent key studies of circuit function using human and animal models are reviewed and integrated with findings from other studies conducted over the previous decades. The literature suggests several hypotheses of cortico-basal ganglia circuitry function in mood and anxiety disorders that warrant further exploration. Hypotheses are proposed herein based upon the cortico-basal ganglia mechanisms of: (1) feedforward and feedback control, (2) circuit integration and (3) emotional control. These are presented as models of circuit function, which may be particularly relevant to future investigations using neuroimaging and functional connectivity analyses.

Genetic analysis of nitric oxide synthase 1 variants in schizophrenia and bipolar disorder

Nitric oxide (NO) is a neurotransmitter that acts as a second messenger of the N-methyl-D-aspartate receptor and interacts with the dopaminergic and the serotonergic systems. NO involvement in pathological processes relevant to neuropsychiatric disorders stems from its ability to modulate certain forms of synaptic plasticity, and from its capacity to be transformed to a highly active free radical. Additionally, multiple links have been reported between the NO-producing enzyme, nitric oxide synthase (NOS) 1, and both schizophrenia and bipolar disorder (BPD). RNA and DNA isolated from dorsolateral-prefrontal cortices of schizophrenia patients, bipolar patients and controls (n = 26, 30 and 29, respectively) were donated by the Stanley Foundation Brain Collection. Gene expression was measured by Real-Time-PCR. Genetic polymorphisms were genotyped by restriction-fragment length-polymorphism analysis, and by product-size determination of PCR products amplified with a fluorescent primer.Expression analysis of pan-NOS1, as well as of 2 of its isoforms, "NOS1_1d" and "NOS1_1f", which differ in their first exons and translational strength, revealed a trend for pan-NOS1 over-expression (P = 0.075) in schizophrenia patients (1.33-fold), and significant over-expression (P < 0.05) of NOS1_1d and NOS1_1f in this group (1.54-fold and 1.61-fold, respectively). No expressional alteration was observed in BPD. Polymorphisms at the promoters of NOS1_1d and NOS1_1f, previously shown to be functional in vitro, revealed no significant allelic or genotypic differences among clinical groups and showed no effect on these transcripts' expression. In conclusion, understanding the molecular mechanisms underlying the over-expression of specific NOS1 isoforms, which is unique to schizophrenia, may assist in identifying targets for new drugs.

Region and diagnosis-specific changes in synaptic proteins in schizophrenia and bipolar I disorder

Aberrant regulation of synaptic function is thought to play a role in the aetiology of psychiatric disorders, including schizophrenia and bipolar disorder. Normal neurotransmitter release is dependent on a complex group of presynaptic proteins that regulate synaptic vesicle docking, membrane fusion and fission, including synaptophysin, syntaxin, synaptosomal-associated protein-25 (SNAP-25), vesicle-associated membrane protein (VAMP), alpha-synuclein and dynamin I. In addition, structural and signalling proteins such as neural cell adhesion molecule (NCAM) maintain the integrity of the synapse. We have assessed the levels of these important synaptic proteins using Western blots, in three cortical regions (BA10, 40 and 46) obtained post-mortem from subjects with bipolar 1 disorder, schizophrenia or no history of a psychiatric disorder. In bipolar 1 disorder cortex (parietal; BA40), we found a significant increase in the expression of SNAP-25, and a significant reduction in alpha-synuclein compared with controls. These changes in presynaptic protein expression are proposed to inhibit synaptic function in bipolar 1 disorder. In schizophrenia, a significant reduction in the ratio of the two major membrane-bound forms of NCAM (180 and 140) was observed in BA10. The distinct functions of these two NCAM forms suggest that changes in the comparative levels of these proteins could lead to a destabilisation of synaptic signalling. Our data support the notion that there are complex and region-specific alterations in presynaptic proteins that may lead to alterations in synaptic activity in both schizophrenia and bipolar disorder.

The functional neuroanatomy of bipolar disorder

In this manuscript, research articles using functional magnetic resonance imaging (fMRI) to study adult patients with bipolar disorder were reviewed. The findings from these studies identify altered brain activation in five regions in cortico-limbic pathways responsible for emotional regulation: portions of the prefrontal cortex; anterior cingulate cortex; amygdala; thalamus; and striatum. The most consistent findings were overactivation of amygdala, striatum, and thalamus. Findings in prefrontal cortex were less consistent, but most studies also showed increased activation in ventrolateral and dorsolateral prefrontal cortical areas. Excessive activation in brain regions associated with emotional regulation may contribute to the affective symptoms of bipolar disorder. However, there are several important limitations in this body of research. Even when similar tasks were used, brain activation was often discrepant among studies. Most fMRI studies examined small samples (ten or fewer bipolar subjects) limiting statistical power. Additionally, most studies were confounded by patients taking psychotropic medications. Nonetheless, from this work an anterior limbic over-activation model of bipolar disorder is emerging.

Functional neuroimaging studies of bipolar disorder: examining the wide clinical spectrum in the search for disease endophenotypes

Bipolar disorder (BP) is among the top ten most disabling illnesses worldwide. This review includes findings from recent studies employing functional neuroimaging to examine functional abnormalities in neural systems underlying core domains of the psychopathology in BP: emotion processing, emotion regulation and executive control, and common comorbid features of BP, that are relevant to the wide spectrum of BP rather than focused on the more traditional BPI subtype, and that may facilitate future identification of diagnostically-relevant biomarkers of the disorder. In addition, an emerging number of studies are reviewed that demonstrate the use of neuroimaging to elucidate biomarkers whose identification may help to (1) identify at-risk individuals who will subsequently develop the illness to facilitate early intervention, (2) identify targets for treatment and markers of treatment response. The use of newer neuroimaging techniques and potential confounds of psychotropic medication upon neuroimaging findings in BP are also examined. These approaches will help to improve diagnosis and the mental well-being of all individuals with BP.

fMRI abnormalities in dorsolateral prefrontal cortex during a working memory task in manic, euthymic and depressed bipolar subjects

Neuropsychological studies of subjects with bipolar disorder suggest impairment of working memory not only in acute mood states, but also while subjects are euthymic. Using fMRI to probe working memory regions in bipolar subjects in different mood states, we sought to determine the functional neural basis for these impairments. Typical working memory areas in normal populations include dorsolateral prefrontal cortex (BA9/46) and the posterior parietal cortex (BA40). We evaluated the activation in these regions using an n-back task in 42 bipolar subjects (13 manic, 15 euthymic and 14 depressed subjects) and 14 control subjects. While both control and bipolar subjects performed similarly on the task, bipolar subjects in all three mood states showed a significant reduction in activation in right BA9/46 and right BA40. Patients with bipolar disorder exhibit significantly attenuated neural activation in working memory circuits, independent of mood state. The reduction of neural activation may suggest a trait-related deficit. Subjects with bipolar disorder activated other additional frontal and temporal regions, perhaps as a compensatory mechanism, but this remains to be further explored.

Pathological amygdala activation during working memory performance: Evidence for a pathophysiological trait marker in bipolar affective disorder

Recent evidence suggests that deficits of working memory may be a promising neurocognitive endophenotype of bipolar affective disorder. However, little is known about the neurobiological correlates of these deficits. The aim of this study was to determine possible pathophysiological trait markers of bipolar disorder in neural circuits involved in working memory. Functional magnetic resonance imaging was performed in 18 euthymic bipolar patients and 18 matched healthy volunteers using two circuit-specific experimental tasks established by prior systematic neuroimaging studies of working memory. Both euthymic bipolar patients and healthy controls showed working memory-related brain activations that were highly consistent with findings from previous comparable neuroimaging studies in healthy subjects. While these patterns of brain activation were completely preserved in the bipolar patients, only the patients exhibited activation of the right amygdala during the articulatory rehearsal task. In the same task, functional activation in right frontal and intraparietal cortex and in the right cerebellum was significantly enhanced in the patients. These findings indicate that the right amygdala is pathologically activated in euthymic bipolar patients during performance of a circuit-specific working memory task (articulatory rehearsal). This pathophysiological abnormality appears to be a trait marker in bipolar disorders that can be observed even in the euthymic state and that seems to be largely independent of task performance and medication.

Alterations in functional activation in euthymic bipolar disorder and schizophrenia during a working memory task

Dysfunctions in prefrontal cortical networks are thought to underlie working memory (WM) impairments consistently observed in both subjects with bipolar disorder and schizophrenia. It remains unclear, however, whether patterns of WM-related hemodynamic responses are similar in bipolar and schizophrenia subjects compared to controls. We used fMRI to investigate differences in blood oxygen level dependent activation during a WM task in 21 patients with euthymic bipolar I, 20 patients with schizophrenia, and 38 healthy controls. Subjects were presented with four stimuli (abstract designs) followed by a fifth stimulus and required to recall whether the last stimulus was among the four presented previously. Task-related brain activity was compared within and across groups. All groups activated prefrontal cortex (PFC), primary and supplementary motor cortex, and visual cortex during the WM task. There were no significant differences in PFC activation between controls and euthymic bipolar subjects, but controls exhibited significantly increased activation (cluster-corrected P < 0.05) compared to patients with schizophrenia in prefrontal regions including dorsolateral prefrontal cortex (DLPFC). Although the bipolar group exhibited intermediate percent signal change in a functionally defined DLPFC region of interest with respect to the schizophrenia and control groups, effects remained significant only between patients with schizophrenia and controls. Schizophrenia and bipolar disorder may share some behavioral, diagnostic, and genetic features. Differences in the patterns of WM-related brain activity across groups, however, suggest some diagnostic specificity. Both patient groups showed some regional task-related hypoactivation compared to controls across the brain. Within DLPFC specifically, patients with schizophrenia exhibited more severe WM-related dysfunction than bipolar subjects.

An fMRI study of working memory in persons with bipolar disorder or at genetic risk for bipolar disorder

First-degree relatives of persons with bipolar disorders (BDs) carry elevated risk for the illness, and manifest deficits in attention and memory (possible "endophenotypes"). However, there is only one published functional magnetic resonance imaging (fMRI) study of candidate endophenotypes in BD. We used fMRI to examine brain function in BD and in first-degree relatives performing a 2-back working memory (WM) task, and correlated brain activity with mood measures taken at the scanning session. Subjects (age 32-46) were 19 persons with BD, 18 unmedicated, non-psychotic first-degree relatives (RELs) of persons with BD, and 19 matched controls, ascertained from a long-term follow-up of a prenatal cohort study in New England. fMRI signal during 2-back and 0-back WM tasks was measured on a Siemens 1.5T MR scanner. fMRI data were analyzed using SPM-2. Persons with BD and RELs failed to suppress activation in the left anterior insula (BA 13) during WM, whereas controls suppressed activation. Compared to controls, RELs also failed to suppress activation in the orbitofrontal cortex (OFC) and superior parietal cortex. Controls and RELs exhibited greater activation than BD individuals in the left frontopolar cortex (BA 10) during WM. Results remained significant after controlling for confounders except for mild attenuation of OFC findings. Significant correlations between brain activity, mood, and WM suggest that activity in WM circuits is affected by activity in emotion-regulatory circuits. Persons with BD and RELs exhibit altered activity in the frontopolar cortex and insula, which may represent biomarkers of genetic risk for BD.

Functional neuroimaging research in bipolar disorder

Functional neuroimaging techniques have been important research tools in the study of bipolar disorder (BPD). These methods provide measures of regional brain functioning that reflect the mental state at the time of scanning and have helped to elucidate both state and trait features of BPD. This chapter will review converging functional neuroimaging evidence implicating state and trait dysfunction in a ventral prefrontal cortex-amygdala neural system in BPD. Emerging evidence that suggests a developmental progression in dysfunction in this neural system over the course of adolescence will be considered. Finally, new research approaches that have begun to reveal the contribution of specific genetic mechanisms to regional dysfunction in the disorder, potential salutary effects of medications, and structure-function relationships will be discussed.

Risk and resilience in bipolar disorder: rationale and design of the Vulnerability to Bipolar Disorders Study (VIBES)

BD (bipolar disorder) is among the ten most significant causes of disability worldwide. Neuroscientists and clinicians have yet to meet the challenge of reducing this disability burden. The main obstacle to date has been our incomplete understanding of the pathophysiology of BD which thwarts primary prevention and early diagnosis and hinders effective treatment. There is a need to move beyond diagnostic approaches based purely on behavioural observation, as they lack reliability and biological validity. The present article reviews the evidence for cognitive, brain structural and functional correlates of genetic predisposition to BD and highlights biological markers of risk as well as factors that might protect against disease expression. It also outlines the rational and design of the Vulnerability to Bipolar Disorders Study (VIBES), which exemplifies a promising approach to delineating biological mechanisms mediating risk, resilience and disease expression in BD.

Neurobiological trait abnormalities in bipolar disorder

Dissecting trait neurobiological abnormalities in bipolar disorder (BD) from those characterizing episodes of mood disturbance will help elucidate the aetiopathogenesis of the illness. This selective review highlights the immunological, neuroendocrinological, molecular biological and neuroimaging abnormalities characteristic of BD, with a focus on those likely to reflect trait abnormalities by virtue of their presence in euthymic patients or in unaffected relatives of patients at high genetic liability for illness. Trait neurobiological abnormalities of BD include heightened pro-inflammatory function and hypothalamic-pituitary-adrenal axis dysfunction. Dysfunction in the intracellular signal transduction pathway is indicated by elevated protein kinase A activity and altered intracellular calcium signalling. Consistent neuroimaging abnormalities include the presence of ventricular enlargement and white matter abnormalities in patients with BD, which may represent intermediate phenotypes of illness. In addition, spectroscopy studies indicate reduced prefrontal cerebral N-acetylaspartate and phosphomonoester concentrations. Functional neuroimaging studies of euthymic patients implicate inherently impaired neural networks subserving emotional regulation, including anterior limbic, ventral and dorsal prefrontal regions. Despite heterogeneous samples and conflicting findings pervading the literature, there is accumulating evidence for the existence of neurobiological trait abnormalities in BD at various scales of investigation. The aetiopathogenesis of BD will be better elucidated by future clinical research studies, which investigate larger and more homogenous samples and employ a longitudinal design to dissect neurobiological abnormalities that are underlying traits of the illness from those related to episodes of mood exacerbation or pharmacological treatment.

Genetic variation in the G72 (DAOA) gene affects temporal lobe and amygdala structure in subjects affected by bipolar disorder

BACKGROUND

Variation in the G72 (DAOA) gene is understood to convey susceptibility for bipolar disorder through an uncertain mechanism. Little is known about the structural brain phenotypes associated with this gene. We hypothesised that reductions in temporal lobe and amygdala gray matter would be associated with variation at two loci in the gene for which evidence of genetic linkage has been repeatedly demonstrated.

METHODS

We examined the temporal lobe and amygdala gray matter associations of the risk variants M23 and M24 at the 5' end of the gene encoding G72 in 81 controls and 38 people with bipolar disorder.

RESULTS

Genetic variation at both the M23 and M24 loci in G72 were associated with decreased gray matter density within the left temporal pole in people with bipolar disorder. M23 was also associated with reductions in right amygdala gray matter density. The genetic imaging associations were found only in patients with bipolar disorder.

CONCLUSIONS

Genetic variation at single nucleotide polymorphisms in the G72 gene previously associated with bipolar disorder is related to reductions in temporal pole and amygdala gray matter structure in people with bipolar disorder.

Remission from mania is associated with a decrease in amygdala activation during motor response inhibition

OBJECTIVES

Neuroimaging studies of bipolar disorder (BD) have provided evidence of brain functional abnormalities during both the states of mania and remission. However, the differences in brain function between these two states are still poorly known. In the current study, we aimed to use a longitudinal design to examine the functional changes associated with symptomatic remission from mania within the brain network underlying motor response inhibition.

METHODS

Using event-related functional magnetic resonance imaging (fMRI), 10 BD patients and 10 healthy subjects were imaged twice while performing a Go/NoGo task. Patients were in a manic state when they underwent the first scan and fully remitted during the second scan. A mixed-effect ANOVA was used to identify brain regions showing differences in activation change over time between the two groups.

RESULTS

The left amygdala was the only brain region to show a time-dependent change in activation that was significantly different between BD patients and healthy subjects. Further analyses revealed that this difference arose from the patient group, in which amygdala activation was decreased between mania and subsequent remission.

CONCLUSIONS

This finding suggests that a decrease in left amygdala responsiveness is a critical phenomenon associated with remission from mania. It emphasizes the relevance of longitudinal approaches for identifying neurofunctional modifications associated with mood changes in BD.

Altered prefrontal lobe oxygenation in bipolar disorder: a study by near-infrared spectroscopy

BACKGROUND

Previous studies have reported prefrontal cortex (PFC) pathophysiology in bipolar disorder.

METHOD

We examined the hemodynamics of the PFC during resting and cognitive tasks in 29 patients with bipolar disorder and 27 healthy controls, matched for age, verbal abilities and education. The cognitive test battery consisted of letter and category fluency (LF and CF), Sets A and B of the Raven's Colored Progressive Matrices (RCPM-A and RCPM-B) and the letter cancellation test (LCT). The tissue oxygenation index (TOI), the ratio of oxygenated hemoglobin (HbO2) concentration to total hemoglobin concentration, was measured in the bilateral PFC by spatially resolved near-infrared spectroscopy. Changes in HbO2 concentration were also measured.

RESULTS

The bipolar group showed slight but significant impairment in performance for the non-verbal tasks (RCPM-A, RCPM-B and LCT), with no significant between-group differences for the two verbal tasks (LF and CF). A group x task x hemisphere analysis of variance (ANOVA) on the TOI revealed an abnormal pattern of prefrontal oxygenation across different types of cognitive processing in the bipolar group. Post hoc analyses following a group x task x hemisphere ANOVA on HbO2 concentration revealed that the bipolar group showed a greater increase in HbO2 concentration in the LCT and in RCPM-B, relative to controls.

CONCLUSIONS

Both indices of cortical activation (TOI and HbO2 concentration) indicated a discrepancy in the PFC function between verbal versus non-verbal processing, indicating task-specific abnormalities in the hemodynamic control of the PFC in bipolar disorder.