Regional cerebral cortical thinning in bipolar disorder

Cortical plasticity following nerve transfer in the upper extremity

With increasing clinical experience, peripheral nerve surgeons have come to appreciate the important role that cortical plasticity and motor relearning play in functional recovery following a nerve transfer. Neurostimulation (transcranial magnetic stimulation), and neuroimaging (functional MRI, structural MRI, magnetoencephalography) measure different aspects of cortical physiology and when used together are powerful tools in the study of cortical plasticity. The mechanisms of cortical plasticity, according to current and widely accepted opinions, involve the unmasking of previously ineffective connections or the sprouting of intact afferents from adjacent cortical or subcortical territories. Although significant strides have been made in our understanding of cortical plasticity following nerve transfer and during motor relearning, a great deal remains that we do not understand. Cortical plasticity and its manipulation may one day become important contributors to improve functional outcome following nerve transfer.

Time-lapse mapping of cortical changes in schizophrenia with different treatments

Using time-lapse maps, we visualized the dynamics of schizophrenia progression, revealing spreading cortical changes that depend on the type of antipsychotic treatment. Dynamic, 4-dimensional models of disease progression were created from 4 repeated high-resolution brain magnetic resonance imaging scans of 36 first-episode schizophrenia patients (30 men/6 women; mean age: 24.2 +/- 5.1 SD years) randomized to haloperidol (HAL) (n = 15) or olanzapine (OLZ) treatment (n = 21), imaged at baseline, 3, 6, and 12 months (144 scans). Based on surface-based cortical models and point-by-point measures of gray matter volume, we generated time-lapse maps for each treatment. Disease trajectories differed for atypical versus typical neuroleptic drugs. A rapidly advancing parietal-to-frontal deficit trajectory, in HAL-treated patients, mirrored normal cortical maturation but greatly intensified. The disease trajectory advanced even after symptom normalization, involving the frontal cortex within 12 months with typical drug treatment. Areas with fastest tissue loss shifted anteriorly in the first year of psychosis. This trajectory was not seen with OLZ. Whether this association reflects either reduced neurotoxicity or neuroprotection cannot be addressed with neuroimaging; changes may relate to glial rather than neural components. These maps revise current models of schizophrenia progression; due to power limitations, the findings require confirmation in a sample large enough to model group x time interactions.

Regional gray matter changes are associated with cognitive deficits in remitted geriatric depression: an optimized voxel-based morphometry study

BACKGROUND

We aimed to investigate structural abnormalities in first-episode remitted geriatric depression (RGD) with optimized voxel-based morphometry (VBM) in closely matched patients and healthy control subjects and examine the relationship of performances on neuropsychological tests with regional gray matter volumes.

METHODS

Nineteen subjects with first-episode RGD and 16 well-matched healthy control subjects were recruited for this study, and neuropsychological tests and magnetic resonance imaging were conducted on the subjects. The differences in regional gray matter volume were determined between these two groups by optimized VBM.

RESULTS

The volumes of right superior frontal cortex, left postcentral cortex, and right middle temporal gyrus were significantly smaller in patients with RGD relative to healthy control subjects. However, patients with RGD had larger left cingulate gyrus volume compared with healthy control subjects. There was a significant negative correlation between left cingulate gyrus volume and Rey Auditory Verbal Learning Test delayed recall raw score in patients with RGD.

CONCLUSION

These results reveal that RGD is associated with gray matter changes of certain brain regions hypothesized to influence cognition and might thus be involved in the psychopathology and pathophysiology of cognitive impairment in RGD.

Chronic administration of mood stabilizers upregulates BDNF and bcl-2 expression levels in rat frontal cortex

Brain-derived neurotrophic factor (BDNF) and B-cell lymphoma-2 (Bcl-2) proteins are neuroprotective factors involved in neuronal signaling, survival and plasticity. Both can be regulated by cyclic AMP response element binding (CREB) protein. Decreased levels of BDNF and Bcl-2 are implicated in the pathogenesis of bipolar disorder. The present study investigated whether chronically administered mood stabilizers would increase BDNF and/or Bcl-2 levels in rat brain. Real time RT-PCR, sandwich ELISA and Western blotting were used to measure BDNF and Bcl-2 mRNA and protein levels in the frontal cortex of rats chronically administered carbamazepine (CBZ) or lamotrigine (LTG) to produce plasma concentrations therapeutically relevant to bipolar disorder. Chronic CBZ and LTG significantly increased BDNF and Bcl-2 mRNA and protein levels in the frontal cortex. A common mechanism of action of mood stabilizers in the treatment of bipolar disorder may involve neuroprotection mediated by upregulation of brain BDNF and Bcl-2 expression.

Brain oscillatory responses in patients with bipolar disorder manic episode before and after valproate treatment

BACKGROUND

GABA/Glutamatergic dysfunction and neural circuits which regulate cognitive processing are involved in the underlying pathology of bipolar disorder. Event related oscillatory neuroelectrical activity reflects integrative brain functioning, different frequency bands representing different cognitive functions.

METHODS

Event Related Potentials to visual odd-ball paradigm in ten manic/hypomanic medication free, DSM-IV bipolar patients were measured before and after six weeks of valproate monotherapy in comparison to ten sex and age matched healthy controls. Different frequency band responses were obtained by digital filtration of ERPs. Young mania rating scale (YMRS) was used to assess clinical response. Repeated measures ANOVA, Wilcoxon and Mann Whitney U tests were used for statistical analysis.

RESULTS

Patients showed significantly higher baseline occipital beta (18-30 Hz) (p: 0.014) response than healthy controls. They were devoid of the occipito-frontal alpha (8-13 Hz) dominance presented by the control group. Occipital beta response reduced significantly (p: 0.009) and became similar to controls after treatment. Post-treatment alpha responses were significantly lower than baseline in anterior temporal (p: 0.038) and occipital (p: 0.027) locations. Healthy controls displayed a significantly increased frontal alpha response at the second assessment but the patients did not. Mean YMRS score reduced significantly compared to baseline at the end of six weeks (p: 0.004).

CONCLUSIONS

Alpha response is the universal operator in the brain. Increased occipital beta response in mania may be compensatory to the dysfunctional alpha operation. Its reduction after valproate may be through modulation of glutamatergic and GABAergic mechanisms and indicate medication's corrective effect on the underlying pathogenesis.

White matter abnormalities in bipolar disorder: a voxel-based diffusion tensor imaging study

OBJECTIVES

In bipolar disorder (BD), dysregulation of mood may result from white matter abnormalities that disrupt fronto-subcortical circuits. In this study, we explore such abnormalities using diffusion tensor imaging (DTI), an imaging technique capable of detecting subtle changes not visible with conventional magnetic resonance imaging (MRI), and voxel-based analysis.

METHODS

Thirty-six patients with BD, all but two receiving antidepressants or mood stabilizers, and 28 healthy controls matched for age and gender were studied. Diffusion-weighted echoplanar images (DW-EPI) were obtained using a 1.5T scanner. Voxel-based analysis was performed using SPM 2. Differences between the groups in mean diffusivity and fractional anisotropy (FA) were explored.

RESULTS

In the patient group, mean diffusivity was increased in the right posterior frontal and bilateral prefrontal white matter, while FA was decreased [corrected] in the inferior, middle temporal and middle occipital regions. The areas of increased mean diffusivity overlapped with those previously found to be abnormal using volumetric MRI and magnetization transfer imaging (MTI) in the same group of patients.

CONCLUSIONS

White matter abnormalities, predominantly in the fronto-temporal regions, can be detected in patients with BD using DTI. The neuropathology of these abnormalities is uncertain, but neuronal and axonal loss, myelin abnormalities and alterations in axonal packing density are likely to be relevant. The neuroprotective effects of some antidepressants and mood stabilizers make it unlikely that medication effects could explain the abnormalities described here, although minor effects cannot be excluded.

Assessing the role of cingulate cortex in bipolar disorder: neuropathological, structural and functional imaging data

OBJECTIVES

Most of the neuroanatomical models of bipolar disorder (BD) propose a key role for the anterior cingulate cortex (ACC). We provide here a review of currently available data regarding the CC neuroimaging and neuropathological alterations in BD.

MATERIALS AND METHODS

After an exploratory search of the MEDLINE, we first identified all English-written articles that provide separate data for BD patients and report original experimental data on cingulate gyrus. Subsequently, we selected those including neuroimaging or neuropathological data. Among the 161 articles updated through June 2007, 81 articles were retained using this procedure.

RESULTS

The review of in vivo volumetric imaging data, as well as ex vivo morphometric and histological studies indicates that BD patients show volume changes of the subgenual ACC (sgACC-BA 25 and part of 24) during the early stages of the disease. Whether this phenomenon is due to neuronal and glial depletion or damage of corticocortical connections is still a matter of debate. The resting state activity in the left BA 25 appears to be state dependent showing significant increase during mania and decrease during depressive phases. The presence of a deficient GABAergic activity in ACC is also documented. Pharmacological treatment partly restores BD-related functional imaging changes.

CONCLUSION

The present review reveals the striking discrepancies of the experimental results present both for functional and structural imaging studies but also for neuropathological analyses. Methodological and conceptual limitations are addressed with particular reference to the heterogeneity of BD clinical patterns. We also critically discuss the validity of CC changes as possible trait- or state-markers of the disease.

Anatomical abnormalities of the anterior cingulate and paracingulate cortex in patients with bipolar I disorder

Abnormalities of the anterior cingulate cortex (ACC) are thought to be involved in the pathophysiology of bipolar disorder, but structural Magnetic Resonance Imaging (MRI) studies have reported variable findings. Reasons for this include a failure to consider variability in regional cortical folding patterns and a reliance on relatively coarse measures (e.g., volume) to index anatomical change. We sought to overcome these limitations by combining a novel protocol for parcellating the ACC and adjacent paracingulate cortex (PaC) that accounts for inter-individual variations in sulcal and gyral morphology with a cortical surface-based approach that allowed calculation of regional grey matter volume, surface area and cortical thickness in 24 patients with bipolar I disorder and 24 matched controls. No changes in grey matter volume or surface area were identified in any region, but patients did show significant reductions in cortical thickness in the left rostral PaC and right dorsal PaC that were not attributable to group differences in cortical folding patterns. These findings suggest that bipolar disorder is associated with more pronounced changes in the PaC, and that reliance on volumetric measures alone may obscure more subtle differences.

Volumetric neuroimaging investigations in mood disorders: bipolar disorder versus major depressive disorder

BACKGROUND

As patients with mood disorders manifest heterogeneity in phenomenology, pathophysiology, etiology, and treatment response, a biological classification of mental disease is urgently needed to advance research. Patient and methodological variability complicates the comparison of neuroimaging study results and limits heuristic model development and a biologically-based diagnostic schema.

OBJECTIVE

We have critically reviewed and compared the magnetic resonance neuroimaging literature to determine the degree and directionality of volumetric changes in brain regions putatively implicated in the pathophysiology of major depressive disorder (MDD) versus bipolar disorder (BD).

METHODS

A total of 140 published magnetic resonance imaging investigations evaluating subjects with BD or MDD were selected to provide a summary and interpretation of volumetric neuroimaging results in MDD and BD. Further commentary on the pathophysiological implications, and putative cellular and pharmacological mechanisms, is also provided.

RESULTS

While whole brain volumes of patients with mood disorders do not differ from those of healthy controls, regional deficits in the frontal lobe, particularly in the anterior cingulate and the orbitofrontal cortex, appear to consistently differentiate subjects with mood disorders from the general population. Preliminary findings also suggest that subcortical structures, particularly the striatum, amygdala, and hippocampus, may be differentially affected in MDD and BD.

CONCLUSIONS

Structural neuroimaging studies have consistently identified regional abnormalities in subjects with mood disorders. Future studies should strive to definitively establish the influence of age and medication.

Neuropsychological correlates of homocysteine levels in euthymic bipolar patients

BACKGROUND

We have previously reported that homocysteine levels are elevated in euthymic bipolar patients with functional deterioration. The current study was designed to extend this finding by examining the relationship between neuropsychological functioning and homocysteine levels in euthymic bipolar patients.

METHODS

Fifty-seven euthymic bipolar outpatients were assessed for serum levels of homocysteine, folic acid, and vitamin B-12 and administered a battery of neuropsychological tests.

RESULTS

We found that male bipolar subjects showed higher average homocysteine levels than a comparison group of normal subjects, that poorer functioning on a task of executive function (Wisconsin Card Sort) was related to higher homocysteine levels, and that folic acid or vitamin B-12 levels did not significantly affect neuropsychological functioning.

LIMITATIONS

These results, while suggesting some relationship between higher homocysteine levels, bipolar illness, and impairment in cognitive function do not establish any causative effects.

CONCLUSIONS

The findings of this study confirm that in euthymic bipolar patients, higher homocysteine levels are associated with poorer performance in some neuropsychological tests. Treatment trials will be required before it will be known if the putative decrements in the executive function of bipolar patients can be reversed, or at least retarded, if homocysteine levels are reduced (as, for example, by dietary addition of B vitamin supplements).

Progressive gray matter loss in patients with bipolar disorder

BACKGROUND

Structural brain abnormalities of the medial temporal lobe have been found in people with bipolar disorder (BPD). It is not known whether these abnormalities progress over the course of the illness or how they relate to neuropsychologic functioning. We sought to address these uncertainties in a prospective cohort study of people with bipolar I disorder.

METHODS

Twenty patients with bipolar I disorder and 21 control subjects were recruited from the community. Participants were group matched for age, sex, and premorbid IQ. Longitudinal change in gray matter density was assessed using magnetic resonance imaging and evaluated using the technique of tensor-based morphometry with SPM2 software. Changes in gray and white matter density were estimated and compared with changes in cognitive function and clinical outcome.

RESULTS

Patients with BPD showed a larger decline in hippocampal, fusiform, and cerebellar gray matter density over 4 years than control subjects. No significant changes in white matter density were found. Reductions in temporal lobe gray matter correlated with decline in intellectual function and with the number of intervening mood episodes over the follow-up period.

CONCLUSIONS

Patients with BPD lose hippocampal, fusiform and cerebellar gray matter at an accelerated rate compared with healthy control subjects. This tissue loss is associated with deterioration in cognitive function and illness course.

Diagnostic validity of sensory over-responsivity: a review of the literature and case reports

Atypical responses to sensory stimulation are frequently reported to co-occur with diagnoses such as autism, ADHD, and Fragile-X syndrome. It has also been suggested that children and adults may present with atypical sensory responses while failing to meet the criteria for other medical or psychological diagnoses. This may be particularly true for individuals with over-responsivity to sensation. This article reviews the literature related to sensory over-responsivity and presents three pediatric cases that present a profile of having sensory over-responsivity without a co-occurring diagnosis. Findings from these cases provide very preliminary evidence to support the suggestion that sensory over-responsivity can occur as a sole diagnosis. Within this small group, tactile over-responsivity was the most common and pervasive form of this condition.

Relationship between regional brain metabolism, illness severity and age in depressed subjects

We sought to examine the effects of age, depression chronicity, and treatment responsiveness on glucose metabolism in a large well-characterized sample of depressed men and a psychiatrically unaffected control group. The subjects were unmedicated, symptomatic, right-handed males (n=66) who met DSM-IV criteria for a major depressive episode in the context of a major depressive disorder (MDD, n=66) and never depressed, right-handed, healthy control subjects (HC, n=24). Subjects in the MDD group were subsequently classified as responders, or non-responders to a six-week trial of paroxetine monotherapy (20-60 mg). Statistical parametric mapping (SPM) was used to analyze the relationship between age and cerebral glucose metabolism (18-fluorodeoxyglucose positron emission tomography) and the modulation by treatment responsivity and a history of prior depressive episodes. Metabolic activity in the rostral and dorsal anterior cingulate cortex showed a significant negative correlation with age in MDD, but not in HC. Non-response to treatment and previous depressive episodes were associated with a higher degree of age-dependent hypometabolism in the rostral and anterior cingulate cortex. The age-dependent changes documented herein may influence the distinct clinical presentation and treatment response described in older-age depression.

Applications for magnetic resonance imaging in bipolar disorder

Bipolar disorder is a prevalent psychiatric disorder with a high rate of misdiagnosis and evidence of degenerative progression. Research indicates that the interval between bipolar episodes decreases steadily until the patient settles into a relatively frequent course of mania and depression. Various imaging techniques have been used in the understanding of the brain pathology underlying bipolar disorder through identification of patterns consistent with disruption of the normal brain activity in bipolar patients. These techniques have demonstrated evidence of abnormalities in the structure and function of the prefrontal cortex. In addition, the cerebellar vermis, which serves as an error-detection function to modulate the iterative network, appears to shrink with recurrent episodes. Functional imaging demonstrates that the anterior limbic network is overactivated and overresponsive in patients with bipolar disorder. In many patients, those deficits are often compensated for by activation of other brain areas. Ultimately, when the compensation fails, expression of bipolar symptoms arise. Using magnetic resonance spectroscopy, simple models can be constructed based on the hypothesis that mitochondrial function may be impaired in bipolar disorder. There is also increasing evidence that psychotropic medications can affect specific brain regions that are thought to be involved in the pathogenesis of psychiatric disorders. Glutamate levels appear to be elevated in untreated patients with bipolar disorder, which may cause glutamatergic neurotoxicity and negative therapeutic implications. Further advances in brain imaging may contribute to the improvement of available therapies and the understanding which treatments will be most suitable for specific patients.

Increased risk of developing stroke among patients with bipolar disorder after an acute mood episode: a six-year follow-up study

BACKGROUND

Despite cerebrovascular diseases having been reported as one of the major causes of death among patients with bipolar disorder, there is scant information on the risk of stroke among this patient population. This study estimated the relative risk of developing stroke among patients with bipolar disorder in 6 years following hospitalization for an acute mood episode compared with patients undergoing appendectomy.

METHODS

Two study cohorts were identified from the Taiwan National Health Insurance Research Database for the year 1998: patients hospitalized with bipolar disorder, and patients undergoing an appendectomy. Follow-up was undertaken to determine whether sampled patients had utilized emergency medical services for the management of any type of stroke in the period 1998-2003.

RESULTS

Stroke occurred among 2.97% of patients with bipolar disorder and 1.50% of patients undergoing appendectomy between 1998 and 2003. The adjusted odds ratio of developing stroke, by cohort, shows that after adjusting for demographic characteristics, comorbid medical disorder, and substance or alcohol dependence, patients with bipolar disorder were more likely to develop stroke (OR=2.05; 95% CI=1.73-3.54).

LIMITATIONS

The validity of diagnoses, lacking of information on smoking, body mass index, and socioeconomic status, and possible selection bias might compromise the findings.

CONCLUSIONS

During the six-year follow-up period, the likelihood of developing stroke was twice as great amongst patients with bipolar disorder as patients undergoing an appendectomy. A requirement exists for the initiation of research providing an understanding of the pathophysiological mechanisms of the association between stroke and bipolar disorder.

Regional gray matter changes in bipolar disorder: a voxel-based morphometric study

OBJECTIVE

To investigate structural abnormalities in bipolar disorder (BD) using optimized voxel-based morphometry (VBM) in closely matched patients and controls, and to examine the relationship of clinical features with regional gray matter (GM) volumes.

METHODS

Twenty-four patients (six male) aged 19-59 years (mean=38.21 years, SD=11.04 years) with DSM-IV bipolar I disorder were compared with 25 control subjects, matched on age, sex, and years of education. VBM analyses were conducted on high-resolution T1-weighted brain magnetic resonance imaging to detect regional GM volume differences between groups, ensuring statistical correlation for age, sex and total intracranial volumes. Within the patient groups, regional GM changes were also investigated.

RESULTS

Compared to controls, BD patients had increased GM volume in left parahippocampal gyrus and decreased GM volume in left middle temporal gyrus. Family history, psychotic symptoms and lithium status were associated with regional GM abnormalities in BD patients.

CONCLUSIONS

This study presents evidence of gray matter volume abnormalities in adults with bipolar I disorder. Regional variation in relation to clinical factors suggests a neurobiological basis for clinical heterogeneity and posits the possibility of trait deficits.

Cortical sulci and bipolar disorder

The width of cortical sulci in bipolar patients (n=19) and healthy controls (n=35) was examined using a novel automated technique involving magnetic resonance imaging. All sulci were wider for bipolar patients than for healthy controls. Bipolar-control differences were largest for the superior and intermediate frontal sulci, smallest for the occipital and cingulate sulci, and intermediate in magnitude for the other sulci (intraparietal, inferior frontal, and central sulci). The results were interpreted in terms of neurodegenerative-illness-related processes, which could produce cortical atrophy and result in wider sulci.

Magnetic resonance-based morphometry: a window into structural plasticity of the brain

PURPOSE OF REVIEW

In contrast to traditional anatomical and pathological methods, magnetic resonance morphometry of the brain allows the in-vivo study of temporal changes in brain morphology and the correlation of brain morphology with brain function. Magnetic resonance morphometry has thereby recently emerged as one of the most promising fields in clinical neuroscience. This review covers the last 3 years, which have witnessed remarkable progress in this alluring new field.

RECENT FINDINGS

Next to the detection of structural differences in grey and white matter in a number of brain diseases, a very important recent finding of magnetic resonance-based morphometry is the discovery of the brain's ability to alter its shape within weeks, reflecting structural adaptation to physical and mental activity. Consequently, magnetic resonance morphometry promises to be a powerful method to study disease states of the brain and to track the effects of novel therapies.

SUMMARY

Despite these fascinating prospects, the results of morphometric studies are still dependent on the properties of the individual magnetic resonance scanner, which renders pooling of data almost impossible. It is also not known what the structural plasticity is based on at the histological or cellular level. Once these obstacles are overcome, magnetic resonance-based morphometry will become a powerful method for multicenter and therapeutic trials of several brain diseases.

Advances in magnetic resonance imaging methods for the evaluation of bipolar disorder

This article reviews the current state of magnetic resonance imaging techniques as applied to bipolar disorder. Addressed are conventional methods of structural neuroimaging and recently developed techniques. This latter group comprises volumetric analysis, voxel-based morphometry, the assessment of T2 white matter hyperintensities, shape analysis, cortical surface-based analysis, and diffusion tensor imaging. Structural analysis methods used in magnetic resonance imaging develop exponentially, and now present opportunities to identify disease-specific neuroanatomic alterations. Greater acuity and complementarity in measuring these alterations has led to the generation of further hypotheses regarding the pathophysiology of bipolar disorder. Included in the summary of findings is consideration of a resulting neuroanatomic model. Integrative issues and future directions in this relatively young field, including multi-modal approaches enabling us to produce more comprehensive results, are discussed.