Deep brain stimulation for bipolar disorder-review and outlook

Anti-manic effect of deep brain stimulation of the ventral tegmental area in an animal model of mania induced by methamphetamine

BACKGROUND

Treatment of refractory bipolar disorder (BD) is extremely challenging. Deep brain stimulation (DBS) holds promise as an effective treatment intervention. However, we still understand very little about the mechanisms of DBS and its application on BD.

AIM

The present study aimed to investigate the behavioural and neurochemical effects of ventral tegmental area (VTA) DBS in an animal model of mania induced by methamphetamine (m-amph).

METHODS

Wistar rats were given 14 days of m-amph injections, and on the last day, animals were submitted to 20 min of VTA DBS in two different patterns: intermittent low-frequency stimulation (LFS) or continuous high-frequency stimulation (HFS). Immediately after DBS, manic-like behaviour and nucleus accumbens (NAc) phasic dopamine (DA) release were evaluated in different groups of animals through open-field tests and fast-scan cyclic voltammetry. Levels of NAc dopaminergic markers were evaluated by immunohistochemistry.

RESULTS

M-amph induced hyperlocomotion in the animals and both DBS parameters reversed this alteration. M-amph increased DA reuptake time post-sham compared to baseline levels, and both LFS and HFS were able to block this alteration. LFS was also able to reduce phasic DA release when compared to baseline. LFS was able to increase dopamine transporter (DAT) expression in the NAc.

CONCLUSION

These results demonstrate that both VTA LFS and HFS DBS exert anti-manic effects and modulation of DA dynamics in the NAc. More specifically the increase in DA reuptake driven by increased DAT expression may serve as a potential mechanism by which VTA DBS exerts its anti-manic effects.

Bipolar mania and epilepsy pathophysiology and treatment may converge in purine metabolism: A new perspective on available evidence

Decreased ATPergic signaling is an increasingly recognized pathophysiology in bipolar mania disease models. In parallel, adenosine deficit is increasingly recognized in epilepsy pathophysiology. Under-recognized ATP and/or adenosine-increasing mechanisms of several antimanic and antiseizure therapies including lithium, valproate, carbamazepine, and ECT suggest a fundamental pathogenic role of adenosine deficit in bipolar mania to match the established role of adenosine deficit in epilepsy. The depletion of adenosine-derivatives within the purine cycle is expected to result in a compensatory increase in oxopurines (uric acid precursors) and secondarily increased uric acid, observed in both bipolar mania and epilepsy. Cortisol-based inhibition of purine conversion to adenosine-derivatives may be reflected in observed uric acid increases and the well-established contribution of cortisol to both bipolar mania and epilepsy pathology. Cortisol-inhibited conversion from IMP to AMP as precursor of both ATP and adenosine may represent a mechanism for treatment resistance common in both bipolar mania and epilepsy. Anti-cortisol therapies may therefore augment other treatments both in bipolar mania and epilepsy. Evidence linking (i) adenosine deficit with a decreased need for sleep, (ii) IMP/cGMP excess with compulsive hypersexuality, and (iii) guanosine excess with grandiose delusions may converge to suggest a novel theory of bipolar mania as a condition characterized by disrupted purine metabolism. The potential for disease-modification and prevention related to adenosine-mediated epigenetic changes in epilepsy may be mirrored in mania. Evaluating the purinergic effects of existing agents and validating purine dysregulation may improve diagnosis and treatment in bipolar mania and epilepsy and provide specific targets for drug development.

Anatomical characterisation of three different psychosurgical targets in the subthalamic area: from the basal ganglia to the limbic system

Effective neural stimulation for the treatment of severe psychiatric disorders needs accurate characterisation of surgical targets. This is especially true for the medial subthalamic region (MSR) which contains three targets: the anteromedial STN for obsessive compulsive disorder (OCD), the medial forebrain bundle (MFB) for depression and OCD, and the "Sano triangle" for pathological aggressiveness. Blocks containing the subthalamic area were obtained from two human brains. After obtaining 11.7-Tesla MRI, blocks were cut in regular sections for immunohistochemistry. Fluorescent in situ hybridisation was performed on the macaque MSR. Electron microscopic observation for synaptic specialisation was performed on human and macaque subthalamic fresh samples. Images of human brain sections were reconstructed in a cryoblock which was registered on the MRI and histological slices were then registered. The STN contains glutamatergic and fewer GABAergic neurons and has no strict boundary with the adjacent MSR. The anteromedial STN has abundant dopaminergic and serotoninergic innervation with very sparse dopaminergic neurons. The MFB is composed of dense anterior dopaminergic and posterior serotoninergic fibres, and fewer cholinergic and glutamatergic fibres. Medially, the Sano triangle presumably contains orexinergic terminals from the hypothalamus, and neurons with strong nuclear oestrogen receptor-alpha staining with a decreased anteroposterior and mediolateral gradient of staining. These findings provide new insight regarding MSR cells and their fibre specialisation, forming a transition zone between the basal ganglia and the limbic systems. Our 3D reconstruction enabled us to visualize the main histological features of the three targets which should enable better targeting and understanding of neuromodulatory stimulation results in severe psychiatric conditions.

Diagnosis and management of bipolar disorders

Bipolar disorders (BDs) are recurrent and sometimes chronic disorders of mood that affect around 2% of the world's population and encompass a spectrum between severe elevated and excitable mood states (mania) to the dysphoria, low energy, and despondency of depressive episodes. The illness commonly starts in young adults and is a leading cause of disability and premature mortality. The clinical manifestations of bipolar disorder can be markedly varied between and within individuals across their lifespan. Early diagnosis is challenging and misdiagnoses are frequent, potentially resulting in missed early intervention and increasing the risk of iatrogenic harm. Over 15 approved treatments exist for the various phases of bipolar disorder, but outcomes are often suboptimal owing to insufficient efficacy, side effects, or lack of availability. Lithium, the first approved treatment for bipolar disorder, continues to be the most effective drug overall, although full remission is only seen in a subset of patients. Newer atypical antipsychotics are increasingly being found to be effective in the treatment of bipolar depression; however, their long term tolerability and safety are uncertain. For many with bipolar disorder, combination therapy and adjunctive psychotherapy might be necessary to treat symptoms across different phases of illness. Several classes of medications exist for treating bipolar disorder but predicting which medication is likely to be most effective or tolerable is not yet possible. As pathophysiological insights into the causes of bipolar disorders are revealed, a new era of targeted treatments aimed at causal mechanisms, be they pharmacological or psychosocial, will hopefully be developed. For the time being, however, clinical judgment, shared decision making, and empirical follow-up remain essential elements of clinical care. This review provides an overview of the clinical features, diagnostic subtypes, and major treatment modalities available to treat people with bipolar disorder, highlighting recent advances and ongoing therapeutic challenges.

Brain stimulation treatment for bipolar disorder

AIMS

Bipolar disorders are clinically complex, chronic and recurrent disorders. Few treatment options are effective across hypomanic, manic, depressive and mixed states and as continuation or maintenance treatment after initial symptom remission. The aim of this review was to provide an up-to-date overview of research on the efficacy, tolerability and cognitive effects of electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), magnetic seizure therapy (MST), deep brain stimulation (DBS) and vagus nerve stimulation (VNS).

METHODS

References included in this review were identified through multiple searches of the Embase, PubMed/MEDLINE and APA PsycINFO electronic databases for articles published from inception until February 2022. Published reviews, meta-analyses, randomised controlled trials and recent studies were prioritised to provide a comprehensive and up-to-date overview of research on brain stimulation in patients with bipolar disorders.

RESULTS

The evidence base for brain stimulation as an add-on or alternative to pharmacological and psychological treatments in patients with bipolar disorders is limited but rapidly expanding. Brain stimulation treatments represent an opportunity to treat all bipolar disorder states, including cognitive dysfunction during euthymic periods.

CONCLUSION

Whilst findings to date have been encouraging, larger randomised controlled trials with long-term follow-up are needed to clarify important questions regarding treatment efficacy and tolerability, the frequency of treatment-emergent affective switches and effects on cognitive function.

Recent advances in psychoradiology

Psychiatry, as a field, lacks objective markers for diagnosis, progression, treatment planning, and prognosis, in part due to difficulties studying the brain in vivo, and diagnoses are based on self-reported symptoms and observation of patient behavior and cognition. Rapid advances in brain imaging techniques allow clinical investigators to noninvasively quantify brain features at the structural, functional, and molecular levels. Psychoradiology is an emerging discipline at the intersection of psychiatry and radiology. Psychoradiology applies medical imaging technologies to psychiatry and promises not only to improve insight into structural and functional brain abnormalities in patients with psychiatric disorders but also to have potential clinical utility. We searched for representative studies related to recent advances in psychoradiology through May 1, 2022, and conducted a selective review of 165 references, including 75 research articles. We summarize the novel dynamic imaging processing methods to model brain networks and present imaging genetics studies that reveal the relationship between various neuroimaging endophenotypes and genetic markers in psychiatric disorders. Furthermore, we survey recent advances in psychoradiology, with a focus on future psychiatric diagnostic approaches with dimensional analysis and a shift from group-level to individualized analysis. Finally, we examine the application of machine learning in psychoradiology studies and the potential of a novel option for brain stimulation treatment based on psychoradiological findings in precision medicine. Here, we provide a summary of recent advances in psychoradiology research, and we hope this review will help guide the practice of psychoradiology in the scientific and clinical fields.

Diving into the Subcortex: The Potential of Chronic Subcortical Sensing for Unravelling Basal Ganglia Function and Optimization of Deep Brain STIMULATION

Subcortical structures are a relative neurophysiological 'terra incognita' owing to their location within the skull. While perioperative subcortical sensing has been performed for more than 20 years, the neurophysiology of the basal ganglia in the home setting has remained almost unexplored. However, with the recent advent of implantable pulse generators (IPG) that are able to record neural activity, the opportunity to chronically record local field potentials (LFPs) directly from electrodes implanted for deep brain stimulation opens up. This allows for a breakthrough of chronic subcortical sensing into fundamental research and clinical practice. In this review an extensive overview of the current state of subcortical sensing is provided. The widespread potential of chronic subcortical sensing for investigational and clinical use is discussed. Finally, status and future perspectives of the most promising application of chronic subcortical sensing -i.e., adaptive deep brain stimulation (aDBS)- are discussed in the context of movement disorders. The development of aDBS based on both chronic subcortical and cortical sensing has the potential to dramatically change clinical practice and the life of patients with movement disorders. However, several barriers still stand in the way of clinical implementation. Advancements regarding IPG and lead technology, physiomarkers, and aDBS algorithms as well as harnessing artificial intelligence, multimodality and sensing in the naturalistic setting are needed to bring aDBS to clinical practice.

DTI for brain targeting: Diffusion weighted imaging fiber tractography-Assisted deep brain stimulation

Fiber tractography assisted Deep Brain Stimulation (DBS) has been performed by different groups for more than 10 years to now. Groups around the world have adapted initial approaches to currently embrace the fiber tractography technology mainly for treating tremor (DBS and lesions), psychiatric indications (OCD and major depression) and pain (DBS). Despite the advantages of directly visualizing the target structure, the technology is demanding and is vulnerable to inaccuracies especially since it is performed on individual level. In this contribution, we will focus on tremor and psychiatric indications, and will show future applications of sophisticated tractography applications for subthalamic nucleus (STN) DBS surgery and stimulation steering as an example.

New Frontiers for Deep Brain Stimulation: Directionality, Sensing Technologies, Remote Programming, Robotic Stereotactic Assistance, Asleep Procedures, and Connectomics

Over the last few years, while expanding its clinical indications from movement disorders to epilepsy and psychiatry, the field of deep brain stimulation (DBS) has seen significant innovations. Hardware developments have introduced directional leads to stimulate specific brain targets and sensing electrodes to determine optimal settings via feedback from local field potentials. In addition, variable-frequency stimulation and asynchronous high-frequency pulse trains have introduced new programming paradigms to efficiently desynchronize pathological neural circuitry and regulate dysfunctional brain networks not responsive to conventional settings. Overall, these innovations have provided clinicians with more anatomically accurate programming and closed-looped feedback to identify optimal strategies for neuromodulation. Simultaneously, software developments have simplified programming algorithms, introduced platforms for DBS remote management via telemedicine, and tools for estimating the volume of tissue activated within and outside the DBS targets. Finally, the surgical accuracy has improved thanks to intraoperative magnetic resonance or computerized tomography guidance, network-based imaging for DBS planning and targeting, and robotic-assisted surgery for ultra-accurate, millimetric lead placement. These technological and imaging advances have collectively optimized DBS outcomes and allowed “asleep” DBS procedures. Still, the short- and long-term outcomes of different implantable devices, surgical techniques, and asleep vs. awake procedures remain to be clarified. This expert review summarizes and critically discusses these recent innovations and their potential impact on the DBS field.

Treatment-resistant bipolar depression: concepts and challenges for novel interventions

Treatment-resistant bipolar depression (TRBD) has been reported in about one-quarter of patients with bipolar disorders, and few interventions have shown clear and established effectiveness. We conducted a narrative review of the published medical literature to identify papers discussing treatment-resistant depression concepts and novel interventions for bipolar depression that focus on TRBD. We searched for potentially relevant English-language articles published in the last decade. Selected articles (based on the title and abstract) were retrieved for a more detailed evaluation. A number of promising new interventions, both pharmacological and non-pharmacological, are being investigated for TRBD treatment, including ketamine, lurasidone, D-cycloserine, pioglitazone, N-acetylcysteine, angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, cyclooxygenase 2 inhibitors, magnetic seizure therapy, intermittent theta-burst stimulation, deep transcranial magnetic stimulation, vagus nerve stimulation therapy, and deep brain stimulation. Although there is no consensus about the concept of TRBD, better clarification of the neurobiology associated with treatment non-response could help identify novel strategies. More research is warranted, mainly focusing on personalizing current treatments to optimize response and remission rates.

Prevention of suicidal behavior in bipolar disorder

BACKGROUND

Excess mortality is a critical hallmark of bipolar disorder (BD) due to co-occurring general medical disorders and especially from suicide. It is timely to review of the status of suicide in BD and to consider the possibility of limiting suicidal risk.

METHODS

We carried out a semi-systematic review of recent research reports pertaining to suicide in BD.

FINDINGS

Suicide risk in BD is greater than with most other psychiatric disorders. Suicide rates (per 100,000/year) are approximately 11 and 4 in the adult and juvenile general populations, but over 200 in adults, and 100 among juveniles diagnosed with BD. Suicide attempt rates with BD are at least 20 times higher than in the adult general population, and over 50 times higher among juveniles. Notable suicidal risk factors in BD include: previous suicidal acts, depression, mixed-agitated-dysphoric moods, rapid mood-shifts, impulsivity, and co-occurring substance abuse. Suicide-preventing therapeutics for BD remain severely underdeveloped. Evidence favoring lithium treatment is stronger than for other measures, although encouraging findings are emerging for other treatments.

CONCLUSIONS

Suicide is a leading clinical challenge for those caring for BD patients. Improved understanding of risk and protective factors combined with knowledge and close follow-up of BD patients should limit suicidal risk. Ethically appropriate and scientifically sound studies of plausible medicinal, physical, and psychosocial treatments aimed at suicide prevention specifically for BD patients are urgently needed.

Deep brain stimulation: current challenges and future directions

The clinical use of deep brain stimulation (DBS) is among the most important advances in the clinical neurosciences in the past two decades. As a surgical tool, DBS can directly measure pathological brain activity and can deliver adjustable stimulation for therapeutic effect in neurological and psychiatric disorders correlated with dysfunctional circuitry. The development of DBS has opened new opportunities to access and interrogate malfunctioning brain circuits and to test the therapeutic potential of regulating the output of these circuits in a broad range of disorders. Despite the success and rapid adoption of DBS, crucial questions remain, including which brain areas should be targeted and in which patients. This Review considers how DBS has facilitated advances in our understanding of how circuit malfunction can lead to brain disorders and outlines the key unmet challenges and future directions in the DBS field. Determining the next steps in DBS science will help to define the future role of this technology in the development of novel therapeutics for the most challenging disorders affecting the human brain.

Transcending the brain: is there a cost to hacking the nervous system?

Great advancements have recently been made to understand the brain and the potential that we can extract out of it. Much of this has been centred on modifying electrical activity of the nervous system for improved physical and cognitive performance in those with clinical impairment. However, there is a risk of going beyond purely physiological performance improvements and striving for human enhancement beyond traditional human limits. Simple ethical guidelines and legal doctrine must be examined to keep ahead of technological advancement in light of the impending mergence between biology and machine. By understanding the role of modern ethics, this review aims to appreciate the fine boundary between what is considered ethically justified for current neurotechnology.

Microelectrode array electrical impedance tomography for fast functional imaging in the thalamus

Electrical Impedance Tomography (EIT) has the potential to be able to observe functional tomographic images of neural activity in the brain at millisecond time-scales. Prior modelling and experimental work has shown that EIT is capable of imaging impedance changes from neural depolarisation in rat somatosensory cortex. Here, we investigate the feasibility of EIT for imaging impedance changes using a stereotaxically implanted microelectrode array in the thalamus. Microelectrode array EIT was simulated using an anatomically accurate marmoset brain model. Impedance imaging was validated and detectability estimated using physiological noise recorded from the marmoset visual thalamus. The results suggest that visual-input-driven impedance changes in visual subcortical bodies within 300 μm of the implanted array could be reliably reconstructed and localised, comparable to local field potential measurements. Furthermore, we demonstrated that microelectrode array EIT could reconstruct concurrent activity in multiple subcortical bodies simultaneously.

Recent advances in deep brain stimulation in psychiatric disorders

Deep brain stimulation (DBS) has been offered to patients suffering of severe and resistant neuropsychiatric disorders like Obsessive Compulsive Disorder (OCD), Gilles de la Tourette Syndrome (TS) and Major Depression (MDD). Modulation of several targets within the cortico-striato-thalamo-cortical circuits can lead to a decrease of symptom severity in those patients. This review focuses on the recent clinical outcomes in DBS in psychiatric disorders. Studies on OCD and TS are now focusing on the long-term effects of DBS, with encouraging results regarding not only the decrease of symptoms, but also quality of life. They also highlighted efficient adjuvant techniques, like cognitive and behavioural therapy and support programs, to enhance an often-partial response to DBS. The application of DBS for MDD is more recent and, despite encouraging initial open-label studies, two large randomised studies have failed to demonstrate an efficacy of DBS in MDD according to evidence-based medicine criteria. Last years, DBS was also tested in other resistant psychiatric disorders, as anorexia nervosa and addiction, with encouraging preliminary results. However, today, no target – whatever the disease – can meet the criteria for clinical efficacy as recently defined by an international committee for neurosurgery for psychiatric disorders. Consequently, DBS in psychiatric disorders still needs to proceed within the frame of clinical trials.

The application of deep brain stimulation in the treatment of psychiatric disorders

Deep brain stimulation (DBS) is a last-resort treatment for neurological and psychiatric disorders that are refractory to standard treatment. Over the last decades, the progress of DBS in psychiatry has been slower than in neurology, in part owing to the heterogenic symptomatology and complex neuroanatomy of psychiatric disorders. However, for obsessive-compulsive disorder (OCD) DBS is now an accepted treatment. This study first reviews clinical outcomes and mechanisms of DBS for OCD, and then discusses these results in an overview of current and future psychiatric applications, including DBS for mood disorders, Tourette's syndrome, addiction, anorexia nervosa, autism, schizophrenia, and anxiety disorders. In addition, it will focus on novel techniques that may enhance the application of DBS in psychiatry.