Neuromodulation Strategies for the Treatment of Depression

Neuromodulation techniques in traumatic brain injury: a narrative review of the current state

Traumatic brain injury (TBI) is a leading cause of death and disability throughout the world. Despite significant advances in medical care, many TBI survivors continue to have cognitive, physical, and psychological deficits that have a significant impact on their quality of life. Neuromodulation techniques, which use electrical or magnetic stimulation to modulate brain activity, have shown promise in the treatment of TBI symptoms. The purpose of this narrative review is to provide an overview of the current state of neuromodulation techniques for TBI, such as transcranial magnetic stimulation, transcranial direct current stimulation, deep brain stimulation, and vagus nerve stimulation. This review summarizes the evidence for using these techniques, as well as their potential mechanisms of action and limitations. Additionally, the review discusses future research directions in this field, as well as the possibility of combining neuromodulation techniques with other interventions to improve outcomes for TBI patients.

40-Hz Temporally Interfering Electrical Stimulation Over the Temporal Lobe Induced Antidepressant-Like Effects in Chronic Unpredictable Mild Stress Rats

Temporally interfering (TI) electrical stimulation provides a promising noninvasive and focused stimulation for neuropsychiatric disorders. However, the feasible stimulation strategy and potential effects require further study. Our previous studies have identified gamma oscillatory abnormalities of temporal regions in depressed patients and rats. We accordingly aim to develop an effective TI antidepressant strategy. The stimulation strategy was firstly determined by modeling and simulation, and verified by c-Fos immunofluorescence staining. 32 rats were randomized into control (n = 8) and depression (n = 24) groups induced by chronic unpredictable mild stress (CUS), which were exposed to stimulation for 5 days, 20 mins per day. The behavioral and electrophysiology experiments were performed to examine the antidepressant-like effects of TI, using transcranial alternating current stimulation (tACS) as a positive control. In the electrophysiology experiment, local field potential (LFP) signals were recorded from bilateral primary auditory cortex (A1) before and after stimulation. We found that TI activated more c-Fos-positive cells in A1 target than tACS, exhibiting better stimulation focality. Both TI and tACS significantly ameliorated depression-like behaviors compared to sham group, and TI made more improvements. Furthermore, TI largely restored the gamma deficits by increasing gamma power and phase locking value (PLV) compared with tACS. And the gamma-band deficits were found remarkably correlated with depression-like behaviors. Overall, TI ameliorated depression-like behaviors in CUS rats, which may be associated with the restoration of aberrant gamma oscillations. With the advantages of both spatial targeting and noninvasive character, TI holds great promise for the clinical application of depression.

Neural Interoceptive Processing Is Modulated by Deep Brain Stimulation to Subcallosal Cingulate Cortex for Treatment-Resistant Depression

BACKGROUND

Symptoms of depression are associated with impaired interoceptive processing of bodily sensation. The antidepressant effects of subcallosal cingulate deep brain stimulation (SCC DBS) include acute change in bodily sensation, and the SCC target is connected to cortical regions critically involved in interoception. This study tested whether cortical interoceptive processing is modulated by SCC DBS for treatment-resistant depression.

METHODS

In 8 patients receiving SCC DBS for treatment-resistant depression, we used electroencephalography to measure the heartbeat-evoked potential (HEP), a putative readout of neural interoception, before surgery and over 6 months of treatment with DBS. We also examined the immediate effect of DBS on the HEP and correlated HEP change over time with outcomes of treatment for depression.

RESULTS

HEP amplitude increased from baseline to 6 months of DBS treatment, and this increase was associated with faster antidepressant response. Recording with stimulation on (vs. off) had an immediate effect on HEP in the laboratory. Overall, modulation of the HEP was most pronounced in sensors over the left parietal cortex.

CONCLUSIONS

Brain-based evidence implies an interoceptive element in the mechanism of treatment efficacy with DBS for treatment-resistant depression and substantiates a theorized connection between interoception and depression.

Altered synaptic homeostasis: a key factor in the pathophysiology of depression

Depression, a widespread psychiatric disorder, is characterized by a diverse array of symptoms such as melancholic mood and anhedonia, imposing a significant burden on both society and individuals. Despite extensive research into the neurobiological foundations of depression, a complete understanding of its complex mechanisms is yet to be attained, and targeted therapeutic interventions remain under development. Synaptic homeostasis, a compensatory feedback mechanism, involves neurons adjusting synaptic strength by regulating pre- or postsynaptic processes. Recent advancements in depression research reveal a crucial association between the disorder and disruptions in synaptic homeostasis within neural regions and circuits pivotal for emotional and cognitive functions. This paper explores the mechanisms governing synaptic homeostasis in depression, focusing on the role of ion channels, the regulation of presynaptic neurotransmitter release, synaptic scaling processes, and essential signaling molecules. By mapping new pathways in the study of synaptic homeostasis as it pertains to depression, this research aims to provide valuable insights for identifying novel therapeutic targets for more effective antidepressant treatments.

Striatal stimulation enhances cognitive control and evidence processing in rodents and humans

Brain disorders, in particular mental disorders, might be effectively treated by direct electrical brain stimulation, but clinical progress requires understanding of therapeutic mechanisms. Animal models have not helped, because there are no direct animal models of mental illness. Here, we propose a potential path past this roadblock, by leveraging a common ingredient of most mental disorders: impaired cognitive control. We previously showed that deep brain stimulation (DBS) improves cognitive control in humans. We now reverse translate that result using a set-shifting task in rats. DBS-like stimulation of the midstriatum improved reaction times without affecting accuracy, mirroring our human findings. Impulsivity, motivation, locomotor, and learning effects were ruled out through companion tasks and model-based analyses. To identify the specific cognitive processes affected, we applied reinforcement learning drift-diffusion modeling. This approach revealed that DBS-like stimulation enhanced evidence accumulation rates and lowered decision thresholds, improving domain-general cognitive control. Reanalysis of prior human data showed that the same mechanism applies in humans. This reverse/forward translational model could have near-term implications for clinical DBS practice and future trial design.

Comorbidity, Treatment, and Service Utilization Patterns in Difficult-to-Treat Depression Patients: A Retrospective Study in a Portuguese Community Mental Health Team

Background and Objectives: Observational studies with data from real-world clinical practice with patients with difficult-to-treat depression (DTD) are rare. This study aims to collect observational data from the real-world clinical practice of a Portuguese community mental health team (CMHT) on the prevalence of DTD and to explore differences between DTD and non-DTD groups. Materials and Methods: We conducted a retrospective chart review study using data from Electronic Health Records (EHRs) of adult patients with psychiatric disorders followed by a CMHT from the Department of Psychiatry of the Coimbra Local Health Unit (between 1 December 2020-31 December 2022). The Dutch Measure for quantification of Treatment Resistance in Depression (DM-TRD) was used to assess the degree of treatment resistance and the Charlson Comorbidity Index (CCI) to measure medical comorbidity. Results: A quantity of 473 patients were referred to Cantanhede CMHT for a first assessment. Of these, 219 patients met the criteria for a primary diagnosis of any depressive disorder. Assistant psychiatrists identified 57 patients with DTD during follow-up (approximately 26%). The DTD group had higher rates of depressive episodes, greater depression severity, increased service use, higher DM-TRD scores, and a higher prevalence of comorbid anxiety symptoms, personality disorders, and severe medical comorbidities. The DTD group also had a higher prescription rate of antidepressants. Differences were observed in the use of antidepressant augmentation strategies and in the prescription of anticoagulant/antiplatelet drugs and analgesics, with higher prescription rates in the DTD group. We found correlations between DM-TRD and CCI scores, and between DM-TRD scores and all service use variables. Conclusions: Our results are consistent with a similar study in the United Kingdom, highlighting the need for a different approach to the management of DTD patients, who continue to live with a significant burden despite usual pharmacological and non-pharmacological treatments.

Should rTMS be considered a first-line treatment for major depressive episodes in adults?

Treatment-resistant depression (TRD) is an epidemic with rising social, economic, and political costs. In a patient whose major depressive episode (MDE) persists through an adequate antidepressant trial, insurance companies often cover alternative treatments which may include repetitive transcranial magnetic stimulation (rTMS). RTMS is an FDA-cleared neuromodulation technique for TRD which is safe, efficacious, noninvasive, and well-tolerated. Recent developments in the optimization of rTMS algorithms and targeting have increased the efficacy of rTMS in treating depression, improved the clinical convenience of these treatments, and decreased the cost of a course of rTMS. In this opinion paper, we make a case for why conventional FDA-cleared rTMS should be considered as a first-line treatment for all adult MDEs. RTMS is compared to other first-line treatments including psychotherapy and SSRIs. These observations suggest that rTMS has similar efficacy, fewer side-effects, lower risk of serious adverse events, comparable compliance, the potential for more rapid relief, and cost-effectiveness. This suggestion, however, would be strengthened by further research with an emphasis on treatment-naive subjects in their first depressive episode, and trials directly contrasting rTMS with SSRIs or psychotherapy.

Magnetic resonance imaging connectivity features associated with response to transcranial magnetic stimulation in major depressive disorder

Transcranial magnetic stimulation (TMS) is an FDA-approved neuromodulation treatment for major depressive disorder (MDD), thought to work by altering dysfunctional brain connectivity pathways, or by indirectly modulating the activity of subcortical brain regions. Clinical response to TMS remains highly variable, highlighting the need for baseline predictors of response and for understanding brain changes associated with response. This systematic review examined brain connectivity features, and changes in connectivity features, associated with clinical improvement following TMS in MDD. Forty-one studies met inclusion criteria, including 1097 people with MDD. Most studies delivered one of two types of TMS to left dorsolateral prefrontal cortex and measured connectivity using resting-state functional MRI. The subgenual anterior cingulate cortex was the most well-studied brain region, particularly its connectivity with the TMS target or with the "executive control network" of brain regions. There was marked heterogeneity in findings. There is a need for greater understanding of how cortical TMS modulates connectivity with, and the activity of, subcortical regions, and how these effects change within and across treatment sessions.

The Advantages of Combining Therapies in Treating Psychiatric Patients

Mental illnesses are among the leading causes of morbidity and disability worldwide, and the burden associated with these disorders has increased steadily over the past three decades [...].

Novel rapid treatment options for adolescent depression

There is an urgent need for novel fast-acting antidepressants for adolescent treatment-resistant depression and/or suicidal risk, since the selective serotonin reuptake inhibitors that are clinically approved for that age (i.e., fluoxetine or escitalopram) take weeks to work. In this context, one of the main research lines of our group is to characterize at the preclinical level novel approaches for rapid-acting antidepressants for adolescence. The present review summarizes the potential use in adolescence of non-pharmacological options, such as neuromodulators (electroconvulsive therapy and other innovative types of brain stimulation), as well as pharmacological options, including consciousness-altering drugs (mainly ketamine but also classical psychedelics) and cannabinoids (i.e., cannabidiol), with promising fast-acting responses. Following a brief analytical explanation of adolescent depression, we present a general introduction for each therapeutical approach together with the clinical evidence supporting its potential beneficial use in adolescence (mainly extrapolated from prior successful examples for adults), to then report recent and/or ongoing preclinical studies that will aid in improving the inclusion of these therapies in the clinic, by considering potential sex-, age-, and dose-related differences, and/or other factors that might affect efficacy or long-term safety. Finally, we conclude the review by providing future avenues to maximize treatment response, including the need for more clinical studies and the importance of designing and/or testing novel treatment options that are safe and fast-acting for adolescent depression.

Happy Birthday "One Flew Over the Cuckoo's Nest": A Momentous Tale in the Quest for an Effective and Ethical Approach to Psychosurgery

The anniversary of the publication of 'One Flew Over the Cuckoo's Nest' by Ken Kesey offers an opportunity for reflection on the use of neurosurgery in psychiatry. We used a narrative, historical and dialectical method to deliver an account of the controversial subject. A balanced representation of the negative and positive aspects, acknowledging some of the questionable ethical practices while describing well-reasoned applications is provided. It includes neurosurgeons, psychiatrists who have embraced these procedures with unwarranted enthusiasm and those who have opposed. Neurosurgical techniques for the treatment of severe mental disorders have evolved from rudimentary procedures which were used to 'correct' unwanted behaviours associated with a wide range of severe mental disorders to more refined and selective approaches used as a last resort to treat specific mental health conditions. In the absence of specific aetiological models to guide ablative surgical targets, non-ablative, stimulatory techniques have more recently been developed to allow reversibility when surgical treatment fails to obtain a sizeable improvement in quality of life. The subject is concretely illustrated by two eloquent clinical images: one on a series of brain computed tomography scans carried out on a Canadian population of subjects, who underwent leukotomy decades ago, and the other more contemporary on an implantation surgery to epidural stimulation. Alongside technical advances in psychosurgery, a regulatory framework has gradually developed to ensure vigilance in the appropriateness of patients' selection. Nevertheless, harmonisation of protocols around the world is necessary to ensure consistency in obtaining and maintaining the highest possible ethical standards for the benefit of patients. If the neurosciences promise today, in their new, better framed, and reversible applications, to provide answers to unmet therapeutic needs, we still must remain attentive to drifts linked the introduction of intrusive technologies for purposes of domination or behaviour modification that would impede our individual freedom.

Transcutaneous cervical vagus nerve stimulation improved motor cortex excitability in healthy adults: a randomized, single-blind, self-crossover design study

Purpose

To investigate the effect of transcutaneous cervical vagus nerve stimulation (tcVNS) on motor cortex excitability in healthy adults.

Method

Twenty eight healthy subjects were assigned to receive real and sham tcVNS for 30 min. The interval between the real and sham conditions was more than 24 h, and the sequence was random. The central and peripheral motor-evoked potential (MEP) of the right first dorsal interosseous (FDI) muscle was measured by transcranial magnetic stimulation (TMS) before and after stimulation. MEP latency, MEP amplitude and rest motor threshold (rMT) were analyzed before and after stimulation.

Results

MEP amplitude, MEP latency and rMT had significant interaction effect between time points and conditions (p < 0.05). After real stimulation, the MEP amplitude was significantly increased (p < 0.001). MEP latency (p < 0.001) and rMT (p = 0.006) was decreased than that of baseline. The MEP amplitude on real condition was higher than that of sham stimulation after stimulation (p = 0.027). The latency after the real stimulation was significantly shorter than that after sham stimulation (p = 0.005). No significantly difference was found in rMT after stimulation between real and sham conditions (p > 0.05).

Conclusion

tcVNS could improve motor cortex excitability in healthy adults.

Pharmacotherapy for Treatment-Resistant Depression: Antidepressants and Atypical Antipsychotics

Treatment-resistant depression (TRD) affects one in three patients with major depressive disorder and is associated with increased risk of all-cause mortality. Studies of real-world practices suggest that antidepressant monotherapy continues to be the most widely used treatment after inadequate response to a first-line treatment. However, rates of remission with antidepressants in TRD are suboptimal. Atypical antipsychotics are the most widely studied augmentation agent and aripiprazole, brexpiprazole, cariprazine, quetiapine extended-release, and olanzapine-fluoxetine combination are approved for depression. Benefits of using atypical antipsychotics for TRD has to be weighted against their potential adverse events, such as weight gain, akathisia, and tardive dyskinesia.

Pharmacotherapies for Treatment-Resistant Depression: How Antipsychotics Fit in the Rapidly Evolving Therapeutic Landscape

One in three adults with major depressive disorder (MDD) do not experience clinically significant improvement after multiple sequential courses of antidepressants and have treatment-resistant depression (TRD). The presence of TRD contributes to the morbidity and excess mortality associated with MDD and has been linked to significantly increased health care expenses. In the absence of a consensus definition of TRD, this report takes a broad approach by considering inadequate response to one or more courses of antidepressants and focuses on atypical antipsychotics that are approved by the U.S. Food and Drug Administration for treatment of depression (aripiprazole, brexpiprazole, cariprazine, extended-release quetiapine, and olanzapine-fluoxetine combination). While multiple acute-phase studies have demonstrated the efficacy of these medications in improving depressive symptoms, clinically meaningful improvement (i.e., remission) remains limited, with significant concerns about side effects (including weight gain, metabolic dysfunction, extrapyramidal symptoms, and tardive dyskinesia), especially with long-term use. With the rapidly evolving landscape of antidepressant treatments over the past few years, which has witnessed approval of rapid-acting antidepressants (e.g., esketamine nasal spray and dextromethorphan-bupropion combination) and several more in the late-stage pipeline (e.g., zuranolone and psilocybin), it remains to be seen whether the use of atypical antipsychotics will go the way of the older and rarely prescribed antidepressants (such as tricyclics and monoamine oxidase inhibitors). Pragmatic clinical trials are needed to compare the effectiveness of atypical antipsychotics with TRD-specific pharmacotherapies and neuromodulation treatments and to identify the optimal sequencing of these varied approaches for patients with MDD. When using atypical antipsychotics, clinicians and patients are encouraged to use a shared decision-making approach by personalizing treatment selection based on anticipated side effects, tolerability, cost, and feasibility.

Are neuromodulation interventions associated with changes in the gut microbiota? A systematic review

The microbiota-gut-brain axis (MGBA) refers to the bidirectional communication between the brain and the gut microbiota and recent studies have linked the MGBA to health and disease. Research has so far investigated this axis mainly from microbiota to brain but less is known about the other direction. One approach to examine the MGBA from brain to microbiota is through understanding if and how neuromodulation might impact microbiota. Neuromodulation encompasses a wide range of stimulation techniques and is used to treat neurological, psychiatric and metabolic disorders, like Parkinson's Disease, depression and obesity. Here, we performed a systematic review to investigate whether neuromodulation is associated with subsequent changes in the gut microbiota. Searches in PsycINFO and MEDLINE were performed up to March 2022. Included studies needed to be clinical or preclinical studies comparing the effects of deep brain stimulation, electroconvulsive therapy, repetitive transcranial magnetic stimulation, transcranial direct current stimulation or vagal nerve stimulation on the gut microbiota before and after treatment or between active and control groups. Seven studies were identified. Neuromodulation was associated with changes in relative bacterial abundances, but not with (changes in) α-diversity or β-diversity. Summarizing, currently reported findings suggest that neuromodulation interventions are associated with moderate changes in the gut microbiome. However, findings remain inconclusive due to the limited number and varying quality of included studies, as well as the large heterogeneity between studies. More research is required to more conclusively establish whether, and if so, via which mechanism(s) of action neuromodulation interventions might influence the gut microbiota.

Neuroinflammation mechanisms of neuromodulation therapies for anxiety and depression

Mood disorders are associated with elevated inflammation, and the reduction of symptoms after multiple treatments is often accompanied by pro-inflammation restoration. A variety of neuromodulation techniques that regulate regional brain activities have been used to treat refractory mood disorders. However, their efficacy varies from person to person and lack reliable indicator. This review summarizes clinical and animal studies on inflammation in neural circuits related to anxiety and depression and the evidence that neuromodulation therapies regulate neuroinflammation in the treatment of neurological diseases. Neuromodulation therapies, including transcranial magnetic stimulation (TMS), transcranial electrical stimulation (TES), electroconvulsive therapy (ECT), photobiomodulation (PBM), transcranial ultrasound stimulation (TUS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS), all have been reported to attenuate neuroinflammation and reduce the release of pro-inflammatory factors, which may be one of the reasons for mood improvement. This review provides a better understanding of the effective mechanism of neuromodulation therapies and indicates that inflammatory biomarkers may serve as a reference for the assessment of pathological conditions and treatment options in anxiety and depression.

Attenuated interoceptive processing in individuals with major depressive disorder and high repetitive negative thinking

Repetitive negative thinking (RNT) is a transdiagnostic symptom associated with poor outcomes in major depressive disorder (MDD). MDD is characterized by altered interoception, which has also been associated with poor outcomes. The present study investigated whether RNT is directly associated with altered interoceptive processing. Interoceptive awareness toward the heart and stomach was probed on the Visceral Interoceptive Attention (VIA) task with fMRI in MDD individuals who were propensity-matched on the severity of depression and anxiety symptoms and relevant demographics but different in RNT intensity (High RNT [H-RNT, n = 48] & Low RNT [L-RNT, n = 49]), and in matched healthy volunteers (HC, n = 27). Both H-RNT and L-RNT MDD individuals revealed reduced stomach interoceptive processing compared to HC in the left medial frontal region and insular cortex (H-RNT: β = -1.04, L-RNT: β = -0.97), perirhinal cortex (H-RNT: β = -0.99, L-RNT: β = -1.03), and caudate nucleus (H-RNT: β = -1.06, L-RNT: β = -0.89). However, H-RNT was associated with decreased right medial temporal lobe activity including the hippocampus and amygdala during stomach interoceptive trials (β = -0.61) compared to L-RNT. Insular interoceptive processing was similar in H-RNT and L-RNT participants (β = -0.07, p = 0.92). MDD individuals with high RNT exhibited altered gastric interoceptive responses in brain areas that are important for associating the information with specific contexts and emotions. Attenuated interoceptive processing may contribute to RNT generation, non-adaptive information processing, action selection, and thus poor treatment outcome.

Recent innovations in non-invasive brain stimulation (NIBS) for the treatment of unipolar and bipolar depression: a narrative review

Depression, either bipolar or unipolar, is a highly prevalent and disabling condition. Even though several treatment options exist for depressed patients, a significant portion of individuals receiving conventional pharmacotherapy fails to achieve and sustain remission. For this reason, there is a strong need for effective alternatives to pharmacotherapy. In this respect, non-invasive brain stimulation (NIBS), including transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have been increasingly investigated in the last two decade as promising treatment strategies for major depression and treatment-resistant depression (TRD). Indeed, due to their safety and tolerability and to the growing evidence on their efficacy, NIBS has been included in international treatment guidelines, having become part of the standard clinical practice. Even though several clinical trials involving NIBS in patients with major depression and TRD have been conducted, literature in specific areas is still marked by some inconsistencies, due to small sample-sizes, lack of multicentre-studies and to the difficulty in comparing different treatment modalities and stimulation protocols. In light of the above, we sought to provide a brief, updated compendium of the latest innovative acquisition for the use of NIBS in the treatment of depression, either unipolar or bipolar, as well as TRD with a specific focus on innovative set-up, devices, target areas, and parameters that may affect the outcome.