Neuromodulation in psychiatric disorders

Differential patterns of executive dysfunction across depressive phenotype in schizophrenia and major depressive disorder

Executive functioning (EF) deficits are common in both schizophrenia (SZ) and major depressive disorder (MDD). However, it remains unclear whether specific EF subdomains are differently affected in SZ and MDD, particularly in relation to depressive symptoms. This study aims to investigate EF subdomains in MDD, SZ with depressive symptoms (SZ-D), SZ without depressive symptoms (SZ-ND) and healthy controls (HC), and to explore the relationships between psychopathological symptoms and EF performance. A total of 213 participants were recruited, including 76 MDD, 81 SZ patients and 56 HC. EF was assessed using the n-back, Stroop color-word and more-odd shifting tasks. The 17-item Hamilton Depression Scale, Hamilton Anxiety Scale and Positive and Negative Syndrome Scale were used to assess depression, anxiety and psychopathological symptoms. In the 2-back task, SZ-D patients had longer response time (RT) (p < 0.01), while SZ-ND patients had lower accuracy rates (AR) (p < 0.01) compared to MDD patients and HC. In more-odd shifting task, SZ-D patients showed longer RT for shift cost (p < 0.01), and SZ-ND patients had lower AR for shift cost (p < 0.01) compared to MDD and HC. Multiple regression analysis revealed that negative symptoms were associated with AR in the 2-back condition in SZ-D, while in SZ-ND, negative symptoms was related to AR in the 1-back condition. SZ patients showed more severe EF dysfunction, with depressive symptoms in SZ primarily affecting response speed rather than accuracy. Negative symptoms were associated with EF dysfunction in both MDD and SZ patients.

A Two-Way Communication Between Apical Periodontitis and Various Systemic Disorders: A Narrative Review

One prevalent inflammatory disorder that affects the mouth is apical periodontitis. It starts with an infection in the tooth's pulp chamber. The periapical bone may eventually deteriorate as a result of this infection spreading there. Systemic immune responses are triggered when inflammatory cytokines generated in periapical lesions and pathogens and their metabolites in the periapical tissues enter the bloodstream. Numerous systemic disorders may emerge as a result of this procedure. Although endodontic infections can be influenced by systemic disorders, there is ample evidence that these infections can also result in bodily changes that impair general health. Therefore, rather than being a limited oral problem, apical periodontitis may be associated with systemic illnesses. Furthermore, individuals with chronic inflammation-related diseases may experience hyperinflammatory states, which could influence the progression or outcome of apical periodontitis. The underlying mechanisms and the relationship between apical periodontitis and systemic diseases are still unknown. Even though this topic has been explored previously, new information has just come to light. This review's objective is to evaluate the body of knowledge regarding the evolving relationships between endodontic therapy, apical periodontitis, and systemic health. Gaining a better understanding of this relationship will help medical professionals identify risk factors and enhance the recovery of apical periodontitis and systemic illnesses.

Intracranial closed-loop neuromodulation as an intervention for neuropsychiatric disorders: an overview

Recent technological advances in intracranial brain stimulation have enhanced the potential of neuromodulation for addressing neuropsychiatric disorders. We present a review of the methodology and the preliminary outcomes of the pioneering studies exploring intracranial biomarker detection and closed-loop neuromodulation to modulate high-symptom severity states in neuropsychiatric disorders. We searched PubMed, Scopus, Web of Science, Embase, and PsycINFO/PsycNet, followed by the reference and citation lists of retrieved articles. This search strategy yielded a total of 583 articles, of which 5 articles met the inclusion criteria, focusing on depression, obsessive-compulsive disorder, post-traumatic stress disorder, and binge eating disorder. We discuss the methodology of biomarker identification, the biomarkers identified, and the preliminary treatment outcomes for closed-loop neuromodulation. Successful biomarker identification hinges on investigating across various setting. Targeted neuromodulation, either directed at the biomarker or within its associated neural network, offers a promising treatment approach. Future research should seek to understand the mechanisms underlying the effects of neuromodulation as well as the long-term viability of these treatment effects across different neuropsychiatric conditions.

Defects of parvalbumin-positive interneurons are implicated in psychiatric disorders

Psychiatric disorders are a common cause of severe long-term disability and socioeconomic burden worldwide. Although our understanding of these disorders has advanced substantially over the last few years, little has changed the standards of care for these illnesses. Fast-spiking parvalbumin-positive interneurons (PVIs), a subpopulation of gamma-aminobutyric acid (GABA)ergic interneurons, are widely distributed in the hippocampus and have been reported to play an important role in various mental disorders. However, the mechanisms underlying the regulation of the molecular networks relevant to depression and schizophrenia (SCZ) are unknown. Here, we discuss the functions of PVIs in psychiatric disorders, including depression and SCZ. After reviewing several studies, we concluded that dysfunction in PVIs could cause depression-like behavior, as well as cognitive categories in SCZ, which might be mediated in large part by greater synaptic variability. In summary, this scientific review aims to discuss the current knowledge regarding the function of PVIs in depression and SCZ. Moreover, we highlight the importance of neurogenesis and synaptic plasticity in the pathogenesis of depression and SCZ, which seem to be mediated by PVIs activity. These findings provide a better understanding of the role of PVIs in psychiatric disorders.

Use of Antibacterial Envelopes in Neuromodulation Surgeries With Implantable Device Insertion: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Neuromodulation is an advanced therapeutic intervention for managing various neurological, psychiatric, and functional disorders. However, a significant challenge is the risk of infections at the device implantation site. Previous studies have shown that antibacterial envelopes used in cardiovascular surgeries significantly reduce infection risk. It is postulated that similar benefits could occur in neurosurgeries involving implant insertion, but the literature lacks studies analyzing this efficacy. This study aimed to evaluate the effectiveness of antibacterial envelopes in reducing infection rates associated with neuromodulation implants.

METHODS

We systematically searched PubMed, Embase, and the Cochrane Central Register of Controlled Trials databases up to August 2024 for clinical trials comparing the use of antibacterial impregnated envelopes in patients undergoing neuromodulation-related implant insertion. This study followed Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Statistical analyses were performed using R version 4.3.2. Risk of bias was assessed using the Risk Of Bias In Nonrandomized Studies-of Interventions tool, and the quality of evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation assessment. The study was registered in Prospective Register of Systematic Reviews.

RESULTS

Four studies, comprising 1242 patients, were included, of whom 704 (56.7%) received antibacterial envelopes. The pooled analysis showed that the odds of infection were 77% lower in patients using the antibacterial envelope compared with the control group (odds ratios = 0.23; 95% CI = 0.10-0.51; P < .001; I2 = 2%).

CONCLUSION

The use of an antibacterial envelope significantly reduces the odds of infection in patients undergoing neuromodulation-related implant insertion by 77%. These findings underscore the potential of antibacterial envelopes to improve postoperative outcomes.

The Association and Prognostic Implications of Long Non-Coding RNAs in Major Psychiatric Disorders, Alzheimer's Diseases and Parkinson's Diseases: A Systematic Review

The prevalence of psychiatric disorders and neurodegenerative diseases is steadily increasing, placing a significant burden on both society and individuals. Given the intricate and multifaceted nature of these diseases, the precise underlying mechanisms remain elusive. Consequently, there is an increasing imperative to investigate the mechanisms, identify specific target sites for effective treatment, and provide for accurate diagnosis of patients with these diseases. Numerous studies have revealed significant alterations in the expression of long non-coding RNAs (lncRNAs) in psychiatric disorders and neurodegenerative diseases, suggesting their potential to increase the probability of these diseases. Moreover, these findings propose that lncRNAs could be used as highly valuable biomarkers in diagnosing and treating these diseases, thereby offering novel insights for future clinical interventions. The review presents a comprehensive summary of the origin, biological functions, and action mechanisms of lncRNAs, while exploring their implications in the pathogenesis of psychiatric disorders and neurodegenerative diseases and their potential utility as biomarkers.

Artificial intelligence significantly facilitates development in the mental health of college students: a bibliometric analysis

Objective

College students are currently grappling with severe mental health challenges, and research on artificial intelligence (AI) related to college students mental health, as a crucial catalyst for promoting psychological well-being, is rapidly advancing. Employing bibliometric methods, this study aim to analyze and discuss the research on AI in college student mental health.

Methods

Publications pertaining to AI and college student mental health were retrieved from the Web of Science core database. The distribution of publications were analyzed to gage the predominant productivity. Data on countries, authors, journal, and keywords were analyzed using VOSViewer, exploring collaboration patterns, disciplinary composition, research hotspots and trends.

Results

Spanning 2003 to 2023, the study encompassed 1722 publications, revealing notable insights: (1) a gradual rise in annual publications, reaching its zenith in 2022; (2) Journal of Affective Disorders and Psychiatry Research emerged were the most productive and influential sources in this field, with significant contributions from China, the United States, and their affiliated higher education institutions; (3) the primary mental health issues were depression and anxiety, with machine learning and AI having the widest range of applications; (4) an imperative for enhanced international and interdisciplinary collaboration; (5) research hotspots exploring factors influencing college student mental health and AI applications.

Conclusion

This study provides a succinct yet comprehensive overview of this field, facilitating a nuanced understanding of prospective applications of AI in college student mental health. Professionals can leverage this research to discern the advantages, risks, and potential impacts of AI in this critical field.

Neuromodulation and hippocampal neurogenesis in depression: A scoping review

The 'neurogenesis hypothesis of depression' emphasizes the importance of upregulated hippocampal neurogenesis for the efficacy of antidepressant treatment. Neuromodulation is a promising therapeutic method that stimulates neural circuitries to treat neuropsychiatric illnesses. We conducted a scoping review on the neurogenic and antidepressant outcomes of neuromodulation in animal models of depression. PubMed, Web of Science, and PsycInfo were comprehensively searched for full-text English articles from inception to October 5, 2021. Data screening and extraction were conducted independently by two researchers. Seventeen eligible studies were included in this review. The majority of studies used non-invasive neuromodulation (n = 14) and assessed neurogenesis using neural proliferation (n = 16) and differentiation markers (n = 9). Limited reports (n = 2) used neurogenic inhibitors to evaluate the role of neurogenesis on the depressive-like behavioral outcomes. Overall, neuromodulation substantially effectuated both hippocampal cell proliferation and antidepressant-like behavior in animal models of depression, with some providing evidence for enhanced neuronal differentiation and maturation. The proposed neurogenic-related mechanisms mediating the neuromodulation efficacies included neurotrophic processes, anti-apoptotic pathways, and normalization of HPA axis functions. Further research is warranted to explore the role of neuromodulation-induced neurogenic effects on treatment efficacies and to elucidate the underlying molecular mechanisms.

Autonomic Neural Circuit and Intervention for Comorbidity Anxiety and Cardiovascular Disease

Anxiety disorder is a prevalent psychiatric disease and imposes a significant influence on cardiovascular disease (CVD). Numerous evidence support that anxiety contributes to the onset and progression of various CVDs through different physiological and behavioral mechanisms. However, the exact role of nuclei and the association between the neural circuit and anxiety disorder in CVD remains unknown. Several anxiety-related nuclei, including that of the amygdala, hippocampus, bed nucleus of stria terminalis, and medial prefrontal cortex, along with the relevant neural circuit are crucial in CVD. A strong connection between these nuclei and the autonomic nervous system has been proven. Therefore, anxiety may influence CVD through these autonomic neural circuits consisting of anxiety-related nuclei and the autonomic nervous system. Neuromodulation, which can offer targeted intervention on these nuclei, may promote the development of treatment for comorbidities of CVD and anxiety disorders. The present review focuses on the association between anxiety-relevant nuclei and CVD, as well as discusses several non-invasive neuromodulations which may treat anxiety and CVD.

Neuroprotective Effects and Therapeutic Potential of Transcorneal Electrical Stimulation for Depression

Transcorneal electrical stimulation (TES) has emerged as a non-invasive neuromodulation approach that exerts neuroprotection via diverse mechanisms, including neurotrophic, neuroplastic, anti-inflammatory, anti-apoptotic, anti-glutamatergic, and vasodilation mechanisms. Although current studies of TES have mainly focused on its applications in ophthalmology, several lines of evidence point towards its putative use in treating depression. Apart from stimulating visual-related structures and promoting visual restoration, TES has also been shown to activate brain regions that are involved in mood alterations and can induce antidepressant-like behaviour in animals. The beneficial effects of TES in depression were further supported by its shared mechanisms with FDA-approved antidepressant treatments, including its neuroprotective properties against apoptosis and inflammation, and its ability to enhance the neurotrophic expression. This article critically reviews the current findings on the neuroprotective effects of TES and provides evidence to support our hypothesis that TES possesses antidepressant effects.

Prelimbic cortical stimulation disrupts fear memory consolidation through ventral hippocampal dopamine D2 receptors

BACKGROUND AND PURPOSE

Anxiety disorders pose one of the biggest threats to mental health worldwide, yet current therapeutics have been mostly ineffective due to issues with relapse, efficacy and toxicity of the medications. Deep brain stimulation (DBS) is a promising therapy for treatment-resistant psychiatric disorders including anxiety, but very little is known about the effects of deep brain stimulation on fear memories.

EXPERIMENTAL APPROACH

In this study, we employed a standard tone-footshock fear conditioning paradigm and modified plus maze discriminative avoidance task to probe the effects of prelimbic cortex deep brain stimulation on various stages of memory.

KEY RESULTS

We identified memory consolidation stage as a critical time point to disrupt fear memory via prelimbic cortex deep brain stimulation. The observed disruption was partially modulated by the inactivation of the ventral hippocampus and the transient changes in ventral hippocampus dopamine (D₂ ) receptors expression upon prelimbic cortex deep brain stimulation. We also observed wide-scale changes of various neurotransmitters and their metabolites in ventral hippocampus, confirming its important role in response to prelimbic cortex deep brain stimulation.

CONCLUSION AND IMPLICATIONS

These findings highlight the molecular mechanism in the ventral hippocampus in response to prelimbic cortex stimulation and may have translational value, indicating that targeting the prelimbic cortex in the memory consolidation stage via non-invasive neuromodulation techniques may be a feasible therapeutic strategy against anxiety disorders.

A Decade of Progress in Deep Brain Stimulation of the Subcallosal Cingulate for the Treatment of Depression

Major depression contributes significantly to the global disability burden. Since the first clinical study of deep brain stimulation (DBS), over 446 patients with depression have now undergone this neuromodulation therapy, and 29 animal studies have investigated the efficacy of subgenual cingulate DBS for depression. In this review, we aim to provide a comprehensive overview of the progress of DBS of the subcallosal cingulate in humans and the medial prefrontal cortex, its rodent homolog. For preclinical animal studies, we discuss the various antidepressant-like behaviors induced by medial prefrontal cortex DBS and examine the possible mechanisms including neuroplasticity-dependent/independent cellular and molecular changes. Interestingly, the response rate of subcallosal cingulate Deep brain stimulation marks a milestone in the treatment of depression. DBS achieved response and remission rates of 64–76% and 37–63%, respectively, from clinical studies monitoring patients from 6–24 months. Although some studies showed its stimulation efficacy was limited, it still holds great promise as a therapy for patients with treatment-resistant depression. Overall, further research is still needed, including more credible clinical research, preclinical mechanistic studies, precise selection of patients, and customized electrical stimulation paradigms.

Prelimbic Cortical Stimulation Improves Spatial Memory Through Distinct Patterns of Hippocampal Gene Expression in Aged Rats

Dementia poses major health challenges worldwide, yet current treatments are faced with issues of efficacy and toxicity. Deep brain stimulation (DBS) is a promising non-pharmacological treatment for dementia, but most DBS studies use young healthy animals, which may not be aetiologically relevant. In this study, we used an aged rat model in which cognitive decline occurs through a natural ageing process. We used a Morris water maze (MWM) to determine the effects of prelimbic cortex (PrL) DBS on memory in aged rats. To investigate the underlying mechanisms of the effects of DBS, we carried out microarray, quantitative PCR analysis, and mass spectrometry to detect gene expression and neurotransmitter changes in the hippocampus. We showed PrL DBS improved the performance in MWM, with related distinct patterns of gene expression involving G protein-coupled receptor pathways. We further found neurotransmitter changes in the dorsal hippocampus, which corroborated and extended the microarray findings. Our results suggest that non-neurogenesis pathways play roles in the effects of DBS. Further studies are needed to investigate the effects of DBS on memory beyond neurogenesis and to consider the highlighted pathways suggested by our data.

The Paradoxical Effect of Deep Brain Stimulation on Memory

Deep brain stimulation (DBS) is a promising treatment for many memory-related disorders including dementia, anxiety, and addiction. However, the use of DBS can be a paradoxical conundrum-dementia treatments aim to improve memory, whereas anxiety or addiction treatments aim to suppress maladaptive memory. In this review, the key hypotheses on how DBS affects memory are highlighted. We consolidate the findings and conclusions from the current research on the effects of DBS on memory in attempt to make sense of the bidirectional nature of DBS in disrupting and enhancing memory. Based on the current literature, we hypothesize that the timing of DBS plays a key role in its contradictory effects, and therefore, we propose a consolidated model of how DBS can both disrupt and enhance memory.

Eternal sunshine of the neuromodulated mind: Altering fear memories through neuromodulation

Anxiety disorders pose one of the greatest threats to mental health. Modern treatment methods exist but are hindered by relapse, toxicity, and low efficacy. The use of neuromodulation to treat anxiety disorders has shown promising results, yet its underpinning mechanisms remain poorly understood. In this review, we make the case for further development of neuromodulation techniques to alter fear memories, with particular regard to future clinical applications in treating anxiety disorders. We start by briefly summarizing the neural circuitry of fear while identifying the pros and cons of possible neuromodulation targets. We then highlight recent advances in neuromodulation techniques that have been used to alter fear memories. Next, we apply a novel network-based approach to elucidate possible mechanisms of neuromodulation which may disrupt the consolidation of fear memory. Finally, we emphasize the need for more systematic neuromodulation studies on animal models and the developing brain. Overall, we aim to provide an integrated framework for future action, identifying key research priorities that must be addressed before effective neuromodulation-based treatments can be developed for practical use.

Electrical Stimulation Normalizes c-Fos Expression in the Deep Cerebellar Nuclei of Depressive-like Rats: Implication of Antidepressant Activity

The electrical stimulation of specific brain targets has been shown to induce striking antidepressant effects. Despite that recent data have indicated that cerebellum is involved in emotional regulation, the mechanisms by which stimulation improved mood-related behaviors in the cerebellum remained largely obscure. Here, we investigated the stimulation effects of the ventromedial prefrontal cortex (vmPFC), nucleus accumbens (NAc), and lateral habenular nucleus on the c-Fos neuronal activity in various deep cerebellar and vestibular nuclei using the unpredictable chronic mild stress (CMS) animal model of depression. Our results showed that stressed animals had increased number of c-Fos cells in the cerebellar dentate and fastigial nuclei, as well as in the spinal vestibular nucleus. To examine the stimulation effects, we found that vmPFC stimulation significantly decreased the c-Fos activity within the cerebellar fastigial nucleus as compared to the CMS sham. Similarly, there was also a reduction of c-Fos expression in the magnocellular part of the medial vestibular nucleus in vmPFC- and NAc core-stimulated animals when compared to the CMS sham. Correlational analyses showed that the anxiety measure of home-cage emergence escape latency was positively correlated with the c-Fos neuronal activity of the cerebellar fastigial and magnocellular and parvicellular parts of the interposed nuclei in CMS vmPFC-stimulated animals. Interestingly, there was a strong correlation among activation in these cerebellar nuclei, indicating that the antidepressant-like behaviors were possibly mediated by the vmPFC stimulation-induced remodeling within the forebrain-cerebellar neurocircuitry.

P2X7 purinergic receptors participate in the expression and extinction processes of contextual fear conditioning memory in mice

The purinergic system consists of two large receptor families - P2X and P2Y. Both are activated by adenosine triphosphate (ATP), although presenting different functions. These receptors are present in several brain regions, including those involved in emotion and stress-related behaviors. Hence, they seem to participate in fear- and anxiety-related responses. However, few studies have investigated the purinergic system in threatening situations, as observed in contextual fear conditioning (CFC). Therefore, this study investigated the involvement of purinergic receptors in the expression and extinction of aversive memories. C57Bl/6 background mice were submitted to the CFC protocol. Wildtype (WT) mice received i.p. injection of either a nonselective P2 receptor (P2R) antagonist, P178 (10 or 30 mg/kg); a selective P2X7 receptor (P2X7R) antagonist, A438079 (10 mg/kg); a selective P2Y1 receptor (P2Y1R) antagonist, MRS2179 (10 mg/kg); or vehicle 10 min prior to or immediately after the extinction session. Additionally, P2X7R KO mice were tested in the CFC protocol. After P2R antagonist treatment, contextual fear recall increased, while acquisition of extinction was impaired. Similar results were observed with the selective P2X7R antagonist, but not with the selective P2Y1R antagonist. Interestingly, P2X7R KO mice showed increased contextual fear recall, associated with impaired acquisition of extinction, in accordance with pharmacologic P2X7R antagonism. Our results suggest that specific pharmacological or genetic blockade of P2X7R promotes anxiogenic-like effects, along with deficits in extinction learning. Thus, these receptors could present an alternative treatment of stress-related psychiatric disorders.

Choreatic Side Effects of Deep Brain Stimulation of the Anteromedial Subthalamic Nucleus for Treatment-Resistant Obsessive-Compulsive disorder

BACKGROUND

Patients with treatment-resistant obsessive-compulsive disorder (OCD) are potential candidates for deep brain stimulation (DBS). The anteromedial subthalamic nucleus (STN) is among the most commonly used targets for DBS in OCD.

CASE DESCRIPTION

We present a patient with a 30-year history of treatment-resistant OCD who underwent anteromedial STN-DBS. Despite a clear mood-enhancing effect, stimulation caused motor side effects, including bilateral hyperkinesia, dyskinesias, and sudden large amplitude choreatic movements of arms and legs when stimulating at voltages greater than approximately 1.5 V. DBS at lower amplitudes and at other contact points failed to result in a significant reduction of obsessions and compulsions without inducing motor side effects. Because of this limitation in programming options, we decided to reoperate and target the ventral capsule/ventral striatum (VC/VS), which resulted in a substantial reduction in key obsessive and compulsive symptoms without serious side effects.

CONCLUSIONS

Choreatic movements and hemiballismus have previously been linked to STN dysfunction and have been incidentally reported as side effects of DBS of the dorsolateral STN in Parkinson disease (PD). However, in PD, these side effects were usually transient, and they rarely interfered with DBS programming. In our patient, the motor side effects were persistent, and they made optimal DBS programming impossible. To our knowledge, such severe and persistent motor side effects have not been described previously for anteromedial STN-DBS.

Deep brain stimulation of the subthalamic nucleus in obsessive-compulsive disorder: Neuroanatomical and pathophysiological considerations

Obsessive-compulsive disorder (OCD) is among the most disabling chronic psychiatric disorders and has a significant negative impact on multiple domains of quality of life. For patients suffering from severe refractory OCD, deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been applied. Reviewing the literature of the last years we believe that through its central position within the cortico-basal ganglia-thalamocortical circuits, the STN has a coordinating role in decision-making and action-selection mechanisms. Dysfunctional information-processing at the level of the STN is responsible for some of the core symptoms of OCD. Research confirms an electrophysiological dysfunction in the associative and limbic (non-motor) parts of the STN. Compared to Parkinson׳s disease patients, STN neurons in OCD exhibit a lower firing rate, less frequent but longer bursts, increased burst activity in the anterior ventromedial area, an asymmetrical left-sided burst distribution, and a predominant oscillatory activity in the δ-band. Moreover, there is direct evidence for the involvement of the STN in both checking behavior and OCD symptoms, which are both related to changes in electrophysiological activity in the non-motor STN. Through a combination of mechanisms, DBS of the STN seems to interrupt the disturbed information-processing, leading to a normalization of connectivity within the cortico-basal ganglia-thalamocortical circuits and consequently to a reduction in symptoms. In conclusion, based on the STN׳s strategic position within cortico-basal ganglia-thalamocortical circuits and its involvement in action-selection mechanisms that are responsible for some of the core symptoms of OCD, the STN is a mechanism-based target for DBS in OCD.

Stimulation-Based Control of Dynamic Brain Networks

The ability to modulate brain states using targeted stimulation is increasingly being employed to treat neurological disorders and to enhance human performance. Despite the growing interest in brain stimulation as a form of neuromodulation, much remains unknown about the network-level impact of these focal perturbations. To study the system wide impact of regional stimulation, we employ a data-driven computational model of nonlinear brain dynamics to systematically explore the effects of targeted stimulation. Validating predictions from network control theory, we uncover the relationship between regional controllability and the focal versus global impact of stimulation, and we relate these findings to differences in the underlying network architecture. Finally, by mapping brain regions to cognitive systems, we observe that the default mode system imparts large global change despite being highly constrained by structural connectivity. This work forms an important step towards the development of personalized stimulation protocols for medical treatment or performance enhancement.

Brain stimulation is increasingly used in clinical settings to treat neurological disorders, but much remains unknown about how stimulation to a single brain region impacts large-scale, brain network activity. Using structural neuroimaging scans, we create computational models of brain dynamics for eight participants to explore how structure-function relationships constrain the effect of stimulation to a single region on the brain as a whole. Our results show that network control theory can be used to predict if the effects of stimulation remain focal or spread globally, and structural connectivity differentially constrains the effects of regional stimulation. Additionally, we study how stimulation of different cognitive systems spreads throughout the brain and find that stimulation of regions within the default mode network provide a mechanism to impart large change in overall brain dynamics through a densely connected structural network. By revealing how the stimulation of different brain regions and cognitive systems spreads differently through the brain, we provide a modeling framework to develop stimulation protocols to personalize medical treatments, enable performance enhancements, and facilitate cortical plasticity.

Fornix deep brain stimulation induced long-term spatial memory independent of hippocampal neurogenesis

Deep brain stimulation (DBS) is an established symptomatic treatment modality for movement disorders and constitutes an emerging therapeutic approach for the treatment of memory impairment. In line with this, fornix DBS has shown to ameliorate cognitive decline associated with dementia. Nonetheless, mechanisms mediating clinical effects in demented patients or patients with other neurological disorders are largely unknown. There is evidence that DBS is able to modulate neurophysiological activity in targeted brain regions. We therefore hypothesized that DBS might be able to influence cognitive function via activity-dependent regulation of hippocampal neurogenesis. Using stimulation parameters, which were validated to restore memory loss in a previous behavioral study, we here assessed long-term effects of fornix DBS. To do so, we injected the thymidine analog, 5-bromo-2′-deoxyuridine (BrdU), after DBS and perfused the animals 6.5 weeks later. A week prior to perfusion, memory performance was assessed in the water maze. We found that acute stimulation of the fornix improved spatial memory performance in the water maze when the probe trial was performed 1 h after the last training session. However, no evidence for stimulation-induced neurogenesis was found in fornix DBS rats when compared to sham. Our results suggest that fornix DBS improves memory functions independent of hippocampal neurogenesis, possibly through other mechanisms such as synaptic plasticity and acute neurotransmitter release.

Ventromedial prefrontal cortex stimulation enhances memory and hippocampal neurogenesis in the middle-aged rats

Memory dysfunction is a key symptom of age-related dementia. Although recent studies have suggested positive effects of electrical stimulation for memory enhancement, its potential targets remain largely unknown. In this study, we hypothesized that spatially targeted deep brain stimulation of ventromedial prefrontal cortex enhanced memory functions in a middle-aged rat model. Our results show that acute stimulation enhanced the short-, but not the long-term memory in the novel-object recognition task. Interestingly, after chronic high-frequency stimulation, both the short- and long-term memories were robustly improved in the novel-object recognition test and Morris water-maze spatial task compared to sham. Our results also demonstrated that chronic ventromedial prefrontal cortex high-frequency stimulation upregulated neurogenesis-associated genes along with enhanced hippocampal cell proliferation. Importantly, these memory behaviors were strongly correlated with the hippocampal neurogenesis. Overall, these findings suggest that chronic ventromedial prefrontal cortex high-frequency stimulation may serve as a novel effective therapeutic target for dementia-related disorders.

DOI:http://dx.doi.org/10.7554/eLife.04803.001

Memory loss in older people is a serious and widespread problem that affects up to 50% of those over the age of 85. It is a key symptom of dementia, but despite the growing impact of this disease on society, there are no treatments currently available that can effectively stop or delay the progression of the symptoms.

One therapy that may reduce memory loss is called deep brain stimulation. Electrodes are implanted into the brain and used to stimulate brain cells in particular areas of the brain to alter mental and emotional processes. Deep brain stimulation is already used to treat Parkinson's disease, depression and other conditions that affect how the brain works.

Liu et al. studied the effect of deep brain stimulation on memory in rats. The experiments show that middle-aged rats performed less well in short- and long-term memory tests than young rats. Next, Liu et al. investigated whether deep brain stimulation could improve memory in the middle-aged rats. The electrodes were positioned to stimulate a region near the front of the brain called the ‘ventromedial prefrontal cortex’; this region is important for the formation and recall of memories. Liu et al. then gave the rats a series of memory tasks that tested their recall after 90 minutes (to test their short-term memory), and after 24 hours (to test long-term memory).

The experiments reveal that a brief stimulation of brain cells in this region of the brain improved the rats' short-term memory, but not their long-term memory. However, more sustained stimulation of this region of the brain improved both the short-term and long-term memory of the rats. Furthermore, deep brain stimulation led to the formation of new brain cells in another region of the brain called the hippocampus, which is also involved in memory. The hippocampus had not been in direct contact with the electrodes so the increase in brain cells was due to its connections with the stimulated ventromedial prefrontal cortex.

Liu et al.'s findings suggest that deep brain stimulation of the ventromedial prefrontal cortex has the potential to be developed into a therapy to treat dementia and other conditions that lead to memory loss in humans.

DOI:http://dx.doi.org/10.7554/eLife.04803.002

Electrical stimulation alleviates depressive-like behaviors of rats: investigation of brain targets and potential mechanisms

Deep brain stimulation (DBS) is a promising therapy for patients with refractory depression. However, key questions remain with regard to which brain target(s) should be used for stimulation, and which mechanisms underlie the therapeutic effects. Here, we investigated the effect of DBS, with low- and high-frequency stimulation (LFS, HFS), in different brain regions (ventromedial prefrontal cortex, vmPFC; cingulate cortex, Cg; nucleus accumbens (NAc) core or shell; lateral habenula, LHb; and ventral tegmental area) on a variety of depressive-like behaviors using rat models. In the naive animal study, we found that HFS of the Cg, vmPFC, NAc core and LHb reduced anxiety levels and increased motivation for food. In the chronic unpredictable stress model, there was a robust depressive-like behavioral phenotype. Moreover, vmPFC HFS, in a comparison of all stimulated targets, produced the most profound antidepressant effects with enhanced hedonia, reduced anxiety and decreased forced-swim immobility. In the following set of electrophysiological and histochemical experiments designed to unravel some of the underlying mechanisms, we found that vmPFC HFS evoked a specific modulation of the serotonergic neurons in the dorsal raphe nucleus (DRN), which have long been linked to mood. Finally, using a neuronal mapping approach by means of c-Fos expression, we found that vmPFC HFS modulated a brain circuit linked to the DRN and known to be involved in affect. In conclusion, HFS of the vmPFC produced the most potent antidepressant effects in naive rats and rats subjected to stress by mechanisms also including the DRN.

Current perspectives on deep brain stimulation for severe neurological and psychiatric disorders

Deep brain stimulation (DBS) has become a well-accepted therapy to treat movement disorders, including Parkinson's disease, essential tremor, and dystonia. Long-term follow-up studies have demonstrated sustained improvement in motor symptoms and quality of life. DBS offers the opportunity to selectively modulate the targeted brain regions and related networks. Moreover, stimulation can be adjusted according to individual patients' demands, and stimulation is reversible. This has led to the introduction of DBS as a treatment for further neurological and psychiatric disorders and many clinical studies investigating the efficacy of stimulating various brain regions in order to alleviate severe neurological or psychiatric disorders including epilepsy, major depression, and obsessive-compulsive disorder. In this review, we provide an overview of accepted and experimental indications for DBS therapy and the corresponding anatomical targets.

The antidepressant effects of ventromedial prefrontal cortex stimulation is associated with neural activation in the medial part of the subthalamic nucleus

The nucleus accumbens (NAc), ventromedial prefrontal cortex (vmPFC), and cingulate gyrus (Cg) are key regions in the control of mood-related behaviors. Electrical stimulation of these areas induces antidepressant-like effects in both patients and animal models. Another structure whose limbic connections are receiving more interest in the context of mood-related behaviors is the medial part of the subthalamic nucleus (STN). Here, we tested the hypothesis that the mood-related effects of NAc, vmPFC, and Cg are accompanied by changes in the neural activity of the STN. We performed high-frequency stimulation (HFS) of the NAc, vmPFC, and Cg. Animals were behaviorally tested for hedonia and forced swim immobility; and the cellular activities in the different parts of the STN were assessed by means of c-Fos immunoreactivity (c-Fos-ir). Our results showed that HFS of the NAc and vmPFC, but not Cg reduced anhedonic-like and forced swim immobility behaviors. Interestingly, there was a significant increase of c-Fos-ir in the medial STN with HFS of the vmPFC, but not the NAc and Cg as compared to the sham. Correlation analysis showed that the medial STN is associated with the antidepressant-like behaviors in vmPFC HFS animals. No behavioral correlation was found with respect to behavioral outcome and activity in the lateral STN. In conclusion, HFS of the vmPFC induced profound antidepressant-like effects with enhanced neural activity in the medial part of the STN.