Chronic vagus nerve stimulation for treatment-resistant depression decreases resting ventromedial prefrontal glucose metabolism

Molecular imaging findings for treatment resistant depression

Approximately 40% of patients with major depressive disorder (MDD) had limited response to conventional antidepressant treatments, resulting in treatment-resistant depression (TRD), a debilitating subtype that yielded a significant disease burden worldwide. Molecular imaging techniques, such as positron emission tomography (PET) and single photon emission tomography (SPECT), can measure targeted macromolecules or biological processes in vivo. These imaging tools provide a unique possibility to explore the pathophysiology and treatment mechanisms underlying TRD. This work reviewed and summarized prior PET and SPECT studies to examine the neurobiology and treatment-induced changes of TRD. A total of 51 articles were included with supplementary information from studies for MDD and healthy controls (HC). We found that there were altered regional blood flow or metabolic activity in several brain regions, such as the anterior cingulate cortex, prefrontal cortex, insula, hippocampus, amygdala, parahippocampus, and striatum. These regions have been suggested to engage in the pathophysiology or treatment resistance of depression. There was also limited data to demonstrate the changes in the markers of serotonin, dopamine, amyloid, and microglia over some regions in TRD. Moreover, several observed abnormal imaging indices were linked to treatment outcomes, supporting their specificity and clinical relevance. To address the limitations of the included studies, we proposed that future studies needed longitudinal designs, multimodal approaches, and radioligands targeting specific neural substrates for TRD to evaluate their baseline and treatment-related alterations in TRD. Adequate data sharing and reproducible data analysis can facilitate advances in this field.

Non-invasive vagus nerve stimulation boosts mood recovery after effort exertion

BACKGROUND

Mood plays an important role in our life which is illustrated by the disruptive impact of aberrant mood states in depression. Although vagus nerve stimulation (VNS) has been shown to improve symptoms of depression, the exact mechanism is still elusive, and it is an open question whether non-invasive VNS could be used to swiftly and robustly improve mood.

METHODS

Here, we investigated the effect of left- and right-sided transcutaneous auricular VNS (taVNS) v. a sham control condition on mood after the exertion of physical and cognitive effort in 82 healthy participants (randomized cross-over design) using linear mixed-effects and hierarchical Bayesian analyses of mood ratings.

RESULTS

We found that 90 min of either left-sided or right-sided taVNS improved positive mood [b = 5.11, 95% credible interval, CI (1.39-9.01), 9.6% improvement relative to the mood intercept, BF₁₀ = 7.69, p_LME = 0.017], yet only during the post-stimulation phase. Moreover, lower baseline scores of positive mood were associated with greater taVNS-induced improvements in motivation [r = -0.42, 95% CI (-0.58 to -0.21), BF₁₀ = 249].

CONCLUSIONS

We conclude that taVNS boosts mood after a prolonged period of effort exertion with concurrent stimulation and that acute motivational effects of taVNS are partly dependent on initial mood states. Collectively, our results show that taVNS may help quickly improve affect after a mood challenge, potentially by modulating interoceptive signals contributing to the reappraisal of effortful behavior. This suggests that taVNS could be a useful add-on to current behavioral therapies.

Acute vagus nerve stimulation enhances reversal learning in rats

Cognitive flexibility is a prefrontal cortex-dependent neurocognitive process that enables behavioral adaptation in response to changes in environmental contingencies. Electrical vagus nerve stimulation (VNS) enhances several forms of learning and neuroplasticity, but its effects on cognitive flexibility have not been evaluated. In the current study, a within-subjects design was used to assess the effects of VNS on performance in a novel visual discrimination reversal learning task conducted in touchscreen operant chambers. The task design enabled simultaneous assessment of acute VNS both on reversal learning and on recall of a well-learned discrimination problem. Acute VNS delivered in conjunction with stimuli presentation during reversal learning reliably enhanced learning of new reward contingencies. Enhancement was not observed, however, if VNS was delivered during the session but was not coincident with presentation of to-be-learned stimuli. In addition, whereas VNS delivered at 30 HZ enhanced performance, the same enhancement was not observed using 10 or 50 Hz. Together, these data show that acute VNS facilitates reversal learning and indicate that the timing and frequency of the VNS are critical for these enhancing effects. In separate rats, administration of the norepinephrine reuptake inhibitor atomoxetine also enhanced reversal learning in the same task, consistent with a noradrenergic mechanism through which VNS enhances cognitive flexibility.

A Review of Parameter Settings for Invasive and Non-invasive Vagus Nerve Stimulation (VNS) Applied in Neurological and Psychiatric Disorders

Vagus nerve stimulation (VNS) is an established form of neuromodulation with a long history of promising applications. Earliest reports of VNS in the literature date to the late 1800’s in experiments conducted by Dr. James Corning. Over the past century, both invasive and non-invasive VNS have demonstrated promise in treating a variety of disorders, including epilepsy, depression, and post-stroke motor rehabilitation. As VNS continues to rapidly grow in popularity and application, the field generally lacks a consensus on optimum stimulation parameters. Stimulation parameters have a significant impact on the efficacy of neuromodulation, and here we will describe the longitudinal evolution of VNS parameters in the following categorical progression: (1) animal models, (2) epilepsy, (3) treatment resistant depression, (4) neuroplasticity and rehabilitation, and (5) transcutaneous auricular VNS (taVNS). We additionally offer a historical perspective of the various applications and summarize the range and most commonly used parameters in over 130 implanted and non-invasive VNS studies over five applications.

Transcutaneous Auricular Vagus Nerve Stimulation Combined With Slow Breathing: Speculations on Potential Applications and Technical Considerations

OBJECTIVES

Transcutaneous auricular vagus nerve stimulation (taVNS) is a relatively novel noninvasive neurostimulation method that is believed to mimic the effects of invasive cervical VNS. It has recently been suggested that the effectiveness of taVNS can be enhanced by combining it with controlled slow breathing. Slow breathing modulates the activity of the vagus nerve and is used in behavioral medicine to decrease psychophysiological arousal. Based on studies that examine the effects of taVNS and slow breathing separately, this article speculates on some of the conditions in which this combination treatment may prove effective. Furthermore, based on findings from studies on the optimization of taVNS and slow breathing, this article provides guidance on how to combine taVNS with slow breathing.

MATERIALS AND METHODS

A nonsystematic review.

RESULTS

Both taVNS and slow breathing are considered promising add-on therapeutic approaches for anxiety and depressive disorders, chronic pain, cardiovascular diseases, and insomnia. Therefore, taVNS combined with slow breathing may produce additive or even synergistic beneficial effects in these conditions. Studies on respiratory-gated taVNS during spontaneous breathing suggest that taVNS should be delivered during expiration. Therefore, this article proposes to use taVNS as a breathing pacer to indicate when and for how long to exhale during slow breathing exercises.

CONCLUSIONS

Combining taVNS with slow breathing seems to be a promising hybrid neurostimulation and behavioral intervention.

Neuroscience: Boosting the brain

A therapeutic effect of vagus nerve stimulation has been reported for a wide range of neurological, medical and psychiatric conditions. New research provides evidence that this effect results from extensive increase of physiological arousal and brain activation.

Variability of white matter anatomy in the subcallosal cingulate area

The subcallosal cingulate (SCC) area is a putative hub in the brain network underlying depression. Deep brain stimulation (DBS) targeting a particular subregion of SCC, identified as the intersection of forceps minor (FM), uncinate fasciculus (UCF), cingulum and fronto-striatal fiber bundles, may be critical to a therapeutic response in patients with severe, treatment-resistant forms of major depressive disorder (MDD). The pattern and variability of the white matter anatomy and organization within SCC has not been extensively characterized across individuals. The goal of this study is to investigate the variability of white matter bundles within the SCC that structurally connect this region with critical nodes in the depression network. Structural and diffusion data from 100 healthy subjects from the Human Connectome Project database were analyzed. Anatomically defined SCC regions were used as seeds to perform probabilistic tractography and to estimate the connectivity from the SCC to subject-specific target areas believed to be involved in the pathology of MDD including ventral striatum (VS), UCF, anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC). Four distinct areas of connectivity were identified within SCC across subjects: (a) postero-lateral SCC connectivity to medial temporal regions via UCF, (b) postero-medial connectivity to VS, (c) superior-medial connectivity to ACC via cingulum bundle, and (d) antero-lateral connectivity to mPFC regions via forceps minor. Assuming white matter connectivity is critical to therapeutic response, the improved anatomic understanding of SCC as well as an appreciation of the intersubject variability are critical to developing optimized therapeutic targeting for SCC DBS.

Over-activation of primate subgenual cingulate cortex enhances the cardiovascular, behavioral and neural responses to threat

Stress-related disorders such as depression and anxiety are characterized by enhanced negative emotion and physiological dysfunction. Whilst elevated activity within area 25 of the subgenual anterior cingulate cortex (sgACC/25) has been implicated in these illnesses, it is unknown whether this over-activity is causal. By combining targeted intracerebral microinfusions with cardiovascular and behavioral monitoring in marmosets, we show that over-activation of sgACC/25 reduces vagal tone and heart rate variability, alters cortisol dynamics during stress and heightens reactivity to proximal and distal threat. ¹⁸F-FDG PET imaging shows these changes are accompanied by altered activity within a network of brain regions including the amygdala, hypothalamus and dorsolateral prefrontal cortex. Ketamine, shown to have rapid antidepressant effects, fails to reverse elevated arousal to distal threat contrary to the beneficial effects we have previously demonstrated on over-activation induced reward blunting, illustrating the symptom-specificity of its actions.

Alexander et al. causally implicate over-activity in primate subgenual cingulate in affective and cardiovascular dysfunction relevant to anxiety and depression. Over-activation led to elevated activity in a stress-related network whilst decreasing activity in higher-order prefrontal cognitive regions.

Vagus nerve stimulation and Neurotrophins: a biological psychiatric perspective

Since 2004, vagus nerve stimulation (VNS) has been used in treatment-resistant or treatment-intolerant depressive episodes. Today, VNS is suggested as possible therapy for a larger spectrum of psychiatric disorders, including schizophrenia, obsessive compulsive disorders, and panic disorders. Despite a large body of literature supports the application of VNS in patients' treatment, the exact mechanism of action of VNS remains not fully understood. In the present study, the major knowledges on the brain areas and neuronal pathways regulating neuroimmune and autonomic response subserving VNS effects are reviewed. Furthermore, the involvement of the neurotrophins (NTs) Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) in vagus nerve (VN) physiology and stimulation is revised. The data on brain NGF/BDNF synthesis and in turn on the activity-dependent plasticity, connectivity rearrangement and neurogenesis, are presented and discussed as potential biomarkers for optimizing stimulatory parameters for VNS. A vagus nerve-neurotrophin interaction model in the brain is finally proposed as a working hypothesis for future studies addressed to understand pathophysiology of psychiatric disturbance.

A preliminary study of resting brain metabolism in treatment-resistant depression before and after treatment with olanzapine-fluoxetine combination

Treatment-resistant depression (TRD) occurs in many patients and causes high morbidity and mortality. Because TRD subjects are particularly difficult to study especially longitudinally, biological data remain very limited. In a preliminary study to judge feasibility and power, 25 TRD patients were referred from specialty psychiatric practices. All were severely and chronically depressed and mostly had comorbid psychiatric disorders as is typical in TRD. Nine patients were able to complete all required components of the protocol that included diagnostic interview; rating scales; clinical magnetic resonance imaging; medication washout; treatment with maximally tolerated olanzapine-fluoxetine combination for 8 weeks; and pre- and post-treatment fluorodeoxyglucose positron emission tomography. This drug combination is an accepted standard of treatment for TRD. Dropouts arose from worsening depression, insomnia, and anxiety. One patient remitted; three responded. A priori regions of interest included the amygdala and subgenual cingulate cortex (sgACC; Brodmann area BA25). Responders showed decreased metabolism with treatment in the right amygdala that correlated with clinical response; no significant changes in BA25; better response to treatment the higher the baseline BA25 metabolism; and decreased right ventromedial prefrontal metabolism (VMPFC; broader than BA25) with treatment which did not correlate with depression scores. The baseline metabolism of all individuals showed heterogeneous patterns when compared to a normative metabolic database. Although preliminary given the sample size, this study highlights several issues important for future work: marked dropout rate in this study design; need for large sample size for adequate power; baseline metabolic heterogeneity of TRD requiring careful subject characterization for future studies of interventions; relationship of amygdala activity decreases with response; and the relationship between baseline sgACC and VMPFC activity with response. Successful treatment of TRD with olanzapine-fluoxetine combination shows changes in cerebral metabolism like those seen in treatment-responsive major depression.

Effect of Electrical Vagus Nerve Stimulation on Cerebral Blood Flow and Neurological Outcome in Asphyxial Cardiac Arrest Model of Rats

BACKGROUND

Vagus nerve stimulation (VNS) during post-resuscitation may increase recovery of cerebral blood flow (CBF) and reduce neurological injury.

OBJECTIVE

This study was designed to investigate the effect of electrical VNS on neurological outcomes following cardiac arrest (CA).

METHODS

Male Sprague-Dawley rats (n = 48) were subjected to the asphyxial CA model and blindly allocated to the VN isolation (CA + VN isolation) or VNS group (CA + VNS group). Cardiopulmonary resuscitation was initiated 450 s after pulseless electrical arrest, and the left cervical vagus nerve was electrically stimulated (0.05 mA, 1 Hz) for 3 h in the CA + VNS group. The neurological deficit score (NDS) and overall performance category (OPC) were assessed at 24 h after resuscitation, and histological injury of the hippocampus was evaluated. Independent experiments were performed to evaluate the effect of VNS on global cortical CBF after resuscitation using laser speckle Doppler imaging through a thinned skull window from pre-arrest to 6 h after resuscitation.

RESULTS

The baseline characteristics were not significantly different between the two groups. The NDS was significantly higher, and the OPC was substantially lower in the CA + VNS group (p = 0.022 and p = 0.049, respectively) supported by decrease in histological injury of the hippocampal CA1 region. CBF in the early period of post-return of spontaneous circulation (ROSC) was significantly higher in the CA + VNS group (p < 0.05 at post-ROSC 2 h and 4 h), and 4-hydroxynonenal was significantly lower in the CA + VNS group (p = 0.026).

CONCLUSIONS

VNS improved cerebral perfusion and neurological outcomes at 24 h after ROSC in an asphyxial CA model of rats.

Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity

Contemplative practices, such as meditation and yoga, are increasingly popular among the general public and as topics of research. Beneficial effects associated with these practices have been found on physical health, mental health and cognitive performance. However, studies and theories that clarify the underlying mechanisms are lacking or scarce. This theoretical review aims to address and compensate this scarcity. We will show that various contemplative activities have in common that breathing is regulated or attentively guided. This respiratory discipline in turn could parsimoniously explain the physical and mental benefits of contemplative activities through changes in autonomic balance. We propose a neurophysiological model that explains how these specific respiration styles could operate, by phasically and tonically stimulating the vagal nerve: respiratory vagal nerve stimulation (rVNS). The vagal nerve, as a proponent of the parasympathetic nervous system (PNS), is the prime candidate in explaining the effects of contemplative practices on health, mental health and cognition. We will discuss implications and limitations of our model.

The Mechanism of Action of Vagus Nerve Stimulation in Treatment-Resistant Depression: Current Conceptualizations

Stimulation of the left cervical vagus nerve, or vagus nerve stimulation (VNS), brings about an antidepressant response in a subset of treatment-resistant depression (TRD) patients. How this occurs is poorly understood; however, knowledge of the neuroanatomic vagal pathways, in conjunction with functional brain imaging studies, suggests several brain regions associated with mood regulation are critical: brainstem nuclei (locus coeruleus, dorsal raphe, and ventral tegmental area), thalamus, and insular and prefrontal cortex. Furthermore, animal studies suggest that VNS enhances neuroplasticity and changes in neuronal firing patterns. Continued study to better understand the mechanism of action of VNS in TRD is warranted.

Frequency-dependent functional connectivity of the nucleus accumbens during continuous transcutaneous vagus nerve stimulation in major depressive disorder

Transcutaneous vagus nerve stimulation (tVNS) may be a promising treatment for major depressive disorder (MDD). In this exploratory study, fMRI scans were acquired during continuous real or sham tVNS from 41 MDD patients. Then, all patients received real or sham tVNS treatment for four weeks. We investigated the functional connectivity (FC) of the nucleus accumbens (NAc) at different frequency bands during real and sham tVNS and explored their associations with depressive symptom changes after one month of treatment. The results revealed: 1) significant positive FCs between the NAc and surrounding areas including the putamen, caudate, and distinct areas of the medial prefrontal cortex (MPFC) and the anterior cingulate cortex (ACC) during continuous real and sham tVNS; 2) compared with sham tVNS, real tVNS increased the FC between the left NAc and bilateral MPFC/rACC in the slow-5 band (0.008-0.027) and between the right NAc and left insula, occipital gyrus, and right lingual/fusiform gyrum in the typical low band (0.008-0.09); and 3) the FC of the NAc-MPFC/rACC during real tVNS showed a negative association with Hamilton Depression Rating Scale (HAMD) score changes in the real tVNS group after one month of treatment, but not in the sham group. Our findings demonstrate that tVNS can modulate low frequency intrinsic FC among key brain regions involved in reward and motivation processing and provide insights into the brain mechanism underlying tVNS treatment of MDD.

A Computational Model of Major Depression: the Role of Glutamate Dysfunction on Cingulo-Frontal Network Dynamics

Major depression disease (MDD) is associated with the dysfunction of multinode brain networks. However, converging evidence implicates the reciprocal interaction between midline limbic regions (typified by the ventral anterior cingulate cortex, vACC) and the dorso-lateral prefrontal cortex (dlPFC), reflecting interactions between emotions and cognition. Furthermore, growing evidence suggests a role for abnormal glutamate metabolism in the vACC, while serotonergic treatments (selective serotonin reuptake inhibitor, SSRI) effective for many patients implicate the serotonin system. Currently, no mechanistic framework describes how network dynamics, glutamate, and serotonin interact to explain MDD symptoms and treatments. Here, we built a biophysical computational model of 2 areas (vACC and dlPFC) that can switch between emotional and cognitive processing. MDD networks were simulated by slowing glutamate decay in vACC and demonstrated sustained vACC activation. This hyperactivity was not suppressed by concurrent dlPFC activation and interfered with expected dlPFC responses to cognitive signals, mimicking cognitive dysfunction seen in MDD. Simulation of clinical treatments (SSRI or deep brain stimulation) counteracted this aberrant vACC activity. Theta and beta/gamma oscillations correlated with network function, representing markers of switch-like operation in the network. The model shows how glutamate dysregulation can cause aberrant brain dynamics, respond to treatments, and be reflected in EEG rhythms as biomarkers of MDD.

Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders

The vagus nerve represents the main component of the parasympathetic nervous system, which oversees a vast array of crucial bodily functions, including control of mood, immune response, digestion, and heart rate. It establishes one of the connections between the brain and the gastrointestinal tract and sends information about the state of the inner organs to the brain via afferent fibers. In this review article, we discuss various functions of the vagus nerve which make it an attractive target in treating psychiatric and gastrointestinal disorders. There is preliminary evidence that vagus nerve stimulation is a promising add-on treatment for treatment-refractory depression, posttraumatic stress disorder, and inflammatory bowel disease. Treatments that target the vagus nerve increase the vagal tone and inhibit cytokine production. Both are important mechanism of resiliency. The stimulation of vagal afferent fibers in the gut influences monoaminergic brain systems in the brain stem that play crucial roles in major psychiatric conditions, such as mood and anxiety disorders. In line, there is preliminary evidence for gut bacteria to have beneficial effect on mood and anxiety, partly by affecting the activity of the vagus nerve. Since, the vagal tone is correlated with capacity to regulate stress responses and can be influenced by breathing, its increase through meditation and yoga likely contribute to resilience and the mitigation of mood and anxiety symptoms.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

Interoception, homeostatic emotions and sympathovagal balance

We briefly review the evidence for distinct neuroanatomical substrates that underlie interoception in humans, and we explain how they substantialize feelings from the body (in the insular cortex) that are conjoined with homeostatic motivations that guide adaptive behaviours (in the cingulate cortex). This hierarchical sensorimotor architecture coincides with the limbic cortical architecture that underlies emotions, and thus we regard interoceptive feelings and their conjoint motivations as homeostatic emotions We describe how bivalent feelings, emotions and sympathovagal balance can be organized and regulated efficiently in the bicameral forebrain as asymmetric positive/negative, approach/avoidance and parasympathetic/sympathetic components. We provide original evidence supporting this organization from studies of cardiorespiratory vagal activity in monkeys and functional imaging studies in healthy humans showing activation modulated by paced breathing and passively viewed emotional images. The neuroanatomical architecture of interoception provides deep insight into the functional organization of all emotional feelings and behaviours in humans.This article is part of the themed issue 'Interoception beyond homeostasis: affect, cognition and mental health'.

Use of deep brain stimulation for major affective disorders

The multifactorial etiology of major affective disorders, such as major depression and bipolar disorder, poses a challenge for identification of effective treatments. In a substantial number of patients, psychopharmacologic treatment does not lead to effective continuous symptom relief. The use of deep brain stimulation (DBS) for treatment-resistant patients is an investigational approach that has recently produced promising results. The recent development of safer stereotaxic neurosurgery, and the combination with functional neuroimaging to map the affected brain circuits, have led to the investigation of DBS as a potential strategy to treat major mood disorders. Several independent clinical studies have recently shown that chronic DBS treatment leads to remission of symptoms in a high number of treatment-resistant patients for major depression and bipolar disorder. In conclusion, the existing proof-of-principle that DBS can be an effective intervention for treatment-resistant depression opens new avenues for treatment. However, multicenter, randomized and blind trials need to confirm efficacy and be approved after the most recent failures. Patient selection and surgical-related improvements are key issues that remain to be addressed to help deliver more precise and customized treatment.

Adjunctive vagus nerve stimulation for treatment-resistant bipolar disorder: managing device failure or the end of battery life

The vagus nerve stimulation (VNS) device is used not only to treat refractory seizure disorders but also mood disorders; the latter indication received CE Mark approval in 2001 and Food and Drug Administration approval in 2005. Original estimates for the end of battery life (EOBL) were approximately 6-10 years. Many neuropsychiatric patients have or will soon face EOBL. A patient with severe, life-threatening, treatment-resistant bipolar disorder underwent 9 years of stable remission following 20 months of adjunctive VNS. The device ceased operation at EOBL. Because of logistical issues, re-initiation of VNS was delayed over several months. The patient relapsed with depression, mania and mixed states, and regained remission 17 months after device replacement. This case dictates prudence in managing stable patients in remission with VNS. If the device malfunctions, urgent surgical replacement is warranted with subsequent rapid titration to previous parameters as tolerated. Several months' delay may trigger relapse and prove difficult to re-establish remission.

Group differences in MEG-ICA derived resting state networks: Application to major depressive disorder

Functional magnetic resonance imaging (fMRI) studies have revealed the existence of robust, interconnected brain networks exhibiting correlated low frequency fluctuations during rest, which can be derived by examining inherent spatio-temporal patterns in functional scans independent of any a priori model. In order to explore the electrophysiological underpinnings of these networks, analogous techniques have recently been applied to magnetoencephalography (MEG) data, revealing similar networks that exhibit correlated low frequency fluctuations in the power envelope of beta band (14-30Hz) power. However, studies to date using this technique have concentrated on healthy subjects, and no method has yet been presented for group comparisons. We extended the ICA resting state MEG method to enable group comparisons, and demonstrate the technique in a sample of subjects with major depressive disorder (MDD). We found that the intrinsic resting state networks evident in fMRI appeared to be disrupted in individuals with MDD compared to healthy participants, particularly in the subgenual cingulate, although the electrophysiological correlates of this are unknown. Networks extracted from a combined group of healthy and MDD participants were examined for differences between groups. Individuals with MDD showed reduced correlations between the subgenual anterior cingulate (sgACC) and hippocampus in a network with primary nodes in the precentral and middle frontal gyri. Individuals with MDD also showed increased correlations between insulo-temporal nodes and amygdala compared to healthy controls. To further support our methods and findings, we present test/re-test reliability on independent recordings acquired within the same session. Our results demonstrate that group analyses are possible with the resting state MEG-independent component analysis (ICA) technique, highlighting a new pathway for analysis and discovery. This study also provides the first evidence of altered sgACC connectivity with a motor network. This finding, reliable across multiple sessions, suggests that the sgACC may partially mediate the psychomotor symptoms of MDD via synchronized changes in beta-band power, and expands the idea of the sgACC as a hub region mediating cognitive and emotional symptomatic domains in MDD. Findings of increased connectivity between the amygdala and cortical nodes further support the role of amygdalar networks in mediated depressive symptomatology.

CLINICAL TRIALS IDENTIFIER

NCT00024635 (ZIA-MH002927-04).

Interoceptive dysfunction: toward an integrated framework for understanding somatic and affective disturbance in depression

Depression is characterized by disturbed sleep and eating, a variety of other nonspecific somatic symptoms, and significant somatic comorbidities. Why there is such close association between cognitive and somatic dysfunction in depression is nonetheless poorly understood. An explosion of research in the area of interoception-the perception and interpretation of bodily signals-over the last decade nonetheless holds promise for illuminating what have until now been obscure links between the social, cognitive-affective, and somatic features of depression. This article reviews rapidly accumulating evidence that both somatic signaling and interoception are frequently altered in depression. This includes comparative studies showing vagus-mediated effects on depression-like behaviors in rodent models as well as studies in humans indicating both dysfunction in the neural substrates for interoception (e.g., vagus, insula, anterior cingulate cortex) and reduced sensitivity to bodily stimuli in depression. An integrative framework for organizing and interpreting this evidence is put forward which incorporates (a) multiple potential pathways to interoceptive dysfunction; (b) interaction with individual, gender, and cultural differences in interoception; and (c) a developmental psychobiological systems perspective, emphasizing likely differential susceptibility to somatic and interoceptive dysfunction across the lifespan. Combined with current theory and evidence, it is suggested that core symptoms of depression (e.g., anhedonia, social deficits) may be products of disturbed interoceptive-exteroceptive integration. More research is nonetheless needed to fully elucidate the relationship between mind, body, and social context in depression.

Pretreatment brain states identify likely nonresponse to standard treatments for depression

BACKGROUND

Treatment approaches for major depressive disorder (MDD) result in approximately one third of patients achieving remission after a first treatment. Added treatment generally improves remission rates, but approximately one third of all patients fail to respond after several treatments (sequential monotherapies or combined treatment). A pretreatment biomarker could help identify these patients. Overactivity of the subcallosal cingulate has been associated with failure of response to treatment in MDD, and it is a potential candidate for such a biomarker.

METHODS

Investigators enrolled 82 patients with MDD currently not receiving treatment in a two-phase treatment study. Patients underwent a fluorodeoxyglucose positron emission tomography scan. After scanning, patients were randomly assigned to 12 weeks of treatment with either escitalopram or cognitive-behavioral therapy (CBT). Patients not achieving remission after 12 weeks of initial treatment were treated with an additional 12 weeks of escitalopram plus CBT. Subcallosal cingulate metabolism was compared between patients who failed to achieve a response and patients who achieved remission as a result of either phase one or phase two treatment. This analysis was followed by a whole-brain analysis making the same comparison.

RESULTS

After two phases of treatment (24 weeks), 36 patients were identified as remitters, 6 patients were responders, and 9 patients were nonresponders. Subcallosal cingulate metabolism was significantly higher in nonresponders than remitters. In the follow-up whole-brain analysis, increased superior temporal sulcus activity was also associated with nonresponse to two treatments.

CONCLUSIONS

Patients with MDD who fail to achieve remission as a result of CBT or escitalopram, either alone or in combination, have a distinct brain metabolic pattern compared with patients who achieve remission as a result of CBT, escitalopram, or their combination.

Therapeutic modalities for treatment resistant depression: focus on vagal nerve stimulation and ketamine

Treatment resistant depression (TRD) is a global health concern affecting a large proportion of depressed patients who then require novel therapeutic options. One such treatment option that has received some attention in the past several years is vagal nerve stimulation (VNS). The present review briefly describes the relevance of this treatment in the light of other existing pharmacological and non-pharmacological options. It then summarizes clinical findings with respect to the efficacy of VNS. The anatomical rationale for its efficacy and other potential mechanisms of its antidepressant effects as compared to those employed by classical antidepressant drugs are discussed. VNS has been approved in some countries and has been used for patients with TRD for quite some time. A newer, fast-acting, non-invasive pharmacological option called ketamine is currently in the limelight with reference to TRD. This drug is currently in the investigational phase but shows promise. The clinical and preclinical findings related to ketamine have also been summarized and compared with those for VNS. The role of neurotrophin factors, specifically brain derived neurotrophic factor and its receptor, in the beneficial effects of both VNS and ketamine have been highlighted. It can be concluded that both these therapeutic modalities, while effective, need further research that can reveal specific targets for intervention by novel drugs and address concerns related to side-effects, especially those seen with ketamine.

Cognitive Consequences of Aging with HIV: Implications for Neuroplasticity and Rehabilitation

Combination active antiretroviral therapy prevents HIV from replicating and ravaging the immune system, thus allowing people to age with this disease. Unfortunately, the synergistic effects of HIV and aging can predispose many to become more at-risk of developing cognitive deficits which can interfere with medical management, everyday functioning, and quality of life. The purpose of this article is to describe the role of cognitive reserve and neuroplasticity on cognitive functioning in those aging with this disease. Specifically, the role of environment and the health of these individuals can compromise cognitive functioning. Fortunately, some cognitive interventions such as prevention and management of co-morbidities, cognitive remediation therapy, and neurotropic medications may be of value in preventing and rehabilitating the cognitive consequences of aging with HIV. Novel approaches such as cognitive prescriptions, transcranial direct stimulation, and binaural beat therapy may also be considered as possible techniques for cognitive rehabilitation.

Association of cerebral metabolic activity changes with vagus nerve stimulation antidepressant response in treatment-resistant depression

BACKGROUND

Vagus nerve stimulation (VNS) has antidepressant effects in treatment resistant major depression (TRMD); these effects are poorly understood. This trial examines associations of subacute (3 months) and chronic (12 months) VNS with cerebral metabolism in TRMD.

OBJECTIVE

(17)Fluorodeoxyglucose positron emission tomography was used to examine associations between 12-month antidepressant VNS response and cerebral metabolic rate for glucose (CMRGlu) changes at 3 and 12 months.

METHODS

Thirteen TRMD patients received 12 months of VNS. Depression assessments (Hamilton Depression Rating Scale [HDRS]) and PET scans were obtained at baseline (pre-VNS) and 3/12 months. CMRGlu was assessed in eight a priori selected brain regions (bilateral anterior insular [AIC], orbitofrontal [OFC], dorsolateral prefrontal [DLPFC], and anterior cingulate cortices [ACC]). Regional CMRGlu changes over time were studied in VNS responders (decreased 12 month HDRS by ≥50%) and nonresponders.

RESULTS

A significant trend (decreased 3 month CMRGlu) in the right DLPFC was observed over time in VNS responders (n = 9; P = 0.006). An exploratory whole brain analysis (P(uncorrected) = 0.005) demonstrated decreased 3 month right rostral cingulate and DLPFC CMRGlu, and increased 12 month left ventral tegmental CMRGlu in responders.

CONCLUSIONS/LIMITATIONS

VNS response may involve gradual (months in duration) brain adaptations. Early on, this process may involve decreased right-sided DLPFC/cingulate cortical activity; longer term effects (12 months) may lead to brainstem dopaminergic activation. Study limitations included: a) a small VNS nonresponders sample (N = 4), which limited conclusions about nonresponder CMRGlu changes; b) no control group; and, c) patients maintained their psychotropic medications.

Vagal blocking improves glycemic control and elevated blood pressure in obese subjects with type 2 diabetes mellitus

BACKGROUND

An active device that downregulates abdominal vagal signalling has resulted in significant weight loss in feasibility studies.

OBJECTIVE

To prospectively evaluate the effect of intermittent vagal blocking (VBLOC) on weight loss, glycemic control, and blood pressure (BP) in obese subjects with DM2.

METHODS

Twenty-eight subjects were implanted with a VBLOC device (Maestro Rechargeable System) at 5 centers in an open-label study. Effects on weight loss, HbA1c, fasting blood glucose, and BP were evaluated at 1 week to 12 months.

RESULTS

26 subjects (17 females/9 males, 51 ± 2 years, BMI 37 ± 1 kg/m(2), mean ± SEM) completed 12 months followup. One serious adverse event (pain at implant site) was easily resolved. At 1 week and 12 months, mean excess weight loss percentages (% EWL) were 9 ± 1% and 25 ± 4% (P < 0.0001), and HbA1c declined by 0.3 ± 0.1% and 1.0 ± 0.2% (P = 0.02, baseline 7.8 ± 0.2%). In DM2 subjects with elevated BP (n = 15), mean arterial pressure reduced by 7 ± 3 mmHg and 8 ± 3 mmHg (P = 0.04, baseline 100 ± 2 mmHg) at 1 week and 12 months. All subjects MAP decreased by 3 ± 2 mmHg (baseline 95 ± 2 mmHg) at 12 months.

CONCLUSIONS

VBLOC was safe in obese DM2 subjects and associated with meaningful weight loss, early and sustained improvements in HbA1c, and reductions in BP in hypertensive DM2 subjects. This trial is registered with ClinicalTrials.gov NCT00555958.

Brain imaging correlates of peripheral nerve stimulation

Direct peripheral nerve stimulation is an effective treatment for a number of disorders including epilepsy, depression, neuropathic pain, cluster headache, and urological dysfunction. The efficacy of this stimulation is ultimately due to modulation of activity in the central nervous system. However, the exact brain regions involved in each disorder and how they are modulated by peripheral nerve stimulation is not fully understood. The use of functional neuroimaging such as SPECT, PET and fMRI in patients undergoing peripheral nerve stimulation can help us to understand these mechanisms. We review the literature for functional neuroimaging performed in patients implanted with peripheral nerve stimulators for the above-mentioned disorders. These studies suggest that brain activity in response to peripheral nerve stimulation is a complex interaction between the stimulation parameters, disease type and severity, chronicity of stimulation, as well as nonspecific effects. From this information we may be able to understand which brain structures are involved in the mechanism of peripheral nerve stimulation as well as define the neural substrates underlying these disorders.

Pretreatment cerebral metabolic activity correlates with antidepressant efficacy of vagus nerve stimulation in treatment-resistant major depression: a potential marker for response?

BACKGROUND

Pretreatment brain activity in major depressive disorder correlates with response to antidepressant therapies, including pharmacotherapies and transcranial magnetic stimulation. The purpose of this trial was to examine whether pretreatment regional metabolic activity in selected regions of interest (ROIs) predicts antidepressant response following 12 months of vagus nerve stimulation (VNS) in 15 patients with treatment-resistant major depression (TRMD).

METHODS

Fluorodeoxyglucose positron emission tomography (FDG PET) was used to assess regional mean relative cerebral metabolic rate for glucose (CMRGlu) in four ROIs (anterior insular, orbitofrontal, anterior cingulate, and dorsolateral prefrontal cortices) at baseline (prior to VNS activation). Depression severity was assessed at baseline and after 12 months of VNS using the Hamilton Depression Rating Scale (HDRS), with response defined as ≥ 50% reduction in HDRS from baseline.

RESULTS

Baseline CMRGlu in the anterior insular cortex differentiated VNS responders (n=11) from nonresponders (n=4) and correlated with HDRS change (r=.64, p=.01). In a regression analysis, lower anterior insular cortex CMRGlu (p=.004) and higher orbitofrontal cortex CMRGlu (p=.047) together predicted HDRS change (R(2)=.58, p=.005). In a whole brain, voxel-wise analysis, baseline CMRGlu in the right anterior insular cortex correlated with HDRS change (r=.78, p=.001).

LIMITATIONS

Sample size was small, limiting statistical power; patients remained on their psychiatric medications; study was open-label and uncontrolled.

CONCLUSIONS

This preliminary study suggests that pretreatment regional CMRGlu may be useful in predicting response to VNS in TRMD patients.

Short-term antidepressant administration reduces negative self-referential processing in the medial prefrontal cortex in subjects at risk for depression

Depression has been associated with changes in responses within the medial prefrontal cortex (mPFC) during emotional information processing. Antidepressant drug treatment has been shown to modify neural responses in healthy volunteers early in treatment within similar circuitry. It is unclear, however, whether the same early effect occurs in depressed patients, before changes in mood. The current study therefore investigated the effects of 7-days administration of the selective serotonin-uptake inhibitor citalopram vs placebo in volunteers (n=29) at a high risk for the development of depression, using the personality phenotype of high neuroticism in a double-blind, between-groups design. On the last day of treatment, resting haemoperfusion and functional magnetic resonance imaging (MRI) data were acquired during a self-referential words categorisation task. A significant activation in a cluster of mPFC areas, including dorsal anterior cingulate and right orbitofrontal cortex was revealed, driven by decreased responses to the negative self-descriptors following citalopram compared with placebo, in the absence of any mood differences. These findings show a normalisation of neural abnormalities in- and at-risk population early in treatment, supporting the theory that antidepressants may indeed act by modifying specific neural dysfunctions correlated to negative cognitive biases.

Transcutaneous vagus nerve stimulation: retrospective assessment of cardiac safety in a pilot study

BACKGROUND

Vagus nerve stimulation has been successfully used as a treatment strategy for epilepsy and affective disorders for years. Transcutaneous vagus nerve stimulation (tVNS) is a new non-invasive method to stimulate the vagus nerve, which has been shown to modulate neuronal activity in distinct brain areas.

OBJECTIVES

Here we report effects of tVNS on cardiac function from a pilot study, which was conducted to evaluate the feasibility and safety of tVNS for the treatment of chronic tinnitus.

METHODS

Twenty-four patients with chronic tinnitus underwent treatment with tVNS over 3-10 weeks in an open single-armed pilot study. Safety criteria and practical usability of the neurostimulating device were to investigate by clinical examination and electrocardiography at baseline and at several visits during and after tVNS treatment (week 2, 4, 8, 16, and 24).

RESULTS

Two adverse cardiac events (one classified as a severe adverse event) were registered but considered very unlikely to have been caused by the tVNS device. Retrospective analyses of electrocardiographic parameters revealed a trend toward shortening of the QRS complex after tVNS.

CONCLUSION

To our knowledge this is one of the first studies investigating feasibility and safety of tVNS in a clinical sample. In those subjects with no known pre-existing cardiac pathology, preliminary data do not indicate arrhythmic effects of tVNS.

Neurostimulation therapies for treatment resistant depression: a focus on vagus nerve stimulation and deep brain stimulation

Antidepressant treatments, including pharmacotherapy and psychotherapy, do not result in remission for the majority of patients with major depressive disorder. The high prevalence of treatment resistant depression (TRD) poses a significant issue for patients as well as both societal and economic costs. Due to the limited efficacy of existing therapies in this sub-population, alternative somatic treatments are being explored. Both vagus nerve stimulation (VNS) and deep brain stimulation (DBS) are neurostimulation treatments for TRD. While VNS has Food Drug Administration approval as an adjunctive therapy for MDD, DBS is still in the experimental stages. This article will review the evidence supporting the clinical utility of these therapies.

Brain blood-flow change with acute vagus nerve stimulation in treatment-refractory major depressive disorder

BACKGROUND

Existing neuroimaging studies of vagus nerve stimulation (VNS) in treatment resistant major depression (TRMD) suggest that many brain regions (eg, prefrontal cortex, thalamus, cingulate cortex, insular cortex) associated with mood disorders undergo alterations in blood flow/metabolism.

OBJECTIVE/HYPOTHESIS

Positron emission tomography (PET oxygen-15 labeled water or PET [(15)O] H(2)O) was used to identify changes in regional cerebral blood flow (rCBF) in response to immediate VNS in 13 subjects with TRMD. We hypothesized rCBF changes along the afferent pathway of the vagus and in regions associated with depression (eg, orbitofrontal cortex, amygdala, insular cortex).

METHODS

Six 90-second PET [(15)O] H(2)O scans were performed on 13 subjects in a VNS off-on sequence. After normalization for global uptake and realignment to standard atlas space, statistical t images (P < .005) were used to evaluate rCBF change.

RESULTS

VNS induced significant rCBF decreases in the left and right lateral orbitofrontal cortex and left inferior temporal lobe. Significant increases were found in the right dorsal anterior cingulate, left posterior limb of the internal capsule/medial putamen, the right superior temporal gyrus, and the left cerebellar body. Post hoc analysis found small-to-moderate correlations between baseline acute change in rCBF and antidepressant response after 12 months of VNS.

CONCLUSIONS

Regions undergoing rCBF change in response to acute VNS are consistent with the known afferent pathway of the vagus nerve and models of brain network in depression. Larger studies assessing the correlation between acute stimulation patterns and antidepressant outcomes with VNS are needed.

Chronic vagus nerve stimulation for treatment-resistant depression increases regional cerebral blood flow in the dorsolateral prefrontal cortex

The purpose of the present study was to assess the effects of vagus nerve stimulation (VNS) therapy on regional cerebral blood flow (rCBF) in depressed patients. Regional cerebral blood flow (rCBF) was assessed by [(99m)Tc]-HMPAO-single photon emission computed tomography (SPECT) before and after 10weeks of VNS in patients participating in an open, uncontrolled European multi-center study investigating efficacy and safety of VNS. Patients suffered from major depression, with a baseline score of≥20 on the 24-item Hamilton Depression Rating Scale (HDRS) and had been unsuccessfully treated with at least two adequately prescribed antidepressant drugs. Data of 15 patients could be analyzed using SPM 2. After 10weeks of VNS (20Hz, 500μs pulse width, stimulation during 30s every 5min at the maximal comfortable level) rCBF was increased in the left dorsolateral/ventrolateral prefrontal cortex (Brodmann areas 46 and 47) and decreased in the right posterior cingulate area, the lingual gyrus and the left insula. Our findings are in line with earlier results which showed that VNS increases rCBF in the left dorsolateral prefrontal cortex. The modulation of the activity in this region could be associated with the antidepressant efficacy of VNS.

Abnormal regional spontaneous neural activity in treatment-refractory depression revealed by resting-state fMRI

Treatment-refractory depression (TRD) represents a large proportion of the depressive population, yet has seldom been investigated using advanced imaging techniques. To characterize brain dysfunction in TRD, we performed resting-state functional MRI (rs-fMRI) on 22 TRD patients, along with 26 matched healthy subjects and 22 patients who were depressed but not treatment-refractory (NDD) as comparison groups. Results were analyzed using a data-driven approach known as Regional Homogeneity (ReHo) analysis which measures the synchronization of spontaneous fMRI signal oscillations within spatially neighboring voxels. Relative to healthy controls, both depressed groups showed high ReHo primarily within temporo-limbic structures, and more widespread low ReHo in frontal, parietal, posterior fusiform cortices, and caudate. TRD patients showed more cerebral regions with altered ReHo than did NDD. Moderate but significant correlations between the altered regional ReHo and measures of clinical severity were observed in some identified clusters. These findings shed light on the pathophysiological mechanisms underlying TRD and demonstrate the feasibility of using ReHo as a research and clinical tool to monitor persistent cerebral dysfunction in depression, although further work is necessary to compare different measures of brain function to elucidate the neural substrates of these ReHo abnormalities.

Neurostimulatory and ablative treatment options in major depressive disorder: a systematic review

INTRODUCTION

Major depressive disorder is one of the most disabling and common diagnoses amongst psychiatric disorders, with a current worldwide prevalence of 5-10% of the general population and up to 20-25% for the lifetime period.

HISTORICAL PERSPECTIVE

Nowadays, conventional treatment includes psychotherapy and pharmacotherapy; however, more than 60% of the treated patients respond unsatisfactorily, and almost one fifth becomes refractory to these therapies at long-term follow-up.

NONPHARMACOLOGICAL TECHNIQUES

Growing social incapacity and economic burdens make the medical community strive for better therapies, with fewer complications. Various nonpharmacological techniques like electroconvulsive therapy, vagus nerve stimulation, transcranial magnetic stimulation, lesion surgery, and deep brain stimulation have been developed for this purpose.

DISCUSSION

We reviewed the literature from the beginning of the twentieth century until July 2009 and described the early clinical effects and main reported complications of these methods.

Chronic vagus nerve stimulation induces neuronal plasticity in the rat hippocampus

Vagus nerve stimulation (VNS) is used to treat pharmacotherapy-resistant epilepsy and depression. However, the mechanisms underlying the therapeutic efficacy of VNS remain unclear. We examined the effects of VNS on hippocampal neuronal plasticity and behaviour in rats. Cell proliferation in the hippocampus of rats subjected to acute (3 h) or chronic (1 month) VNS was examined by injection of bromodeoxyuridine (BrdU) and immunohistochemistry. Expression of doublecortin (DCX) and brain-derived neurotrophic factor (BDNF) was evaluated by immunofluorescence staining. The dendritic morphology of DCX+ neurons was measured by Sholl analysis. Our results show that acute VNS induced an increase in the number of BrdU+ cells in the dentate gyrus that was apparent 24 h and 3 wk after treatment. It also induced long-lasting increases in the amount of DCX immunoreactivity and in the number of DCX+ neurons. Neither the number of BrdU+ cells nor the amount of DCX immunoreactivity was increased 3 wk after the cessation of chronic VNS. Chronic VNS induced long-lasting increases in the amount of BDNF immunoreactivity and the number of BDNF+ cells as well as in the dendritic complexity of DCX+ neurons in the hippocampus. In contrast to chronic imipramine treatment, chronic VNS had no effect on the behaviour of rats in the forced swim or elevated plus-maze tests. Both chronic and acute VNS induced persistent changes in hippocampal neurons that may play a key role in the therapeutic efficacy of VNS. However, these changes were not associated with evident behavioural alterations characteristic of an antidepressant or anxiolytic action.

Targeted electrode-based modulation of neural circuits for depression

During the last 20 years of neuroscience research, we have witnessed a fundamental shift in the conceptualization of psychiatric disorders, with the dominant psychological and neurochemical theories of the past now complemented by a growing emphasis on developmental, genetic, molecular, and brain circuit models. Facilitating this evolving paradigm shift has been the growing contribution of functional neuroimaging, which provides a versatile platform to characterize brain circuit dysfunction underlying specific syndromes as well as changes associated with their successful treatment. Discussed here are converging imaging findings that established a rationale for testing a targeted neuromodulation strategy, deep brain stimulation, for treatment-resistant major depression.

Mourning and melancholia revisited: correspondences between principles of Freudian metapsychology and empirical findings in neuropsychiatry

Freud began his career as a neurologist studying the anatomy and physiology of the nervous system, but it was his later work in psychology that would secure his place in history. This paper draws attention to consistencies between physiological processes identified by modern clinical research and psychological processes described by Freud, with a special emphasis on his famous paper on depression entitled 'Mourning and melancholia'. Inspired by neuroimaging findings in depression and deep brain stimulation for treatment resistant depression, some preliminary physiological correlates are proposed for a number of key psychoanalytic processes. Specifically, activation of the subgenual cingulate is discussed in relation to repression and the default mode network is discussed in relation to the ego. If these correlates are found to be reliable, this may have implications for the manner in which psychoanalysis is viewed by the wider psychological and psychiatric communities.