Neurocognitive Predictors of Response in Treatment Resistant Depression to Subcallosal Cingulate Gyrus Deep Brain Stimulation

Multimodal imaging measures in the prediction of clinical response to deep brain stimulation for refractory depression: A machine learning approach

OBJECTIVES

This study compared machine learning models using unimodal imaging measures and combined multi-modal imaging measures for deep brain stimulation (DBS) outcome prediction in treatment resistant depression (TRD).

METHODS

Regional brain glucose metabolism (CMRGlu), cerebral blood flow (CBF), and grey matter volume (GMV) were measured at baseline using 18F-fluorodeoxy glucose (18F-FDG) positron emission tomography (PET), arterial spin labelling (ASL) magnetic resonance imaging (MRI), and T1-weighted MRI, respectively, in 19 patients with TRD receiving subcallosal cingulate (SCC)-DBS. Responders (n = 9) were defined by a 50% reduction in HAMD-17 at 6 months from the baseline. Using an atlas-based approach, values of each measure were determined for pre-selected brain regions. OneR feature selection algorithm and the naïve Bayes model was used for classification. Leave-out-one cross validation was used for classifier evaluation.

RESULTS

The performance accuracy of the CMRGlu classification model (84%) was greater than CBF (74%) or GMV (74%) models. The classification model using the three image modalities together led to a similar accuracy (84%0 compared to the CMRGlu classification model.

CONCLUSIONS

CMRGlu imaging measures may be useful for the development of multivariate prediction models for SCC-DBS studies for TRD. The future of multivariate methods for multimodal imaging may rest on the selection of complementing features and the developing better models.Clinical Trial Registration: ClinicalTrials.gov (#NCT01983904).

Effects of deep brain stimulation on cognitive functioning in treatment-resistant depression: a systematic review and meta-analysis

Deep brain stimulation (DBS) is a promising intervention for treatment-resistant depression (TRD). Effects on cognitive functioning are unclear since they have been studied in small samples. We aim to estimate the impact of DBS on cognitive functioning in TRD with a systematic review and meta-analyses. After systematically searching PubMed we included 10 studies which compared standardized neuropsychological tests before and after DBS or between active and sham DBS in TRD. Different random-effects meta-analyses were done for different cognitive (sub-)domains and for different follow-up time windows (<6 months, 6-18 months, and >18 months). We found no significant differences in cognitive functioning up to 6 months of DBS. After 6-18 months of DBS small to moderate improvements were found in verbal memory (Hedge's g = 0.22, 95% CI = [0.01-0.43], p = 0.04), visual memory (Hedge's g = 0.37, 95% CI = [0.03-0.71], p = 0.04), attention/psychomotor speed (Hedge's g = 0.26, 95% CI = [0.02-0.50], p = 0.04) and executive functioning (Hedge's g = 0.37, 95% CI = [0.15-0.59], p = 0.001). Not enough studies could be retrieved for a meta-analysis of effects after >18 months of DBS or for the comparison of active and sham DBS. Qualitatively, generally no differences in cognitive functioning between active and sham DBS were found. No cognitive decline was found in this meta-analysis up to 18 months of DBS in patients with TRD. Results even suggest small positive effects of DBS on cognitive functioning in TRD, although this should be interpreted with caution due to lack of controlled data.

Local neuroanatomical and tract-based proxies of optimal subcallosal cingulate deep brain stimulation

BACKGROUND

Deep brain stimulation of the subcallosal cingulate area (SCC-DBS) is a promising neuromodulatory therapy for treatment-resistant depression (TRD). Biomarkers of optimal target engagement are needed to guide surgical targeting and stimulation parameter selection and to reduce variance in clinical outcome.

OBJECTIVE/HYPOTHESIS

We aimed to characterize the relationship between stimulation location, white matter tract engagement, and clinical outcome in a large (n = 60) TRD cohort treated with SCC-DBS. A smaller cohort (n = 22) of SCC-DBS patients with differing primary indications (bipolar disorder/anorexia nervosa) was utilized as an out-of-sample validation cohort.

METHODS

Volumes of tissue activated (VTAs) were constructed in standard space using high-resolution structural MRI and individual stimulation parameters. VTA-based probabilistic stimulation maps (PSMs) were generated to elucidate voxelwise spatial patterns of efficacious stimulation. A whole-brain tractogram derived from Human Connectome Project diffusion-weighted MRI data was seeded with VTA pairs, and white matter streamlines whose overlap with VTAs related to outcome ('discriminative' streamlines; Puncorrected < 0.05) were identified using t-tests. Linear modelling was used to interrogate the potential clinical relevance of VTA overlap with specific structures.

RESULTS

PSMs varied by hemisphere: high-value left-sided voxels were located more anterosuperiorly and squarely in the lateral white matter, while the equivalent right-sided voxels fell more posteroinferiorly and involved a greater proportion of grey matter. Positive discriminative streamlines localized to the bilateral (but primarily left) cingulum bundle, forceps minor/rostrum of corpus callosum, and bilateral uncinate fasciculus. Conversely, negative discriminative streamlines mostly belonged to the right cingulum bundle and bilateral uncinate fasciculus. The best performing linear model, which utilized information about VTA volume overlap with each of the positive discriminative streamline bundles as well as the negative discriminative elements of the right cingulum bundle, explained significant variance in clinical improvement in the primary TRD cohort (R = 0.46, P < 0.001) and survived repeated 10-fold cross-validation (R = 0.50, P = 0.040). This model was also able to predict outcome in the out-of-sample validation cohort (R = 0.43, P = 0.047).

CONCLUSION(S)

These findings reinforce prior indications of the importance of white matter engagement to SCC-DBS treatment success while providing new insights that could inform surgical targeting and stimulation parameter selection decisions.

Deep brain stimulation for Parkinson’s Disease: A Review and Future Outlook

Parkinson's Disease (PD) is a neurodegenerative disorder that manifests as an impairment of motor and non-motor abilities due to a loss of dopamine input to deep brain structures. While there is presently no cure for PD, a variety of pharmacological and surgical therapeutic interventions have been developed to manage PD symptoms. This review explores the past, present and future outlooks of PD treatment, with particular attention paid to deep brain stimulation (DBS), the surgical procedure to deliver DBS, and its limitations. Finally, our group's efforts with respect to brain mapping for DBS targeting will be discussed.

Biomarkers for Deep Brain Stimulation in Animal Models of Depression

OBJECTIVES

Despite recent advances in depression treatment, many patients still do not respond to serial conventional therapies and are considered "treatment resistant." Deep brain stimulation (DBS) has therapeutic potential in this context. This comprehensive review of recent studies of DBS for depression in animal models identifies potential biomarkers for improving therapeutic efficacy and predictability of conventional DBS to aid future development of closed-loop control of DBS systems.

MATERIALS AND METHODS

A systematic search was performed in Pubmed, EMBASE, and Cochrane Review using relevant keywords. Overall, 56 animal studies satisfied the inclusion criteria.

RESULTS

Outcomes were divided into biochemical/physiological, electrophysiological, and behavioral categories. Promising biomarkers include biochemical assays (in particular, microdialysis and electrochemical measurements), which provide real-time results in awake animals. Electrophysiological tests, showing changes at both the target site and downstream structures, also revealed characteristic changes at several anatomic targets (such as the medial prefrontal cortex and locus coeruleus). However, the substantial range of models and DBS targets limits the ability to draw generalizable conclusions in animal behavioral models.

CONCLUSIONS

Overall, DBS is a promising therapeutic modality for treatment-resistant depression. Different outcomes have been used to assess its efficacy in animal studies. From the review, electrophysiological and biochemical markers appear to offer the greatest potential as biomarkers for depression. However, to develop closed-loop DBS for depression, additional preclinical and clinical studies with a focus on identifying reliable, safe, and effective biomarkers are warranted.

A piece of the puzzle: Does bipolarity partly explain the high prevalence of treatment resistance in depression?

In this cross-sectional study we examined whether the prevalence of treatment resistant depression (TRD) can be partly attributed to level of bipolarity. We included data of 201 patients with either episodic depression or TRD, who received treatment for their depression at either an outpatient or 2nd opinion/daytime setting, within a specialised mental healthcare department in the Netherlands. Whether level of TRD, assessed by the 'Dutch Measure for quantification of Treatment Resistance in Depression', can be partly explained by level of bipolarity, assessed by 'the Bipolarity Index', was examined using linear regression. We found no direct association between level of TRD and level of bipolarity, nor did comorbid anxiety disorders obscure an existing association. In this study we found no evidence for overlooked bipolarity contributing to the high prevalence of TRD. If replicated, we could state that additional screening on bipolarity with an instrument such as the 'Bipolarity Index' in the specialised mental health care is unnecessary.

Avoiding monetary loss: A human habenula functional MRI ultra-high field study

A number of convergent human neuroimaging and animal studies suggest that habenula neurons fire in anticipation of non-rewarding outcomes, and suppress their firing in anticipation of rewarding outcomes. This normative function of the habenula appears disrupted in depression, and may be critical to the anti-depressant effects of ketamine. However, studying habenula functionality in humans using standard 3 T MRI is inherently limited by its small size. We employed ultra-high field (7 T) fMRI to investigate habenular activity in eighteen healthy volunteers during a Monetary Incentive Delay Task, focussing on loss avoidance, monetary loss and neutral events. We assessed neural activation in the field of view (FOV) in addition to ROI-based habenula-specific activity and generalized task-dependent functional connectivity. Whole FOV results indicated substantial neural differences between monetary loss and neutral outcomes, as well as between loss avoidance and neutral outcomes. Habenula-specific analyses showed bilateral deactivation during loss avoidance, compared to other outcomes. This first investigation into the habenula's role during loss avoidance revealed that the left habenula further differentiated between loss avoidance and monetary loss. Functional connectivity between the right habenula and the ipsilateral hippocampus and subcallosal cingulate (regions implicated in memory and depression pathophysiology) was enhanced when anticipating potential losses compared to anticipating neutral outcomes. Our findings suggest that the human habenula responds most strongly to outcomes of loss avoidance when compared to neutral and monetary losses, suggesting a role for the habenula in both reward and aversive processing. This has critical relevance to understanding the pathophysiology of habenula function in mood and other neuropsychiatric disorders, as well as the mechanism of action of habenula-targeting antidepressants such as ketamine.

Structuro-functional surrogates of response to subcallosal cingulate deep brain stimulation for depression

Subcallosal cingulate deep brain stimulation (SCC-DBS) produces long-term clinical improvement in approximately half of patients with severe treatment-resistant depression (TRD). We hypothesized that both structural and functional brain attributes may be important in determining responsiveness to this therapy. In a TRD SCC-DBS cohort, we retrospectively examined baseline and longitudinal differences in MRI-derived brain volume (n = 65) and 18F-fluorodeoxyglucose-PET glucose metabolism (n = 21) between responders and non-responders. Support-vector machines (SVMs) were subsequently trained to classify patients' response status based on extracted baseline imaging features. A machine learning model incorporating pre-operative frontopolar, precentral/frontal opercular, and orbitofrontal local volume values classified binary response status (12 months) with 83% accuracy (leave-one-out cross-validation (LOOCV): 80% accuracy) and explained 32% of the variance in continuous clinical improvement. It was also predictive in an out-of-sample SCC-DBS cohort (n = 21) with differing primary indications (bipolar disorder/anorexia nervosa) (76% accuracy). Adding pre-operative glucose metabolism information from rostral anterior cingulate cortex and temporal pole improved model performance, enabling it to predict response status in the TRD cohort with 86% accuracy (LOOCV: 81% accuracy) and explain 67% of clinical variance. Response-related patterns of metabolic and structural post-DBS change were also observed, especially in anterior cingulate cortex and neighbouring white matter. Areas where responders differed from non-responders - both at baseline and longitudinally - largely overlapped with depression-implicated white matter tracts, namely uncinate fasciculus, cingulum bundle, and forceps minor/rostrum of corpus callosum. The extent of patient-specific engagement of these same tracts (according to electrode location and stimulation parameters) also served as a predictor of TRD response status (72% accuracy; LOOCV: 70% accuracy) and augmented performance of the volume-based (88% accuracy; LOOCV: 82% accuracy) and combined volume/metabolism-based SVMs (100% accuracy; LOOCV: 94% accuracy). Taken together, these results indicate that responders and non-responders to SCC-DBS exhibit differences in brain volume and metabolism, both pre- and post-surgery. Baseline imaging features moreover predict response to treatment (particularly when combined with information about local tract engagement) and could inform future patient selection and other clinical decisions.

Deep brain stimulation in the management of paediatric neuropsychiatric conditions: Current evidence and future directions

INTRODUCTION

Neurosurgery has provided an alternative option for patients with refractory psychiatric indications. Lesion procedures were the initial techniques used, but deep brain stimulation (DBS) has the advantage of relative reversibility and adjustability. This review sets out to delineate the current evidence for DBS use in psychiatric conditions, with an emphasis on the paediatric population, highlighting pitfalls and opportunities.

METHODS

A systematic review of the literature was conducted on studies reporting the use of DBS in the management of psychiatric disorders. The PRISMA guidelines were employed to structure the review of the literature. Data was discussed focusing on the indications for DBS management of psychiatric conditions in the paediatric age group.

RESULTS

A total of seventy-three full-text papers reported the use of DBS surgery for the management of psychiatric conditions matching the inclusion criteria. The main indications were Tourette Syndrome (GTS) (15 studies), Obsessive Compulsive Disorder (OCD) (20), Treatment Resistant Depression (TRD) (27), Eating Disorders (ED) (7) and Aggressive Behaviour and self-harm (AB) (4). Out of these, only 11 studies included patients in the paediatric age group (≤18 years-old). Among the paediatric patients, the indications for surgery included GTS, AB and ED.

CONCLUSIONS

The application of deep brain stimulation for psychiatric indications has progressed at a steady pace in the adult population and at a much slower pace in the paediatric population. Future studies in children should be done in a trial setting with strict and robust criteria. A move towards personalising DBS therapy with new stimulation paradigms will provide new frontiers and possibilities in this growing field.

Resting State Functional Connectivity Biomarkers of Treatment Response in Mood Disorders: A Review

There are currently no validated treatment biomarkers in psychiatry. Resting State Functional Connectivity (RSFC) is a popular method for investigating the neural correlates of mood disorders, but the breadth of the field makes it difficult to assess progress toward treatment response biomarkers. In this review, we followed general PRISMA guidelines to evaluate the evidence base for mood disorder treatment biomarkers across diagnoses, brain network models, and treatment modalities. We hypothesized that no treatment biomarker would be validated across these domains or with independent datasets. Results are organized, interpreted, and discussed in the context of four popular analytic techniques: (1) reference region (seed-based) analysis, (2) independent component analysis, (3) graph theory analysis, and (4) other methods. Cortico-limbic connectivity is implicated across studies, but there is no single biomarker that spans analyses or that has been replicated in multiple independent datasets. We discuss RSFC limitations and future directions in biomarker development.

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.

Deep Brain Stimulation Is Effective for Treatment-Resistant Depression: A Meta-Analysis and Meta-Regression

Major depressive disorder (MDD) is a leading cause of disability and a significant cause of mortality worldwide. Approximately 30–40% of patients fail to achieve clinical remission with available pharmacological treatments, a clinical course termed treatment-resistant depression (TRD). Numerous studies have investigated deep brain stimulation (DBS) as a therapy for TRD. We performed a meta-analysis to determine efficacy and a meta-regression to compare stimulation targets. We identified and screened 1397 studies. We included 125 citations in the qualitative review and considered 26 for quantitative analysis. Only blinded studies that compared active DBS to sham stimulation (k = 12) were included in the meta-analysis. The random-effects model supported the efficacy of DBS for TRD (standardized mean difference = −0.75, <0 favors active stimulation; p = 0.0001). The meta-regression did not demonstrate a statistically significant difference between stimulation targets (p = 0.45). While enthusiasm for DBS treatment of TRD has been tempered by recent randomized trials, this meta-analysis reveals a significant effect of DBS for the treatment of TRD. Additionally, the majority of trials have demonstrated the safety and efficacy of DBS for this indication. Further trials are required to determine the optimal stimulation parameters and patient populations for which DBS would be effective. Particular attention to factors including electrode placement technique, patient selection, and long-term follow-up is essential for future trial design.

Functional Connectivity of the Anterior Cingulate Cortex in Depression and in Health

The first voxel-level resting-state functional connectivity (FC) neuroimaging analysis of depression of the anterior cingulate cortex (ACC) showed in 282 patients with major depressive disorder compared with 254 controls, some higher, and some lower FCs. However, in 125 unmedicated patients, primarily increases of FC were found: of the subcallosal anterior cingulate with the lateral orbitofrontal cortex, of the pregenual/supracallosal anterior cingulate with the medial orbitofrontal cortex, and of parts of the anterior cingulate with the inferior frontal gyrus, superior parietal lobule, and with early cortical visual areas. In the 157 medicated patients, these and other FCs were lower than in the unmedicated group. Parcellation was performed based on the FC of individual ACC voxels in healthy controls. A pregenual subdivision had high FC with medial orbitofrontal cortex areas, and a supracallosal subdivision had high FC with lateral orbitofrontal cortex and inferior frontal gyrus. The high FC in depression between the lateral orbitofrontal cortex and the subcallosal parts of the ACC provides a mechanism for more non-reward information transmission to the ACC, contributing to depression. The high FC between the medial orbitofrontal cortex and supracallosal ACC in depression may also contribute to depressive symptoms.

Neuroanatomical predictors of response to subcallosal cingulate deep brain stimulation for treatment-resistant depression

BACKGROUND

Deep brain stimulation targeting the subcallosal cingulate gyrus (SCG DBS) improves the symptoms of treatment-resistant depression in some patients, but not in others. We hypothesized that there are pre-existing structural brain differences between responders and nonresponders to SCG DBS, detectable using structural MRI.

METHODS

We studied preoperative, T1-weighted MRI scans of 27 patients treated with SCG DBS from 2003 to 2011. Responders (n = 15) were patients with a >50% improvement in Hamilton Rating Scale for Depression score following 12 months of SCG DBS. Preoperative subcallosal cingulate gyrus grey matter volume was obtained using manual segmentation by a trained observer blinded to patient identity. Volumes of hippocampus, thalamus, amygdala, whole-brain cortical grey matter and white matter volume were obtained using automated techniques.

RESULTS

Preoperative subcallosal cingulate gyrus, thalamic and amygdalar volumes were significantly larger in patients who went on to respond to SCG-DBS. Hippocampal volume did not differ between groups. Cortical grey matter volume was significantly smaller in responders, and cortical grey matter:white matter ratio distinguished between responders and nonresponders with high sensitivity and specificity.

LIMITATIONS

Normalization by intracranial volume nullified some between-group differences in volumetric measures.

CONCLUSION

There are structural brain differences between patients with treatment-resistant depression who respond to SCG DBS and those who do not. Specifically, the structural integrity of the subcallosal cingulate gyrus target region and its connected subcortical areas, and variations in cortical volume across the entire brain, appear to be important determinants of response. Structural MRI shows promise as a biomarker in deep brain stimulation for depression, and may play a role in refining patient selection for future trials.

Effects of Estradiol Therapy on Resting-State Functional Connectivity of Transgender Women After Gender-Affirming Related Gonadectomy

An extreme incongruence between sex and gender identity leads individuals with gender dysphoria (GD) to seek cross-sex hormone therapy (CSHT), and gender-affirming surgery (GAS). Although few studies have investigated the effects of CSHT on the brain prior to GAS, no studies in the extant literature have evaluated its impact during hypogonadism in post-GAS individuals. Here, we aimed to evaluate the effects of estradiol on resting-state functional connectivity (rs-FC) of the sensorimotor cortex (SMC) and basal ganglia following surgical hypogonadism. Eighteen post-GAS (male-to-female) participants underwent functional magnetic resonance imaging (fMRI) and neuropsychiatric and hormonal assessment at two time points (t1, hormonal washout; t2, CSHT reintroduction). Based on the literature, the thalamus was selected as a seed, while the SMC and the dorsolateral striatum were targets for seed-based functional connectivity (sbFC). A second sbFC investigation consisted of a whole-brain voxel exploratory analysis again using the thalamus as a seed. A final complementary data-driven approach using multivoxel pattern analysis (MVPA) was conducted to identify a potential seed for further sbFC analyses. An increase in the rs-FC between the left thalamus and the left SCM/putamen followed CSHT. MVPA identified a cluster within the subcallosal cortex (SubCalC) representing the highest variation in peak activation between time points. Setting the SubCalC as a seed, whole-brain analysis showed a decoupling between the SubCalC and the medial frontal cortex during CSHT. These results indicate that CSHT with estradiol post-GAS, modulates rs-FC in regions engaged in cognitive, emotional, and sensorimotor processes.

Longitudinal neuropsychological outcomes in treatment-resistant depression following bed nucleus of the stria terminalis-area deep brain stimulation: a case review

Studies have demonstrated the effectiveness of deep brain stimulation (DBS) as a treatment modality for psychiatric conditions. We present a case reviewing the longitudinal neuropsychological performance outcomes following bed nucleus of the stria terminalis-area (BNST) DBS in a patient with treatment-resistant depression (TRD). The cognitive safety of DBS is well documented for various targets, however cognitive outcomes of BNST-area DBS have not been extensively reported for patients with TRD. Neuropsychological assessment was conducted pre- and post-DBS. Twelve months following DBS, augmented general cognitive performance was observed with significant changes in specific domains.

Rapid effectiveness of intravenous ketamine for ultraresistant depression in a clinical setting and evidence for baseline anhedonia and bipolarity as clinical predictors of effectiveness

BACKGROUND

Intravenous ketamine has been established as an efficacious and safe treatment, with transient effect, for treatment-resistant depression. However, the effectiveness of intravenous ketamine in non-research settings and with ultraresistant depression patients remains understudied.

AIMS

This study aims to measure the response and remission rates in ultraresistant depression patients in a clinical setting by means of a retrospective, open label, database study. Secondarily, the study will attempt to support previous findings of clinical predictors of effectiveness with intravenous ketamine treatment.

METHODS

Fifty patients with ultraresistant depression were treated between May 2015-December 2016, inclusive, in two community hospitals in Edmonton using six ketamine infusions of 0.5 mg/kg over 40 min over 2-3 weeks. Data were collected retrospectively from inpatient and outpatient charts. Statistical analysis to investigate clinical predictors of effectiveness included logistic regression analysis using a dependent variable of a 50% reduction in rating scale score at any point during treatment.

RESULTS

At baseline, the average treatment resistance was severe, with a Maudsley Staging Method score of 12.1 out of 15, 90.0% were resistant to electroconvulsive therapy, and the average Beck Depression Inventory score was 34.2. The response rate was 44% and remission rate was 16%. As a single predictor, moderate or severe anhedonia at baseline predicted a 55% increased likelihood of response. As a combined predictor, this level of anhedonia at baseline with a diagnosis of bipolar depression predicted a 73% increase in likelihood of response.

CONCLUSION

In a clinical setting, intravenous ketamine showed effectiveness in a complex, severely treatment-resistant, depressed population on multiple medication profiles concurrently. This study gave support to anhedonia and bipolar depression as clinical predictors of effectiveness.

Deep brain stimulation for treatment-resistant depression: an integrative review of preclinical and clinical findings and translational implications

Although deep brain stimulation (DBS) is an established treatment choice for Parkinson's disease (PD), essential tremor and movement disorders, its effectiveness for the management of treatment-resistant depression (TRD) remains unclear. Herein, we conducted an integrative review on major neuroanatomical targets of DBS pursued for the treatment of intractable TRD. The aim of this review article is to provide a critical discussion of possible underlying mechanisms for DBS-generated antidepressant effects identified in preclinical studies and clinical trials, and to determine which brain target(s) elicited the most promising outcomes considering acute and maintenance treatment of TRD. Major electronic databases were searched to identify preclinical and clinical studies that have investigated the effects of DBS on depression-related outcomes. Overall, 92 references met inclusion criteria, and have evaluated six unique DBS targets namely the subcallosal cingulate gyrus (SCG), nucleus accumbens (NAc), ventral capsule/ventral striatum or anterior limb of internal capsule (ALIC), medial forebrain bundle (MFB), lateral habenula (LHb) and inferior thalamic peduncle for the treatment of unrelenting TRD. Electrical stimulation of these pertinent brain regions displayed differential effects on mood transition in patients with TRD. In addition, 47 unique references provided preclinical evidence for putative neurobiological mechanisms underlying antidepressant effects of DBS applied to the ventromedial prefrontal cortex, NAc, MFB, LHb and subthalamic nucleus. Preclinical studies suggest that stimulation parameters and neuroanatomical locations could influence DBS-related antidepressant effects, and also pointed that modulatory effects on monoamine neurotransmitters in target regions or interconnected brain networks following DBS could have a role in the antidepressant effects of DBS. Among several neuromodulatory targets that have been investigated, DBS in the neuroanatomical framework of the SCG, ALIC and MFB yielded more consistent antidepressant response rates in samples with TRD. Nevertheless, more well-designed randomized double-blind, controlled trials are warranted to further assess the efficacy, safety and tolerability of these more promising DBS targets for the management of TRD as therapeutic effects have been inconsistent across some controlled studies.

Deep brain stimulation of the subcallosal cingulate gyrus in patients with treatment-resistant depression: A double-blinded randomized controlled study and long-term follow-up in eight patients

BACKGROUND

Deep brain stimulation (DBS) of the subcallosal cingulate gyrus (SCG) is an experimental approach in treatment-resistant depression (TRD). Short-term results of efficacy in DBS are incongruent and studies investigating long-term effects are warranted.

METHODS

We assessed efficacy of SCG-DBS in eight patients randomized into a delayed-onset group (sham-DBS four weeks) and a non-delayed-onset group. The primary outcome measure was improvement on the Hamilton Depression Rating-Scale (HAMD-24-item-version). Response was defined as HAMD-24 reduction of at least 50% compared to baseline. Assessment was double-blind for a period of eight weeks and after 6,- 12,- 24,- and 28,- months open-label.

RESULTS

The average improvement in HAMD-24 scores after 6,- 12,- and 24-months were 34%, 25%, and 37%. After 6 months, HAMD-24 revealed a significant difference (P = .022) and 37.5% of the patients were responders. After 12 months, HAMD-24 scores dropped, but no significant difference was observed. After 24 months, a significant improvement was found (P = .041). After the four weeks lasting sham vs. DBS-ON period, there was no group difference (P = .376) in HAMD-24 and patients did not improve during sham stimulation. Patients were followed until 28 months and two up to 4 years under SCG-DBS and average response rate was 51%, whereas two patients were remitters (33,3%).

LIMITATIONS

The small sample size limited the statistical power and external validity.

CONCLUSIONS

Long-term improvement after SCG-DBS revealed a stable effect. There was no significant difference in response rates between the delayed and non-delayed-onset group. DBS for TRD remains experimental and longitudinal investigations of large samples are needed.

A Systematic Review of Cognitive Predictors of Treatment Outcome in Major Depression

Background: Research suggests that only 50% of patients with major depression respond to psychotherapy or pharmacological treatment, and relapse is common. Therefore, there is interest in elucidating factors that help predict clinical response. Cognitive impairment is a key feature of depression, which often persists beyond remission; thus, the aim of this systematic review was to determine whether baseline cognitive functioning can predict treatment outcomes in individuals with depression. Method: Studies examining cognitive predictors of treatment response in depression were identified using Pub Med and Web of Science databases. Given the heterogeneity of outcome measures, the variety of treatment protocols, and the differing ways in which data was presented and analyzed, a narrative rather than meta-analytic review technique was used. Results: 39 studies met inclusion criteria. Findings in younger adult samples were inconclusive. There was some evidence for a predictive effect of executive function and to a lesser extent, psychomotor speed, on treatment response. There was no evidence of learning or memory being associated with treatment response. In older-aged samples, the evidence was much more consistent, suggesting that poor executive function predicts poor response to SSRIs. Conclusions: Findings from the present review suggest that certain aspects of cognitive functioning, particularly executive function, may be useful in predicting treatment response in depression. This is certainly the case in elderly samples, with evidence suggesting that poor executive functioning predicts poor response to SSRIs. With further research, baseline cognitive functioning may serve as a factor which helps guide clinical decision making. Moreover, cognitive deficits may become targets for specific pharmacological or psychological treatments, with the hope of improving overall outcome.