Neuroplasticity in depressed individuals compared with healthy controls

Depressive Symptoms Moderate the Association Between Functional Level at Admission to Intensive Post-Stroke Rehabilitation and Effectiveness of the Intervention

INTRODUCTION

Previous studies showed that depression acts as an independent factor in functional recovery after stroke. In a prospective cohort of patients admitted to intensive inpatient rehabilitation after a stroke, we aimed to test depression as a moderator of the relationship between the functional level at admission and the effectiveness of rehabilitation at discharge.

METHODS

All patients admitted to within 30 days from an ischemic or hemorrhagic stroke to 4 intensive rehabilitation units were prospectively screened for eligibility to a multicenter prospective observational study. Enrolled patients underwent an evidence-based rehabilitation pathway. We used clinical data collected at admission (T0) and discharge (T1). The outcome was the effectiveness of recovery at T1 on the modified Barthel Index (proportion of achieved over potential functional improvement). Moderation analysis was performed by using the PROCESS macro for SPSS using the bootstrapping procedure.

RESULTS

Of 278 evaluated patients, 234 were eligible and consented to enrolment; 81 patients were able to answer to the Hospital Anxiety and Depression Scale (HADS) and were included in this analysis. The relationship between the functional status at admission and rehabilitation effectiveness was significant only in persons with fewer depressive symptoms; depression (HADS cut-off score: 5.9) moderated this relationship (P = .047), independent from age and neurological impairment.

CONCLUSIONS

Our results suggest that depression moderates between the functional status at admission and the functional recovery after post-stroke rehabilitation. This approach facilitates the identification of subgroups of individuals who may respond differently to stroke rehabilitation based on depression.

Neurochemical mechanisms underlying serotonergic modulation of neuroplasticity in humans

BACKGROUND

Studies in animals and humans have shown that cortical neuroplasticity can be modulated by increasing serotonin levels by administering selective serotonin reuptake inhibitors (SSRI). However, little is known about the mechanistic background, especially the contribution of intracortical inhibition and facilitation, which depend on gamma-aminobutyric acid (GABA) and glutamate.

OBJECTIVE

We aimed to explore the relevance of drivers of plasticity (glutamate- and GABA-dependent processes) for the effects of serotonin enhancement on tDCS-induced plasticity in healthy humans.

METHODS

A crossover, partially double-blinded, randomized, and sham-controlled study was conducted in 21 healthy right-handed individuals. In each of the 7 sessions, plasticity was induced via transcranial direct current stimulation (tDCS). Anodal, cathodal, and sham tDCS were applied to the left motor cortex under SSRI (20 mg/40 mg citalopram) or placebo. Short-interval cortical inhibition (SICI) and intracortical facilitation (ICF) were monitored by paired-pulse transcranial magnetic stimulation for 5-6 h after intervention.

RESULTS

Under placebo, anodal tDCS-induced LTP-like plasticity decreased SICI and increased ICF. In contrast, cathodal tDCS-elicited LTD-like plasticity induced the opposite effect. Under 20 mg and 40 mg citalopram, anodal tDCS did not affect SICI largely, while ICF was enhanced and prolonged. For cathodal tDCS, citalopram converted the increase of SICI and decrease of ICF into antagonistic effects, and this effect was dosage-dependent since it lasted longer under 40 mg when compared to 20 mg.

CONCLUSION

We speculate that the main effects of acute serotonergic enhancement on tDCS-induced plasticity, the increase and prolongation of LTP-like plasticity effects, involves mainly the glutamatergic system.

Neuroplasticity of the left dorsolateral prefrontal cortex in patients with treatment-resistant depression as indexed with paired associative stimulation: a TMS-EEG study

Major depressive disorder affects over 300 million people globally, with approximately 30% experiencing treatment-resistant depression (TRD). Given that impaired neuroplasticity underlies depression, the present study focused on neuroplasticity in the dorsolateral prefrontal cortex (DLPFC). Here, we aimed to investigate the differences in neuroplasticity between 60 individuals with TRD and 30 age- and sex-matched healthy controls (HCs). To induce neuroplasticity, participants underwent a paired associative stimulation (PAS) paradigm involving peripheral median nerve stimulation and transcranial magnetic stimulation (TMS) targeting the left DLPFC. Neuroplasticity was assessed by using measurements combining TMS with EEG before and after PAS. Both groups exhibited significant increases in the early component of TMS-evoked potentials (TEP) after PAS (P < 0.05, paired t-tests with the bootstrapping method). However, the HC group demonstrated a greater increase in TEPs than the TRD group (P = 0.045, paired t-tests). Additionally, event-related spectral perturbation analysis highlighted that the gamma power significantly increased after PAS in the HC group, whereas it was decreased in the TRD group (P < 0.05, paired t-tests with the bootstrapping method). This gamma power modulation revealed a significant group difference (P = 0.006, paired t-tests), indicating an inverse relationship for gamma power modulation. Our findings underscore the impaired neuroplasticity of the DLPFC in individuals with TRD.

Effect of Transcranial Direct Current Stimulation (tDCS) on Depression in Parkinson's Disease-A Narrative Review

INTRODUCTION

Depression is the most prevalent comorbid neuropsychiatric condition in individuals with Parkinson's disease (PD), and its underlying mechanisms are not yet fully understood. Current treatment methods are characterised by moderate effectiveness and possible side effects, prompting the search for new non-invasive and safe treatment methods.

METHODS

This narrative review explores the use of transcranial direct current stimulation (tDCS) in the treatment of depression in PD, based on neuropsychological measures. Searches were conducted in the PubMed/Medline, Research Gate, and Cochrane databases.

RESULTS

Nine relevant studies were identified, where depression scores served as either primary or secondary outcomes. Stimulation protocols displayed heterogeneity, especially concerning choice of stimulation site. Patient samples were also heterogeneous. The majority of the studies incorporated anodal stimulation targeting the left dorsolateral prefrontal cortex (DLPFC). The results revealed a reduction in depression scores among PD patients following tDCS. Potential mechanisms through which tDCS may alleviate depression in PD were discussed and recommendations for future research were made.

CONCLUSIONS

Preliminary evidence suggests that tDCS applied anodally to the left DLPFC reduces depression scores in people with PD; however, due to the heterogeneity of the studies analysed, the use of tDCS in this field should be approached with caution and warrants further validation and confirmation.

Targeting metaplasticity mechanisms to promote sustained antidepressant actions

The discovery that subanesthetic doses of (R, S)-ketamine (ketamine) and (S)-ketamine (esketamine) rapidly induce antidepressant effects and promote sustained actions following drug clearance in depressed patients who are treatment-resistant to other therapies has resulted in a paradigm shift in the conceptualization of how rapidly and effectively depression can be treated. Consequently, the mechanism(s) that next generation antidepressants may engage to improve pathophysiology and resultant symptomology are being reconceptualized. Impaired excitatory glutamatergic synapses in mood-regulating circuits are likely a substantial contributor to the pathophysiology of depression. Metaplasticity is the process of regulating future capacity for plasticity by priming neurons with a stimulation that alters later neuronal plasticity responses. Accordingly, the development of treatment modalities that specifically modulate the duration, direction, or magnitude of glutamatergic synaptic plasticity events such as long-term potentiation (LTP), defined here as metaplastogens, may be an effective approach to reverse the pathophysiology underlying depression and improve depression symptoms. We review evidence that the initiating mechanisms of pharmacologically diverse rapid-acting antidepressants (i.e., ketamine mimetics) converge on consistent downstream molecular mediators that facilitate the expression/maintenance of increased synaptic strength and resultant persisting antidepressant effects. Specifically, while the initiating mechanisms of these therapies may differ (e.g., cell type-specificity, N-methyl-D-aspartate receptor (NMDAR) subtype-selective inhibition vs activation, metabotropic glutamate receptor 2/3 antagonism, AMPA receptor potentiation, 5-HT receptor-activating psychedelics, etc.), the sustained therapeutic mechanisms of putative rapid-acting antidepressants will be mediated, in part, by metaplastic effects that converge on consistent molecular mediators to enhance excitatory neurotransmission and altered capacity for synaptic plasticity. We conclude that the convergence of these therapeutic mechanisms provides the opportunity for metaplasticity processes to be harnessed as a druggable plasticity mechanism by next-generation therapeutics. Further, targeting metaplastic mechanisms presents therapeutic advantages including decreased dosing frequency and associated diminished adverse responses by eliminating the requirement for the drug to be continuously present.

Neuroplasticity: The Continuum of Change

Neuroplasticity is a term that is increasingly permeating mainstream discourse and being used by the popular press to simplify descriptions of how the brain changes in response to stimuli such as exercise, sleep, food, drugs of abuse, and medicines, among others. However, it is a complex, multifaceted concept representing a continuum connecting molecular, cellular, and circuit-level changes and their effects on human behavior. In this Viewpoint, we examine neuroplasticity from several perspectives to construct a holistic view of this ambiguous term. By engaging experts across various scientific disciplines, we attempt to provide an easy entry point to the concept of neuroplasticity for readers of ACS Chemical Neuroscience. By highlighting how neuroplasticity changes in both health and disease, we demonstrate that the concept is applicable to both adaptive and maladaptive responses to stimuli, underscoring its significance in chemical neuroscience.

Exploratory genome-wide analyses of cortical inhibition, facilitation, and plasticity in late-life depression

Late-life depression (LLD) is a heterogenous mood disorder influenced by genetic factors. Cortical physiological processes such as cortical inhibition, facilitation, and plasticity may be markers of illness that are more strongly associated with genetic factors than the clinical phenotype. Thus, exploring the relationship between genetic factors and these physiological processes may help to characterize the biological mechanisms underlying LLD and improve diagnosis and treatment selection. Transcranial magnetic stimulation (TMS) combined with electromyography was used to measure short interval intracortical inhibition (SICI), cortical silent period (CSP), intracortical facilitation (ICF), and paired associative stimulation (PAS) in 79 participants with LLD. We used exploratory genome-wide association and gene-based analyses to assess for genetic correlations of these TMS measures. MARK4 (which encodes microtubule affinity-regulating kinase 4) and PPP1R37 (which encodes protein phosphatase 1 regulatory subunit 37) showed genome-wide significant association with SICI. EGFLAM (which encodes EGF-like fibronectin type III and laminin G domain) showed genome-wide significant association with CSP. No genes met genome-wide significant association with ICF or PAS. We observed genetic influences on cortical inhibition in older adults with LLD. Replication with larger sample sizes, exploration of clinical phenotype subgroups, and functional analysis of relevant genotypes is warranted to better characterize genetic influences on cortical physiology in LLD. This work is needed to determine whether cortical inhibition may serve as a biomarker to improve diagnostic precision and guide treatment selection in LLD.

Abnormal volumetric brain morphometry and cerebral blood flow in adolescents with depression

BACKGROUND

Prior research has demonstrated that the brains of adolescents with depression exhibit distinct structural alterations. However, preliminary studies have documented the pathophysiological changes in certain brain regions, such as the cerebellum, highlighting a need for further research to support the current understanding of this disease.

AIM

To study brain changes in depressed adolescents.

METHODS

This study enrolled 34 adolescents with depression and 34 age-, sex-, and education-level-matched healthy control (HC) individuals. Structural and functional alterations were identified when comparing the brains of these two participant groups through voxel-based morphometry and cerebral blood flow (CBF) analysis, respectively. Associations between identified brain alterations and the severity of depressive symptoms were explored through Pearson correlation analyses.

RESULTS

The cerebellum, superior frontal gyrus, cingulate gyrus, pallidum, middle frontal gyrus, angular gyrus, thalamus, precentral gyrus, inferior temporal gyrus, superior temporal gyrus, inferior frontal gyrus, and supplementary motor areas of adolescents with depression showed an increase in brain volume compared to HC individuals. These patients with depression further presented with a pronounced drop in CBF in the left pallidum (group = 98, and peak t = - 4.4324), together with increased CBF in the right percental gyrus (PerCG) (group = 90, and peak t = 4.5382). In addition, 17-item Hamilton Depression Rating Scale scores were significantly correlated with the increased volume in the opercular portion of the left inferior frontal gyrus (r = - 0.5231, P < 0.01).

CONCLUSION

The right PerCG showed structural and CBF changes, indicating that research on this part of the brain could offer insight into the pathophysiological causes of impaired cognition.

Replicability of motor cortex-excitability modulation by intermittent theta burst stimulation

OBJECTIVE

Transcranial Magnetic Stimulation (TMS) allows for cortical-excitability (CE) assessment and its modulation has been associated with neuroplasticity-like phenomena, thought to be impaired in neuropsychiatric disorders. However, the stability of these measures has been challenged, defying their potential as biomarkers. This study aimed to test the temporal stability of cortical-excitability modulation and study the impact of individual and methodological factors in determining within- and between-subject variability.

METHODS

We recruited healthy-subjects to assess motor cortex (MC) excitability modulation, collecting motor evoked potentials (MEP) from both hemispheres, before and after left-sided intermittent theta burst stimulation (iTBS), to obtain a measure of MEPs change (delta-MEPs). To assess stability across-time, the protocol was repeated after 6 weeks. Socio-demographic and psychological variables were collected to test association with delta-MEPs.

RESULTS

We found modulatory effects on left MC and not on right hemisphere following iTBS of left MC. Left delta-MEP was stable across-time when performed immediately after iTBS (ICC = 0.69), only when obtained first in left hemisphere. We discovered similar results in a replication cohort testing only left MC (ICC = 0.68). No meaningful associations were found between demographic and psychological factors and delta-MEPs.

CONCLUSIONS

Delta-MEP is stable immediately after modulation and not impacted by different individual factors, including expectation about TMS-effect.

SIGNIFICANCE

Motor cortex excitability modulation immediately after iTBS should be further explored as a potential biomarker for neuropsychiatric diseases.

Challenging the Pleiotropic Effects of Repetitive Transcranial Magnetic Stimulation in Geriatric Depression: A Multimodal Case Series Study

BACKGROUND

Although the antidepressant potential of repetitive transcranial magnetic stimulation (rTMS), the pleiotropic effects in geriatric depression (GD) are poorly investigated. We tested rTMS on depression, cognitive performance, growth/neurotrophic factors, cerebral blood flow (CBF) to transcranial Doppler sonography (TCD), and motor-evoked potentials (MEPs) to TMS in GD.

METHODS

In this case series study, six drug-resistant subjects (median age 68.0 years) underwent MEPs at baseline and after 3 weeks of 10 Hz rTMS on the left dorsolateral prefrontal cortex. The percentage change of serum nerve growth factor, vascular endothelial growth factor, brain-derived growth factor, insulin-like growth factor-1, and angiogenin was obtained. Assessments were performed at baseline, and at the end of rTMS; psychocognitive tests were also repeated after 1, 3, and 6 months.

RESULTS

Chronic cerebrovascular disease was evident in five patients. No adverse/undesirable effect was reported. An improvement in mood was observed after rTMS but not at follow-up. Electrophysiological data to TMS remained unchanged, except for an increase in the right median MEP amplitude. TCD and neurotrophic/growth factors did not change.

CONCLUSIONS

We were unable to detect a relevant impact of high-frequency rTMS on mood, cognition, cortical microcircuits, neurotrophic/growth factors, and CBF. Cerebrovascular disease and exposure to multiple pharmacological treatments might have contributed.

Psychiatric symptoms in multiple sclerosis: a biological perspective on synaptic and network dysfunction

Psychiatric symptoms frequently occur in multiple sclerosis (MS), presenting with a complex phenomenology that encompasses a large clinical spectrum from clear-cut psychiatric disorders up to isolated psychopathological manifestations. Despite their relevant impact on the overall disease burden, such clinical features are often misdiagnosed, receive suboptimal treatment and are not systematically evaluated in the quantification of disease activity. The development of psychiatric symptoms in MS underpins a complex pathogenesis involving both emotional reactions to a disabling disease and structural multifocal central nervous system damage. Here, we review MS psychopathological manifestations under a biological perspective, highlighting the pathogenic relevance of synaptic and neural network dysfunction. Evidence obtained from human and experimental disease models suggests that MS-related psychiatric phenomenology is part of a disconnection syndrome due to diffuse inflammatory and neurodegenerative brain damage.

The M1 muscarinic acetylcholine receptor regulates the surface expression of the AMPA receptor subunit GluA2 via PICK1

Muscarinic acetylcholine receptors (mAChRs) have been shown to play significant roles in the regulation of normal cognitive processes in the hippocampus, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are also involved in these processes. This study aims to explore the mAChR-mediated regulation of AMPARs GluA2 trafficking and to reveal the key proteins and the signaling cascade involved in this process. Primary hippocampal neurons, as cell models, were treated with agonist 77-LH-28-1 and antagonist VU0255035, Fsc231, and APV. C57BL/6J male mice were stereotactically injected with 77-LH-28-1 and Fsc231 to obtain hippocampal slices. The trafficking of GluA2 was detected by surface biotinylation and immunostaining. Activation of M1 mAChRs promoted endocytosis and decreased the postsynaptic localization of the AMPA receptor subunit GluA2 and that phosphorylation of GluA2 at Ser880 was increased by M1 mAChR activity. Fsc231 blocked the endocytosis and postsynaptic localization of GluA2 induced by 77-LH-28-1 without affecting the phosphorylation of Ser880. PICK1 was required for M1 mAChR-mediated GluA2 endocytosis and downstream of phosphorylation of GluA2-Ser880, and the PICK1-GluA2 interaction was essential for M1 mAChR-mediated postsynaptic expression of GluA2. Taken together, our results show a functional correlation of M1 mAChRs with GluA2 and the role of PICK1 in their interplay. The schematic diagram for the modulation of GluA2 trafficking by M1 mAChRs. Activation of M1 mAChRs induces PKC activation, and the interaction of PICK1-GluA2 determines the endocytosis and postsynaptic localization of GluA2.

Towards an understanding of psychedelic-induced neuroplasticity

Classic psychedelics, such as LSD, psilocybin, and the DMT-containing beverage ayahuasca, show some potential to treat depression, anxiety, and addiction. Importantly, clinical improvements can last for months or years after treatment. It has been theorized that these long-term improvements arise because psychedelics rapidly and lastingly stimulate neuroplasticity. The focus of this review is on answering specific questions about the effects of psychedelics on neuroplasticity. Firstly, we review the evidence that psychedelics promote neuroplasticity and examine the cellular and molecular mechanisms behind the effects of different psychedelics on different aspects of neuroplasticity, including dendritogenesis, synaptogenesis, neurogenesis, and expression of plasticity-related genes (e.g., brain-derived neurotrophic factor and immediate early genes). We then examine where in the brain psychedelics promote neuroplasticity, particularly discussing the prefrontal cortex and hippocampus. We also examine what doses are required to produce this effect (e.g., hallucinogenic doses vs. "microdoses"), and how long purported changes in neuroplasticity last. Finally, we discuss the likely consequences of psychedelics' effects on neuroplasticity for both patients and healthy people, and we identify important research questions that would further scientific understanding of psychedelics' effects on neuroplasticity and its potential clinical applications.

Glutamate receptor 4 as a fluid biomarker for the diagnosis of psychiatric disorders

Psychiatric disorders are widely underreported diseases, especially in their early stages. So far, there is no fluid biomarker to confirm the diagnosis of these disorders. Proteomics data suggest the synaptic protein glutamate receptor 4 (GluR4), part of the AMPA receptor, as a potential diagnostic biomarker of major depressive disorder (MDD). A novel sandwich ELISA was established and analytically validated to detect GluR4 in cerebrospinal fluid (CSF) samples. A total of 85 subjects diagnosed with MDD (n = 36), bipolar disorder (BD, n = 12), schizophrenia (SCZ, n = 12) and neurological controls (CON, n = 25) were analysed. The data exhibited a significant correlation (r = 0.74; CI:0.62 to 0.82; p < 0.0001) with the antibody-free multiple reaction monitoring (MRM) mass spectrometry (MS) data. CSF GluR4 levels were lower in MDD (p < 0.002) and BD (p = 0.012) than in CON. Moreover, subjects with SCZ described a trend towards lower levels than CON (p = 0.13). The novel GluR4 ELISA may favour the clinical application of this protein as a potential diagnostic biomarker of psychiatric disorders and may facilitate the understanding of the pathophysiological mechanisms behind these disorders.

Efficacy of Adjunctive D-Cycloserine to Intermittent Theta-Burst Stimulation for Major Depressive Disorder: A Randomized Clinical Trial

Importance

The antidepressant effects of transcranial magnetic stimulation protocols for major depressive disorder (MDD) are thought to depend on synaptic plasticity. The theta-burst stimulation (TBS) protocol synaptic plasticity is known to be N-methyl-D-aspartate (NMDA)-receptor dependent, yet it is unknown whether enhancing NMDA-receptor signaling improves treatment outcomes in MDD.

Objective

To test whether low doses of the NMDA-receptor partial-agonist, D-cycloserine, would enhance intermittent TBS (iTBS) treatment outcomes in MDD.

Design, Setting, and Participants

This was a single-site 4-week, double-blind, placebo-controlled, randomized clinical trial conducted from November 6, 2019, to December 24, 2020, including 50 participants with MDD. Participants were recruited via advertisements and referral. Inclusion criteria were as follows: age 18 to 65 years with a primary diagnosis of MDD, a major depressive episode with score of 18 or more on the 17-item Hamilton Depression Rating Scale, a Young Mania Rating Scale score of 8 or less, and normal blood work (including complete blood cell count, electrolytes, liver function tests, and creatinine level).

Interventions

Participants were randomly assigned 1:1 to either iTBS plus placebo or iTBS plus D-cycloserine (100 mg) for the first 2 weeks followed by iTBS without an adjunct for weeks 3 and 4.

Main Outcomes and Measures

The primary outcome was change in depressive symptoms as measured by the Montgomery-Åsberg Depression Rating Scale (MADRS) at the conclusion of treatment. Secondary outcomes included clinical response, clinical remission, and Clinical Global Impression (CGI) scores.

Results

A total of 50 participants (mean [SD] age, 40.8 [13.4] years; 31 female [62%]) were randomly assigned to treatment groups: iTBS plus placebo (mean [SD] baseline score, 30.3 [4.2]) and iTBS plus D-cycloserine (mean [SD] baseline score, 30.4 [4.5]). The iTBS plus D-cycloserine group had greater improvements in MADRS scores compared with the iTBS plus placebo group (mean difference, -6.15; 95% CI, -2.43 to -9.88; Hedges g = 0.99; 95% CI, 0.34-1.62). Rates of clinical response were higher in the iTBS plus D-cycloserine group than in the iTBS plus placebo group (73.9% vs 29.3%), as were rates of clinical remission (39.1% vs 4.2%). This was reflected in lower CGI-severity ratings and greater CGI-improvement ratings. No serious adverse events occurred.

Conclusions and Relevance

Findings from this clinical trial indicate that adjunctive D-cycloserine may be a promising strategy for enhancing transcranial magnetic stimulation treatment outcomes in MDD using iTBS requiring further investigation.

Trial Registration

ClinicalTrials.gov Identifier: NCT03937596.

Dysregulation of adult hippocampal neuroplasticity in major depression: pathogenesis and therapeutic implications

Major depressive disorder (MDD) was previously hypothesized to be a disease of monoamine deficiency in which low levels of monoamines in the synaptic cleft were believed to underlie depressive symptoms. More recently, however, there has been a paradigm shift toward a neuroplasticity hypothesis of depression in which downstream effects of antidepressants, such as increased neurogenesis, contribute to improvements in cognition and mood. This review takes a top-down approach to assess how changes in behavior and hippocampal-dependent circuits may be attributed to abnormalities at the molecular, structural, and synaptic level. We conclude with a discussion of how antidepressant treatments share a common effect in modulating neuroplasticity and consider outstanding questions and future perspectives.

Long-Term Potentiation-Like Visual Synaptic Plasticity Is Negatively Associated With Self-Reported Symptoms of Depression and Stress in Healthy Adults

Long-term potentiation (LTP) is one of the most extensively studied forms of neuroplasticity and is considered the strongest candidate mechanism for memory and learning. The use of event-related potentials and sensory stimulation paradigms has allowed for the translation from animal studies to non-invasive studies of LTP-like synaptic plasticity in humans. Accumulating evidence suggests that synaptic plasticity as measured by stimulus-specific response modulation is reduced in neuropsychiatric disorders such as major depressive disorder (MDD), bipolar disorders and schizophrenia, suggesting that impaired synaptic plasticity plays a part in the underlying pathophysiology of these disorders. This is in line with the neuroplasticity hypothesis of depression, which postulate that deficits in neuroplasticity might be a common pathway underlying depressive disorders. The current study aims to replicate and confirm earlier reports that visual stimulus-specific response modulation is a viable probe into LTP-like synaptic plasticity in a large sample of healthy adults (n = 111). Further, this study explores whether impairments in LTP-like synaptic plasticity is associated with self-reported subclinical depressive symptoms and stress in a healthy population. Consistent with prior research, the current study replicated and confirmed reports demonstrating significant modulation of visual evoked potentials (VEP) following visual high-frequency stimulation. Current results further indicate that reduced LTP-like synaptic plasticity is associated with higher levels of self-reported symptoms of depression and perceived stress. This indicate that LTP-like plasticity is sensitive to sub-clinical levels of psychological distress, and might represent a vulnerability marker for the development of depressive symptoms.

Corticomotor plasticity as a predictor of response to high frequency transcranial magnetic stimulation treatment for major depressive disorder

BACKGROUND

Many patients with treatment-resistant depression (TRD) respond to repetitive transcranial magnetic stimulation (rTMS) treatment. This study aimed to investigate whether modulation of corticomotor excitability by rTMS predicts response to rTMS treatment for TRD in 10 Hz and intermittent theta-burst stimulation (iTBS) protocols.

METHODS

Thirteen TRD patients underwent two evaluations of corticomotor plasticity-assessed as the post-rTMS (10 Hz, iTBS) percent change (%∆) in motor evoked potential (MEP) amplitude elicited by single-pulse TMS. Following corticomotor plasticity evaluations, patients subsequently underwent a standard 6-week course of 10 Hz rTMS (4 s train, 26 s inter-train interval, 3000 total pulses, 120% of motor threshold) to the left dorsolateral prefrontal cortex. Treatment efficacy was assessed by the Beck Depression Inventory II (BDI-II) and Hamilton Depression Rating Scale (HAM-D). The change in MEPs was compared between 10 Hz and iTBS conditions and related to the change in BDI-II and HAM-D scores.

RESULTS

Analyses of variance revealed that across all time-points, higher post-10 Hz MEP change was a significant predictor of greater improvement on the BDI-II (p < 0.001) and HAM-D (p = 0.022). This relationship was not observed with iTBS (p-values≥0.100). Post-hoc tests revealed the MEP change 20 min post-10 Hz was the strongest predictor of BDI-II improvement.

LIMITATIONS

Cortical excitability was measured from the motor cortex, rather than the dorsolateral prefrontal cortex, where treatment is applied. The 10 Hz and iTBS protocols were performed at different intensities consistent with common practice.

CONCLUSIONS

Modulation of corticomotor excitability by 10 Hz can predict response to rTMS treatment with 10 Hz rTMS.

Transcranial Magnetic Stimulation Indices of Cortical Excitability Enhance the Prediction of Response to Pharmacotherapy in Late-Life Depression

BACKGROUND

Older adults with late-life depression (LLD) often experience incomplete or lack of response to first-line pharmacotherapy. The treatment of LLD could be improved using objective biological measures to predict response. Transcranial magnetic stimulation (TMS) can be used to measure cortical excitability, inhibition, and plasticity, which have been implicated in LLD pathophysiology and associated with brain stimulation treatment outcomes in younger adults with depression. TMS measures have not yet been investigated as predictors of treatment outcomes in LLD or pharmacotherapy outcomes in adults of any age with depression.

METHODS

We assessed whether pretreatment single-pulse and paired-pulse TMS measures, combined with clinical and demographic measures, predict venlafaxine treatment response in 76 outpatients with LLD. We compared the predictive performance of machine learning models including or excluding TMS predictors.

RESULTS

Two single-pulse TMS measures predicted venlafaxine response: cortical excitability (neuronal membrane excitability) and the variability of cortical excitability (dynamic fluctuations in excitability levels). In cross-validation, models using a combination of these TMS predictors, clinical markers of treatment resistance, and age classified patients with 73% ± 11% balanced accuracy (average correct classification rate of responders and nonresponders; permutation testing, p < .005); these models significantly outperformed (corrected t test, p = .025) models using clinical and demographic predictors alone (60% ± 10% balanced accuracy).

CONCLUSIONS

These preliminary findings suggest that single-pulse TMS measures of cortical excitability may be useful predictors of response to pharmacotherapy in LLD. Future studies are needed to confirm these findings and determine whether combining TMS predictors with other biomarkers further improves the accuracy of predicting LLD treatment outcome.

Shaping plasticity with non-invasive brain stimulation in the treatment of psychiatric disorders: Present and future

The final chapter of this book addresses plasticity in the setting of treating psychiatric disorders. This chapter largely focuses on the treatment of depression and reviews the established antidepressant brain stimulation treatments, focusing on plasticity and maladaptive plasticity. Depression is a unique neuropsychiatric disease in that the brain goes from a healthy state into a pathologic state, and then, with appropriate treatment, can return to health often without permanent sequelae. Depression thus differs fundamentally from neurodegenerative brain diseases like Parkinson's disease or stroke. Some have theorized that depression involves a lack of flexibility or a lack of plasticity. The proven brain stimulation methods for treating depression cause plastic changes and include acute and maintenance electroconvulsive therapy (ECT), acute and maintenance transcranial magnetic stimulation (TMS), and chronically implanted cervical vagus nerve stimulation (VNS). These treatments vary widely in their speed of onset and durability. This variability in onset speed and durability raises interesting, and so far, largely unanswered questions about the underlying neurobiological mechanisms and forms of plasticity being invoked. The chapter also covers exciting recent work with vagus nerve stimulation (VNS) that is delivered paired with behaviors to cause learning and memory and plasticity changes. Taken together these current and future brain stimulation treatments for psychiatric disorders are especially promising. They are unlocking how to shape the brain in diseases to restore balance and health, with an increasing understanding of how to effectively and precisely induce therapeutic neuroplastic changes in the brain.

Cortical Inhibition and Plasticity in Major Depressive Disorder

BACKGROUND

Major depressive disorder (MDD) is a severe psychiatric disorder that is associated with various cognitive impairments, including learning and memory deficits. As synaptic plasticity is considered an important mechanism underlying learning and memory, deficits in cortical plasticity might play a role in the pathophysiology of patients with MDD. We used Transcranial Magnetic Stimulation (TMS) to assess inhibitory neurotransmission and cortical plasticity in the motor cortex of MDD patients and controls.

METHODS

We measured the cortical silent period (CSP) and short interval cortical inhibition (SICI), as well as intermittent theta-burst stimulation (iTBS), in 9 drug-free MDD inpatients and 18 controls.

RESULTS

The overall response to the CSP, SICI, and iTBS paradigms was not significantly different between the patient and control groups. iTBS induction resulted in significant potentiation after 20 mins in the control group (t ₍₁₇₎ = -2.8, p = 0.01), whereas no potentiation was observed in patients.

CONCLUSIONS

Potentiation of MEP amplitudes was not observed within the MDD group. No evidence was found for medium-to-large effect size differences in CSP and SICI measures in severely depressed drug-free patients, suggesting that reduced cortical inhibition is unlikely to be a robust correlate of the pathophysiological mechanism in MDD. However, these findings should be interpreted with caution due to the high inter-subject variability and the small sample size.

SIGNIFICANCE

These findings advance our understanding of neurophysiological functioning in drug-free severely depressed inpatients.

Glutamatergic System in Depression and Its Role in Neuromodulatory Techniques Optimization

Depressive disorders are among the most common psychiatric conditions and contribute to significant morbidity. Even though the use of antidepressants revolutionized the management of depression and had a tremendous positive impact on the patient's outcome, a significant proportion of patients with major depressive disorder (MDD) show no or partial or response even with adequate treatment. Given the limitations of the prevailing monoamine hypothesis-based pharmacotherapy, glutamate and glutamatergic related pathways may offer an alternative and a complementary option for designing novel intervention strategies. Over the past few decades, there has been a growing interest in understanding the neurobiological underpinnings of glutamatergic dysfunctions in the pathogenesis of depressive disorders and the development of new pharmacological and non-pharmacological treatment options. There is a growing body of evidence for the efficacy of neuromodulation techniques, including transcranial magnetic stimulation, transcutaneous direct current stimulation, transcranial alternating current stimulation, and photo-biomodulation on improving connectivity and neuroplasticity associated with depression. This review attempts to revisit the role of glutamatergic neurotransmission in the etiopathogenesis of depressive disorders and review the current neuroimaging, neurophysiological and clinical evidence of these neuromodulation techniques in the pathophysiology and treatment of depression.

Transcranial ultrasound stimulation of the human motor cortex

It has been 40 years since the report of long-term synaptic plasticity on the rodent brain. Transcranial ultrasound stimulation (TUS) shows advantages in spatial resolution and penetration depth when compared with electrical or magnetic stimulation. The repetitive TUS (rTUS) can induce cortical excitability alteration on animals, and persistent aftereffects were observed. However, the effects of rTUS on synaptic plasticity in humans remain unelucidated. In the current study, we applied a 15-min rTUS protocol to stimulate left primary motor cortex (l-M1) in 24 male healthy participants. The single-pulsed transcranial magnetic stimulation-evoked motor evoked potential and Stop-signal task was applied to measure the rTUS aftereffects. Here, we report that conditioning the human motor cortex using rTUS may produce long-lasting and statistically significant effects on motor cortex excitability as well as motor behavior, without harmful side effects observed. These findings suggest a considerable potential of rTUS in cortical plasticity modulation and clinical intervention for impulsivity-related disorders.

Do Brain-Derived Neurotrophic Factor Genetic Polymorphisms Modulate the Efficacy of Motor Cortex Plasticity Induced by Non-invasive Brain Stimulation? A Systematic Review

Techniques of non-invasive brain stimulation (NIBS) of the human primary motor cortex (M1) are widely used in basic and clinical research to induce neural plasticity. The induction of neural plasticity in the M1 may improve motor performance ability in healthy individuals and patients with motor deficit caused by brain disorders. However, several recent studies revealed that various NIBS techniques yield high interindividual variability in the response, and that the brain-derived neurotrophic factor (BDNF) genotype (i.e., Val/Val and Met carrier types) may be a factor contributing to this variability. Here, we conducted a systematic review of all published studies that investigated the effects of the BDNF genotype on various forms of NIBS techniques applied to the human M1. The motor-evoked potential (MEP) amplitudes elicited by single-pulse transcranial magnetic stimulation (TMS), which can evaluate M1 excitability, were investigated as the main outcome. A total of 1,827 articles were identified, of which 17 (facilitatory NIBS protocol, 27 data) and 10 (inhibitory NIBS protocol, 14 data) were included in this review. More than two-thirds of the data (70.4–78.6%) on both NIBS protocols did not show a significant genotype effect of NIBS on MEP changes. Conversely, most of the remaining data revealed that the Val/Val type is likely to yield a greater MEP response after NIBS than the Met carrier type in both NIBS protocols (21.4–25.9%). Finally, to aid future investigation, we discuss the potential effect of the BDNF genotype based on mechanisms and methodological issues.

Low-Dose Augmentation With Buprenorphine for Treatment-Resistant Depression: A Multisite Randomized Controlled Trial With Multimodal Assessment of Target Engagement

Background

The experimental therapeutics approach that combines a placebo-controlled clinical trial with translational neuroscience methods can provide a better understanding of both the clinical and physiological effects of pharmacotherapy. We aimed to test the efficacy and tolerability of low-dose augmentation with buprenorphine (BPN) for treatment-resistant depression, combined with multimodal assessment of target engagement.

Methods

In this multisite randomized clinical trial, 85 participants ≥50 years of age with a major depressive episode that had not responded to venlafaxine extended release were randomized to augmentation with BPN or placebo for 8 weeks. The primary outcome measure was the Montgomery-Åsberg Depression Rating Scale. In addition, three linked experiments were conducted to test target engagement: 1) functional magnetic resonance imaging using the monetary incentive delay task, 2) brain positron emission tomography of healthy participants using a novel kappa opioid receptor antagonist tracer [¹¹C]LY2795050, and 3) transcranial magnetic stimulation measure of cortical transmission after daily BPN administration.

Results

The mean ± SD dosage of BPN was 0.59 ± 0.33 mg/day. There were no significant differences between the BPN and placebo groups in Montgomery-Åsberg Depression Rating Scale changes over time or adverse effects. BPN administration had minimal effects on functional magnetic resonance imaging blood oxygen level-dependent responses in regions involved in reward anticipation and response, no significant displacement of kappa opioid receptor radioligand in positron emission tomography imaging, and no significant changes in transcranial magnetic stimulation measures of inhibitory and excitatory cortical transmission.

Conclusions

Our findings suggest a lack of clinical effect of low-dose BPN augmentation and lack of target engagement with this dosage and physiological probes.

Telomeres: the role of shortening and senescence in major depressive disorder and its therapeutic implications

Major depressive disorder (MDD) is one of the most prevalent and debilitating psychiatric disorders, with a large number of patients not showing an effective therapeutic response to available treatments. Several biopsychosocial factors, such as stress in childhood and throughout life, and factors related to biological aging, may increase the susceptibility to MDD development. Included in critical biological processes related to aging and underlying biological mechanisms associated with MDD is the shortening of telomeres and changes in telomerase activity. This comprehensive review discusses studies that assessed the length of telomeres or telomerase activity and function in peripheral blood cells and brain tissues of MDD individuals. Also, results from in vitro protocols and animal models of stress and depressive-like behaviors were included. We also expand our discussion to include the role of telomere biology as it relates to other relevant biological mechanisms, such as the hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, inflammation, genetics, and epigenetic changes. In the text and the discussion, conflicting results in the literature were observed, especially considering the size of telomeres in the central nervous system, on which there are different protocols with divergent results in the literature. Finally, the context of this review is considering cell signaling, transcription factors, and neurotransmission, which are involved in MDD and can be underlying to senescence, telomere shortening, and telomerase functions.

Paired associative stimulations: Novel tools for interacting with sensory and motor cortical plasticity

In the early 2000s, a novel non-invasive brain stimulation protocol, the paired associative stimulation (PAS), was introduced, allowing to induce and investigate Hebbian associative plasticity within the humans' motor system, with patterns resembling spike-timing-dependent plasticity properties found in cellular models. Since this evidence, PAS efficacy has been proved in healthy, and to a lesser extent, in clinical populations. Recently, novel 'modified' protocols targeting sensorimotor and crossmodal networks appeared in the literature. In the present work, we have reviewed recent advances using these 'modified' PAS protocols targeting sensory and motor cortical networks. To better categorize them, we propose a novel classification according to the nature of the peripheral and cortical stimulations (i.e., within-system, cross-systems, and cortico-cortical PAS). For each protocol of the categories mentioned above, we describe and discuss their main features, how they have been used to study and promote brain plasticity, and their advantages and disadvantages. Overall, current evidence suggests that these novel non-invasive brain stimulation protocols represent very promising tools to study the plastic properties of humans' sensorimotor and crossmodal networks, both in the healthy and in the damaged central nervous system.

Is tDCS a potential first line treatment for major depression?

Transcranial direct current stimulation (tDCS) is a novel treatment option for major depression which could be provided as a first-line treatment. tDCS is a non-invasive form of transcranial stimulation which changes cortical tissue excitability by applying a weak (0.5-2 mA) direct current via scalp electrodes. Anodal and cathodal stimulation leads to depolarisation and hyperpolarisation, respectively, and cumulative effects are observed with repeated sessions. The montage in depression most often involves anodal stimulation to the left dorsolateral prefrontal cortex. Rates of clinical response, remission, and improvements in depressive symptoms following a course of active tDCS are greater in comparison to a course of placebo sham-controlled tDCS. In particular, the largest treatment effects are evident in first episode and recurrent major depression, while minimal effects have been observed in treatment-resistant depression. The proposed mechanism is neuroplasticity at the cellular and molecular level. Alterations in neural responses have been found at the stimulation site as well as subcortically in prefrontal-amygdala connectivity. A possible mediating effect could be cognitive control in emotion dysregulation. Additional beneficial effects on cognitive impairments have been reported, which would address an important unmet need. The tDCS device is portable and can be used at home. Clinical trials are required to establish the efficacy, feasibility and acceptability of home-based tDCS treatment and mechanisms.

Insights into the Pathophysiology of Psychiatric Symptoms in Central Nervous System Disorders: Implications for Early and Differential Diagnosis

Different psychopathological manifestations, such as affective, psychotic, obsessive-compulsive symptoms, and impulse control disturbances, may occur in most central nervous system (CNS) disorders including neurodegenerative and neuroinflammatory diseases. Psychiatric symptoms often represent the clinical onset of such disorders, thus potentially leading to misdiagnosis, delay in treatment, and a worse outcome. In this review, psychiatric symptoms observed along the course of several neurological diseases, namely Alzheimer’s disease, fronto-temporal dementia, Parkinson’s disease, Huntington’s disease, and multiple sclerosis, are discussed, as well as the involved brain circuits and molecular/synaptic alterations. Special attention has been paid to the emerging role of fluid biomarkers in early detection of these neurodegenerative diseases. The frequent occurrence of psychiatric symptoms in neurological diseases, even as the first clinical manifestations, should prompt neurologists and psychiatrists to share a common clinico-biological background and a coordinated diagnostic approach.

D-cycloserine normalizes long-term motor plasticity after transcranial magnetic intermittent theta-burst stimulation in major depressive disorder

OBJECTIVES

Major Depressive Disorder (MDD) is associated with glutamatergic alterations, including the N-methyl-D-aspartate receptor (NMDA-R). The NMDA-R plays an important role in synaptic plasticity, and individuals with MDD have been shown to have impairments in repetitive Transcranial Magnetic Stimulation (rTMS) motor plasticity. Here, we test whether D-cycloserine, a NMDA-R partial agonist, can rescue TMS motor plasticity in MDD.

METHODS

We conducted randomized double-blind placebo-controlled crossover studies in healthy (n = 12) and MDD (n = 12) participants. We stimulated motor cortex using TMS intermittent theta burst stimulation (iTBS) with placebo or D-cycloserine (100 mg). Motor evoked potentials (MEPs) were sampled before and after iTBS. Stimulus response curves (SRC) were characterized at baseline, +90 minutes, and the following day.

RESULTS

Acute iTBS MEP facilitation is reduced in MDD and is not rescued by D-cycloserine. After iTBS, SRCs shift to indicate sustained decrease in excitability in healthy participants, yet increased in excitability in MDD participants. D-cycloserine normalized SRC changes from baseline to the following day in MDD participants. In both healthy and MDD participants, D-cycloserine stabilized changes in SRC.

CONCLUSION

MDD is associated with alterations in motor plasticity that are rescued and stabilized by NMDA-R agonism.

SIGNIFICANCE

Agonism of NMDA receptors rescues iTBS motor plasticity in MDD.

Neuropsychiatric Complications after Stroke

Neuropsychiatric disturbances represent a common and uniquely challenging consequence of stroke. These disorders arise at the intersection of lesion-related brain dysfunction and psychological distress related to the event and its aftermath, making it difficult to identify what symptom is a direct physiological consequence of the stroke. Depression, anxiety, fatigue, apathy, emotionalism, and anger are the most common of these syndromes, and posttraumatic stress disorder related to the stroke event has become increasingly recognized as a relevant entity. Mania, obsessive-compulsive disorder, and psychosis are less commonly encountered but potentially highly debilitating conditions that may be underrecognized. Early identification and treatment may mitigate functional impairment and improve quality of life. Evidence-based guidelines from the general population are often relied upon to guide treatment. Further research is needed to understand and tailor treatment of these disorders in the poststroke population.

Cortical inhibition, facilitation and plasticity in late-life depression: effects of venlafaxine pharmacotherapy

BACKGROUND

Late-life depression is often associated with non-response or relapse following conventional antidepressant treatment. The pathophysiology of late-life depression likely involves a complex interplay between aging and depression, and may include abnormalities in cortical inhibition and plasticity. However, the extent to which these cortical processes are modifiable by antidepressant pharmacotherapy is unknown.

METHODS

Sixty-eight patients with late-life depression received 12 weeks of treatment with open-label venlafaxine, a serotonin-norepinephrine reuptake inhibitor (≤ 300 mg/d). We combined transcranial magnetic stimulation of the left motor cortex with electromyography recordings from the right hand to measure cortical inhibition using contralateral cortical silent period and paired-pulse short-interval intracortical inhibition paradigms; cortical facilitation using a paired-pulse intracortical facilitation paradigm; and short-term cortical plasticity using a paired associative stimulation paradigm. All measures were collected at baseline, 1 week into treatment (n = 23) and after approximately 12 weeks of treatment.

RESULTS

Venlafaxine did not significantly alter cortical inhibition, facilitation or plasticity after 1 or 12 weeks of treatment. Improvements in depressive symptoms during treatment were not associated with changes in cortical physiology.

LIMITATIONS

The results presented here are specific to the motor cortex. Future work should investigate whether these findings extend to cortical areas more closely associated with depression, such as the dorsolateral prefrontal cortex.

CONCLUSION

These findings suggest that antidepressant treatment with venlafaxine does not exert meaningful changes in motor cortical inhibition or plasticity in late-life depression. The absence of changes in motor cortical physiology, alongside improvements in depressive symptoms, suggests that age-related changes may play a role in previously identified abnormalities in motor cortical processes in latelife depression, and that venlafaxine treatment does not target these abnormalities.

Physical Activity Reduces Clinical Symptoms and Restores Neuroplasticity in Major Depression

Major depressive disorder (MDD) is the most common mental disorder and deficits in neuroplasticity are discussed as one pathophysiological mechanism. Physical activity (PA) enhances neuroplasticity in healthy subjects and improves clinical symptoms of MDD. However, it is unclear whether this clinical effect of PA is due to restoring deficient neuroplasticity in MDD. We investigated the effect of a 3-week PA program applied on clinical symptoms, motor excitability and plasticity, and on cognition in patients with MDD (N = 23), in comparison to a control intervention (CI; N = 18). Before and after the interventions, the clinical symptom severity was tested using self- (BDI-II) and investigator- (HAMD-17) rated scales, transcranial magnetic stimulation (TMS) protocols were used to test motor excitability and paired-associative stimulation (PAS) to test long-term-potentiation (LTP)-like plasticity. Additionally, cognitive functions such as attention, working memory and executive functions were tested. After the interventions, the BDI-II and HAMD-17 decreased significantly in both groups, but the decrease in HAMD-17 was significantly stronger in the PA group. Cognition did not change notably in either group. Motor excitability did not differ between the groups and remained unchanged by either intervention. Baseline levels of LTP-like plasticity in the motor cortex were low in both groups (PA: 113.40 ± 2.55%; CI: 116.83 ± 3.70%) and increased significantly after PA (155.06 ± 10.48%) but not after CI (122.01 ± 4.1%). Higher baseline BDI-II scores were correlated with lower levels of neuroplasticity. Importantly, the more the BDI-II score decreased during the interventions, the stronger did neuroplasticity increase. The latter effect was particularly strong after PA (r = -0.835; p < 0.001). The level of neuroplasticity related specifically to the psychological/affective items, which are tested predominantly in the BDI-II. However, the significant clinical difference in the intervention effects was shown in the HAMD-17 which focuses more on somatic/neurovegetative items known to improve earlier in the course of MDD. In summary, PA improved symptoms of MDD and restored the deficient neuroplasticity. Importantly, both changes were strongly related on the individual patients' level, highlighting the key role of neuroplasticity in the pathophysiology and the clinical relevance of neuroplasticity-enhancing interventions for the treatment of MDD.

Transcranial magnetic stimulation neurophysiology of patients with major depressive disorder: a systematic review and meta-analysis

Major depressive disorder (MDD) is a mental illness with high socio-economic burden, but its pathophysiology has not been fully elucidated. Recently, the cortical excitatory and inhibitory imbalance hypothesis and neuroplasticity hypothesis have been proposed for MDD. Although several studies have examined the neurophysiological profiles in MDD using transcranial magnetic stimulation (TMS), a meta-analysis of TMS neurophysiology has not been performed. The objective of this study was to compare TMS-electromyogram (TMS-EMG) findings between patients with MDD and healthy controls (HCs). To this end, we examined whether patients with MDD have lower short-interval cortical inhibition (SICI) which reflects gamma-aminobutyric acid (GABA)A receptor-mediated activity, lower cortical silent period (CSP) which represents GABAB receptor-mediated activity, higher intracortical facilitation (ICF) which reflects glutamate N-methyl-D-aspartate receptor-mediated activity, and the lower result of paired associative stimulation (PAS) paradigm which shows the level of neuroplasticity in comparison with HC. Further, we explored the effect of clinical and demographic factors that may influence TMS neurophysiological indices. We first searched and identified research articles that conducted single- or paired-pulse TMS-EMG on patients with MDD and HC. Subsequently, we extracted the data from the included studies and meta-analyzed the data with the comprehensive meta-analysis software. Patients with MDD were associated with lower SICI, lower CSP, potentially higher ICF, and lower PAS compared with HC. Our results confirmed the proposed hypotheses, suggesting the usefulness of TMS neurophysiology as potential diagnostic markers of MDD.

Indices of cortical plasticity after therapeutic sleep deprivation in patients with major depressive disorder

BACKGROUND

Therapeutic sleep deprivation (SD) presents a unique paradigm to study the neurobiology of major depressive disorder (MDD). However, the rapid antidepressant mechanism, which differs from today's slow first-line treatments, is not sufficiently understood. We recently integrated two prominent hypotheses of MDD and sleep, the synaptic plasticity hypothesis of MDD and the synaptic homeostasis hypothesis of sleep-wake regulation, into a synaptic plasticity model of therapeutic SD in MDD. Here, we further tested this model positing that homeostatically elevating net synaptic strength through therapeutic SD shifts the initially deficient inducibility of associative synaptic long-term potentiation (LTP)-like plasticity in patients with MDD into a more favorable window of associative plasticity.

METHODS

We used paired associative stimulation (PAS), a transcranial magnetic stimulation protocol (TMS), to quantify cortical LTP-like plasticity after one night of therapeutic sleep deprivation in 28 patients with MDD.

RESULTS

We demonstrate a significantly different inducibility of associative plasticity in clinical responders to therapeutic SD (> 50% improvement on the 6-item Hamilton-Rating-Scale for Depression, n=13) compared to non-responders (n=15), which was driven by a long-term depression (LTD)-like response in SD-non-responders. Indices of global net synaptic strength (wake EEG theta activity, intracortical inhibition and BDNF serum levels) were increased after SD in both groups, with responders showing a generally lower intracortical inhibition than non-responders.

LIMITATIONS

Repetitive assessments prior to and after treatment would be needed to further determine potential mechanisms.

CONCLUSION

After a night of therapeutic SD, clinical responders show a significantly higher inducibility of associative LTP-like plasticity than non-responders.

Impaired LTD-like motor cortical plasticity in female patients with major depression disorder

BACKGROUNDS

Long-term depression (LTD) is a form of physiologic plasticity that is important for reversal learning and may be linked to major depression. Few studies have examined LTP-like plasticity in patients with depression. It is unclear if continuous theta burst stimulation (cTBS) induced LTD is altered in depression patients.

METHODS

Here we recruited 29 healthy control subjects and 31 female patients with depression. We performed cTBS protocol on left motor cortex and employed motor evoked potentials (MEPs) response to measure LTD-like plasticity. Peripheral molecules were measured for correlation analyses to cortical plasticity.

RESULTS

Our results revealed persistent LTD-like plasticity deficits in female patients with depression. LTD-like plasticity was impaired in patients with depression despite the fact that peripheral concentrations of BDNF were comparable to that of healthy subjects.

CONCLUSIONS

Our findings provide evidence for impaired LTD-like plasticity in patients with depression which may be an important mechanism linked to the pathophysiology and treatment of this disorder.

Time is of the essence: Coupling sleep-wake and circadian neurobiology to the antidepressant effects of ketamine

Several studies have demonstrated the effectiveness of ketamine in rapidly alleviating depression and suicidal ideation. Intense research efforts have been undertaken to expose the precise mechanism underlying the antidepressant action of ketamine; however, the translation of findings into new clinical treatments has been slow. This translational gap is partially explained by a lack of understanding of the function of time and circadian timing in the complex neurobiology around ketamine. Indeed, the acute pharmacological effects of a single ketamine treatment last for only a few hours, whereas the antidepressant effects peak at around 24 hours and are sustained for the following few days. Numerous studies have investigated the acute and long-lasting neurobiological changes induced by ketamine; however, the most dramatic and fundamental change that the brain undergoes each day is rarely taken into consideration. Here, we explore the link between sleep and circadian regulation and rapid-acting antidepressant effects and summarize how diverse phenomena associated with ketamine's antidepressant actions - such as cortical excitation, synaptogenesis, and involved molecular determinants - are intimately connected with the neurobiology of wake, sleep, and circadian rhythms. We review several recently proposed hypotheses about rapid antidepressant actions, which focus on sleep or circadian regulation, and discuss their implications for ongoing research. Considering these aspects may be the last piece of the puzzle necessary to gain a more comprehensive understanding of the effects of rapid-acting antidepressants on the brain.

Brain Response Induced with Paired Associative Stimulation Is Related to Repetition Suppression of Motor Evoked Potential

Repetition suppression (RS), i.e., the reduction of neuronal activity upon repetition of an external stimulus, can be demonstrated in the motor system using transcranial magnetic stimulation (TMS). We evaluated the RS in relation to the neuroplastic changes induced by paired associative stimulation (PAS). An RS paradigm, consisting of 20 trains of four identical suprathreshold TMS pulses 1 s apart, was assessed for motor-evoked potentials (MEPs) in 16 healthy subjects, before and following (at 0, 10, and 20 min) a common PAS protocol. For analysis, we divided RS into two components: (1) the ratio of the second MEP amplitude to the first one in RS trains, i.e., the “dynamic” component, and (2) the mean of the second to fourth MEP amplitudes, i.e., the “stable” component. Following PAS, five subjects showed change in the dynamic RS component. However, nearly all the individuals (n = 14) exhibited change in the stable component (p < 0.05). The stable component was similar between subjects showing increased MEPs and those showing decreased MEPs at this level (p = 0.254). The results suggest the tendency of the brain towards a stable state, probably free from the ongoing dynamics, following PAS.

Thymoquinone harbors protection against Concanavalin A-induced behavior deficit in BALB/c mice model

Global health estimates indicated approximately 322 million people living with depression. Rising cost of depressive illness treatment and non-responsiveness to existing therapies demand continued research to explore new and more potent therapies. Exploring the potential of natural compounds for their potent antidepressant potentials is becoming topic of interest for scientists. Anti-inflammatory activity of thymoquinone, the active ingredient of Nigella sativa, has been well documented. Current study tested thymoquinone for its antidepressant effect in a Concanavalin A (Con A)-induced depressive-like behavior in BALB/c mice. Thymoquinone successfully protected against Con A-induced behavioral despair and anxiety-like behavior. Reduced grooming behavior as a function of Con A treatment, was also reinstated. Underlying mechanism responsible for antidepressant activity of thymoquinone was analyzed by molecular docking. Thymoquinone interacts in halogen-binding pocket (HBP) of serotonin reuptake transporter indicating its potential as serotonin reuptake inhibitor. Results of current study anticipate thymoquinone as a potential antidepressant drug candidate. PRACTICAL APPLICATIONS: Black seeds of Nigella sativa are consumed with traditional and religious reference since centuries. Thymoquinone, active, and abundant component of Nigella sativa, has shown positive effects in multiple studies against arthritis, asthma, hepatic injury, neurodegeneration, and cancer owing to its immunomodulatory and anti-inflammatory attributes. Considering inflammation as one of central components involved in pathophysiology of major depressive disorder, thymoquinone has been evaluated in current study for its antidepressant potential. Positive results of current study propose thymoquinone as an affordable, natural antidepressant drug candidate with better safety profile than currently available antidepressant regimes. Thymoquinone might provide benefits against inflammation-related sickness behavior that is associated with poorer outcome of clinical depression, thus, paving the way for effective drug development against treatment-resistant depression.

Neurocognitive effects of transcranial direct current stimulation (tDCS) in unipolar and bipolar depression: Findings from an international randomized controlled trial

OBJECTIVE

Transcranial direct current stimulation (tDCS) has been found to have antidepressant effects and may have beneficial neurocognitive effects. However, prior research has produced an unclear understanding of the neurocognitive effects of repeated exposure to tDCS. The study's aim was to determine the neurocognitive effects following tDCS treatment in participants with unipolar or bipolar depression.

METHOD

The study was a triple-masked, randomized, controlled clinical trial across six international academic medical centers. Participants were randomized to high dose (2.5 mA for 30 min) or low dose (0.034 mA, for 30 min) tDCS for 20 sessions over 4 weeks, followed by an optional 4 weeks of open-label high dose treatment. The tDCS anode was centered over the left dorsolateral prefrontal cortex at F3 (10/20 EEG system) and the cathode over F8. Participants completed clinical and neurocognitive assessments before and after tDCS. Genotype (BDNF Val66Met and catechol-o-methyltransferase [COMT] Val158Met polymorphisms) were explored as potential moderators of neurocognitive effects.

RESULTS

The study randomized 130 participants. Across the participants, tDCS treatment (high and low dose) resulted in improvements in verbal learning and recall, selective attention, information processing speed, and working memory, which were independent of mood effects. Similar improvements were observed in the subsample of participants with bipolar disorder. There was no observed significant effect of tDCS dose. However, BDNF Val66Met and COMT Val158Met polymorphisms interacted with tDCS dose and affected verbal memory and verbal fluency outcomes, respectively.

CONCLUSIONS

These findings suggest that tDCS could have positive neurocognitive effects in unipolar and bipolar depression. Thus, tDCS stimulation parameters may interact with interindividual differences in BDNF and COMT polymorphisms to affect neurocognitive outcomes, which warrants further investigation.

Gene expression in peripheral blood in treatment-free major depression

BACKGROUND

Peripheral gene expression of several molecular pathways has been studied in major depressive disorder (MDD) with promising results. We sought to investigate some of these genes in a treatment-free Latino sample of Mexican descent.

MATERIAL AND METHODS

The sample consisted of 50 MDD treatment-free cases and 50 sex and age-matched controls. Gene expression of candidate genes of neuroplasticity (BDNF, p11, and VGF), inflammation (IL1A, IL1B, IL4, IL6, IL7, IL8, IL10, MIF, and TNFA), the canonical Wnt signaling pathway (TCF7L2, APC, and GSK3B), and mTOR, was compared in cases and controls. RNA was obtained from blood samples. We used bivariate analyses to compare subjects versus control mean mRNA quantification of target genes and lineal regression modelling to test for effects of age and body mass index on gene expression.

RESULTS

Most subjects were female (66%) with a mean age of 26.7 (SD 7.9) years. Only GSK3B was differentially expressed between cases and controls at a statistically significant level (p = 0.048). TCF7L-2 showed the highest number of correlations with MDD-related traits, yet these were modest in size.

DISCUSSION

GSK3B encodes a moderator of the canonical Wnt signaling pathway. It has a role in neuroplasticity, neuroprotection, depression, and other psychiatric phenotypes. We found that adding population diversity has the potential to elicit distinct peripheral gene expression markers in MDD and MDD-related traits. However, our results should only be considered as hypothesis-generating research that merits further replication in larger cohorts of similar ancestry.

Transcranial Random Noise Stimulation for the Acute Treatment of Depression: A Randomized Controlled Trial

BACKGROUND

Transcranial electrical stimulation has broad potential as a treatment for depression. Transcranial random noise stimulation, which delivers randomly fluctuating current intensities, may have greater cortical excitatory effects compared with other forms of transcranial electrical stimulation. We therefore aimed to investigate the antidepressant efficacy of transcranial random noise stimulation.

METHODS

Depressed participants were randomly assigned by computer number generator to receive 20 sessions of either active or sham transcranial random noise stimulation over 4 weeks in a double-blinded, parallel group randomized-controlled trial. Transcranial random noise stimulation was delivered for 30 minutes with a direct current offset of 2 mA and a random noise range of 2 mA. Primary analyses assessed changes in depression severity using the Montgomery-Asperg Depression Rating Scale. Neuroplasticity, neuropsychological, and safety outcomes were analyzed as secondary measures.

RESULTS

Sixty-nine participants were randomized, of which 3 discontinued treatment early, leaving 66 (sham n = 34, active n = 32) for per-protocol analysis. Depression severity scores reduced in both groups (Montgomery-Asperg Depression Rating Scale reduction in sham = 7.0 [95% CI = 5.0-8.9]; and active = 5.2 [95% CI = 3.2-7.3]). However, there were no differences between active and sham groups in the reduction of depressive symptoms or the number of participants meeting response (sham = 14.7%; active = 3.1%) and remission criteria (sham = 5.9%; active = 0%). Erythema, paresthesia, fatigue, and dizziness/light-headedness occurred more frequently in the active transcranial random noise stimulation group. Neuroplasticity, neuropsychological, and acute cognitive effects were comparable between groups.

CONCLUSION

Our results do not support the use of transcranial random noise stimulation with the current stimulation parameters as a therapeutic intervention for the treatment of depression.

CLINICAL TRIAL REGISTRATION AT CLINICALTRIALS

gov/NCT01792414.

Paired associated magnetic stimulation promotes neural repair in the rat middle cerebral artery occlusion model of stroke

Paired associative stimulation has been used in stroke patients as an innovative recovery treatment. However, the mechanisms underlying the therapeutic effectiveness of paired associative stimulation on neurological function remain unclear. In this study, rats were randomly divided into middle cerebral occlusion model (MCAO) and paired associated magnetic stimulation (PAMS) groups. The MCAO rat model was produced by middle cerebral artery embolization. The PAMS group received PAMS on days 3 to 20 post MCAO. The MCAO group received sham stimulation, three times every week. Within 18 days after ischemia, rats were subjected to behavioral experiments—the foot-fault test, the balance beam walking test, and the ladder walking test. Balance ability was improved on days 15 and 17, and the foot-fault rate was less in their affected limb on day 15 in the PAMS group compared with the MCAO group. Western blot assay showed that the expression levels of brain derived neurotrophic factor, glutamate receptor 2/3, postsynaptic density protein 95 and synapsin-1 were significantly increased in the PAMS group compared with the MCAO group in the ipsilateral sensorimotor cortex on day 21. Resting-state functional magnetic resonance imaging revealed that regional brain activities in the sensorimotor cortex were increased in the ipsilateral hemisphere, but decreased in the contralateral hemisphere on day 20. By finite element simulation, the electric field distribution showed a higher intensity, of approximately 0.4 A/m², in the ischemic cortex compared with the contralateral cortex in the template. Together, our findings show that PAMS upregulates neuroplasticity-related proteins, increases regional brain activity, and promotes functional recovery in the affected sensorimotor cortex in the rat MCAO model. The experiments were approved by the Institutional Animal Care and Use Committee of Fudan University, China (approval No. 201802173S) on March 3, 2018.

An inverse relationship between cortical plasticity and cognitive inhibition in late-life depression

Executive dysfunction is a common and disabling component of late-life depression (LLD), yet its neural mechanisms remain unclear. In particular, it is not yet known how executive functioning in LLD relates to measures of cortical physiology that may change with age and illness, namely cortical inhibition/excitation and plasticity. Here, we used transcranial magnetic stimulation (TMS) to measure cortical inhibition/excitation (n = 51), and the potentiation of cortical activity following paired associative stimulation, which is thought to reflect long-term potentiation (LTP)-like cortical plasticity (n = 32). We assessed the correlation between these measures of cortical physiology and two measures of executive functioning: cognitive inhibition, assessed using the Delis-Kaplan Executive Function System Color-Word Interference ["Stroop"] Test, and cognitive flexibility, assessed using the Trail Making Test. Correlations with recall memory and processing speed were also performed to assess the specificity of any associations to executive functioning. A significant correlation was found between greater LTP-like cortical plasticity and poorer cognitive inhibition, a core executive function (rp = -0.56, p < 0.001). We did not observe significant associations between cortical inhibition/excitation and executive functioning, or between any neurophysiological measure and cognitive flexibility, memory, or processing speed. Our finding that elevated cortical plasticity is associated with diminished cognitive inhibition emphasizes the importance of balanced synaptic strengthening to healthy cognition. More specifically, our findings suggest that hyper-excitability of cortical circuits following repeated cortical activation may promote inappropriate prepotent responses in LLD. LTP-like cortical plasticity might therefore represent a neural mechanism underlying an inhibitory control cognitive endophenotype of LLD.

Heart and soul: heart rate variability and major depression

There is a bidirectional relationship between affective disorders and cardiovascular abnormalities, often described as a downward spiral, whereas major depressive disorders (MDD, and anxiety disorders) significantly increase the risk of developing cardiovascular diseases (CVD); CVD are also associated with increased risk of developing MDD (and anxiety disorders). Moreover, the prognosis and progression of CVD is significantly worsened in the presence of MDD. Heart rate variability (HRV) has often been suggested as a potential mediator in this comorbidity. In this review, we discuss HRV alterations in MDD. However, we mainly focus on the direct relationship between HRV alterations and psychiatric symptoms, rather than its relationship with CVD, as this has been reviewed elsewhere. After a general introduction to HRV and how it can be measured, we review how HRV is altered in MDD. We subsequently describe how antidepressant drugs affect HRV, showing that some classes (such as tricyclics) generally worsen HRV, whereas others (most notably selective serotonin reuptake inhibitors) have a more positive influence. We also review the effects of several other treatments, with a special focus on vagal nerve stimulation, finishing with some further considerations and recommendation for further research, both in humans and animals.

An Integrated Model of Slow-Wave Activity and Neuroplasticity Impairments in Major Depressive Disorder

PURPOSE OF REVIEW

In this review, we aim to integrate the most recent research highlighting alterations in sleep slow-wave activity (SWA), and impairments in neuroplasticity in major depressive disorder (MDD) into a novel model of disorder maintenance.

RECENT FINDINGS

Sleep homeostasis has been shown to be impaired in MDD, with a subset of individuals also demonstrating impaired SWA. SWA is considered a marker of the homeostatic regulation of sleep, and is implicated in the downscaling of synaptic strength in the context of maintaining homeostatic plasticity. Individuals with MDD have been shown to exhibit impairments in both neural plasticity such as loss of dendritic branching, and synaptic plasticity such as decreased long-term potentiation-dependent learning and memory. Alterations in the homeostatic regulation of sleep, SWA, and synaptic plasticity in MDD suggest an underlying impairment in the modulation of synaptic strength. One candidate mechanism for this impairment is AMPA receptor trafficking.

Does depression after stroke negatively influence physical disability? A systematic review and meta-analysis of longitudinal studies

BACKGROUND

Depression after stroke is common and has been proposed to negatively affect disability by preventing optimal physical rehabilitation and recovery. However, the nature of this influence remains poorly understood. Here, we synthesise longitudinal studies to examine the hypotheses that depression after stroke (i) hampers physical rehabilitation, (ii) prevents functional improvement during recovery, and (iii) is associated with poor functional outcomes.

METHODS

A systematic literature search was conducted using the databases PubMed and Web of Science. A total of 5672 studies were screened; 28 met criteria for inclusion. The quality of included studies was assessed using the Newcastle-Ottawa Scale.

RESULTS

Individual studies showed no consistent effects of depression post-stroke on (i) the effectiveness of physical rehabilitation and (ii) functional improvements during recovery. In contrast, random-effects models revealed that (iii) depression after stroke was associated with an increased risk for poor long-term disability (OR: 2.16, 95% CI 1.70-2.77). Overall, the quality of studies was moderate and there was evidence for publication bias.

LIMITATIONS

The number of included studies was small. There was considerable methodological heterogeneity between studies, prohibiting meta-analyses for all effects of interest. Few studies examined the influence of antidepressants.

CONCLUSIONS

Depressed stroke patients are generally more disabled. However, depressed mood might not restrict improvements in physical disability during rehabilitation and recovery, although it seems to be linked to a delayed increase in the risk of poor functional outcome. High-quality evidence from longitudinal studies is needed to clarify the precise mechanisms and temporal dynamics underlying these associations.

Effects of slow-wave activity on mood disturbance in major depressive disorder

BACKGROUND

Studies have demonstrated that decreases in slow-wave activity (SWA) predict decreases in depressive symptoms in those with major depressive disorder (MDD), suggesting that there may be a link between SWA and mood. The aim of the present study was to determine if the consequent change in SWA regulation following a mild homeostatic sleep challenge would predict mood disturbance.

METHODS

Thirty-seven depressed and fifty-nine healthy adults spent three consecutive nights in the sleep laboratory. On the third night, bedtime was delayed by 3 h, as this procedure has been shown to provoke SWA. The Profile of Mood States questionnaire was administered on the morning following the baseline and sleep delay nights to measure mood disturbance.

RESULTS

Results revealed that following sleep delay, a lower delta sleep ratio, indicative of inadequate dissipation of SWA from the first to the second non-rapid eye movement period, predicted increased mood disturbance in only those with MDD.

CONCLUSIONS

These data demonstrate that in the first half of the night, individuals with MDD who have less SWA dissipation as a consequence of impaired SWA regulation have greater mood disturbance, and may suggest that appropriate homeostatic regulation of sleep is an important factor in the disorder.

Assessment of neuroplasticity in late-life depression with transcranial magnetic stimulation

BACKGROUND

Studies using Transcranial Magnetic Stimulation (TMS), a non-invasive method of brain stimulation, have implicated impaired neuroplasticity in the pathophysiology of depression in younger adults. The role of neuroplasticity in late-life depression (LLD) has not yet been explored using TMS.

OBJECTIVE

This study aimed at evaluating motor cortical neuroplasticity using paired associative stimulation (PAS). Single-pulse TMS was used to induce motor-evoked potentials (MEP) in the contralateral hand muscle before and after PAS. The potentiation of MEP amplitudes after PAS was used as an indirect index of associative plasticity and long-term potentiation (LTP) (i.e. PAS-LTP).

RESULTS

48 older adults with depression and 34 age-matched healthy controls (HC) were compared. PAS- LTP was successfully induced in 68.8% of older adults with depression and 47.1% of HC. At the group level, older adults with depression failed to show statistically significant induction of neuroplasticity, which was observed in HC. However, no significant differences were observed between the two groups for PAS-LTP.

CONCLUSION

Our results suggest that associative plasticity does not differ substantially between older adults with depression and age-matched HC. Continued research is needed to more comprehensively understand the role of neuroplasticity in the pathophysiology of LLD.