Effect of low-frequency transcranial magnetic stimulation on an affective go/no-go task in patients with major depression: role of stimulation site and depression severity

Use of transcranial magnetic stimulation (TMS) for studying cognitive control in depressed patients: A systematic review

Major depressive disorder (MDD) is a debilitating mental disorder and the leading cause of disease burden. Major depressive disorder is associated with emotional impairment and cognitive deficit. Cognitive control, which is the ability to use perceptions, knowledge, and information about goals and motivations to shape the selection of goal-directed actions or thoughts, is a primary function of the prefrontal cortex (PFC). Psychotropic medications are one of the main treatments for MDD, but they are not effective for all patients. An alternative treatment is transcranial magnetic stimulation (TMS). Previous studies have provided mixed results on the cognitive-enhancing effects of TMS treatment in patients with MDD. Some studies have found significant improvement, while others have not. There is a lack of understanding of the specific effects of different TMS protocols and stimulation parameters on cognitive control in MDD. Thus, this review aims to synthesize the effectiveness of the TMS methods and a qualitative assessment of their potential benefits in improving cognitive functioning in patients with MDD. We reviewed 21 studies in which participants underwent a treatment of any transcranial magnetic stimulation protocol, such as repetitive TMS or theta-burst stimulation. One of the primary outcome measures was any change in the cognitive control process. Overall, the findings indicate that transcranial magnetic stimulation (TMS) may enhance cognitive function in patients with MDD. Most of the reviewed studies supported the notion of cognitive improvement following TMS treatment. Notably, improvements were predominantly observed in inhibition, attention, set shifting/flexibility, and memory domains. However, fewer significant improvements were detected in evaluations of visuospatial function and recognition, executive function, phonemic fluency, and speed of information processing. This review found evidence supporting the use of TMS as a treatment for cognitive deficits in patients with MDD. The results are promising, but further research is needed to clarify the specific TMS protocol and stimulation locations that are most effective.

Cognitive functioning as predictor and marker of response to repetitive transcranial magnetic stimulation in depressive disorders: A systematic review

OBJECTIVE

Cognitive performance in Major Depressive Disorder (MDD) is frequently impaired and related to functional outcomes. Repetitive Transcranial Magnetic Stimulation (rTMS) may exert its effects on MDD acting both on depressive symptoms and neurocognition. Furthermore, cognitive status could predict the therapeutic response of depressive symptoms to rTMS. However, cognitive performances as a predictor of rTMS response in MDD has not been thoroughly investigated. This review aims to evaluate the role of pre-treatment cognitive performance as a predictor of clinical response to rTMS, and the effects of rTMS on neurocognition in MDD.

METHOD

A systematic review of studies evaluating neurocognition in MDD as an outcome and/or predictor of response to rTMS was conducted using PubMed/Medline and Embase.

RESULTS

Fifty-eight articles were identified: 25 studies included neurocognition as a predictor of response to rTMS; 56 used cognitive evaluation as an outcome of rTMS. Baseline cognitive performance and cognitive improvements after rTMS predicted clinical response to rTMS. Moreover, rTMS improved cognition in MDD.

CONCLUSIONS

Cognitive assessment could predict improvement of depression in MDD patients undergoing rTMS and help selecting patients that could have beneficial effects from rTMS. A routine cognitive assessment might stratify MDD patients and track rTMS related cognitive improvement.

The effectiveness of high-frequency left DLPFC-rTMS on depression, response inhibition, and cognitive flexibility in female subjects with major depressive disorder

BACKGROUND

The purpose of the present study was to investigate the effect of high-frequency repetitive transcranial magnetic stimulation on depression severity, response inhibition, and cognitive flexibility in subjects with major depressive disorder.

METHODS

Twenty-eight female subjects with major depressive disorder were randomly divided into experimental and control groups. High frequency (20 Hz) rTMS stimulation at 85% of the MT consisted of 25 trains of 5 s duration, a total of 2500 pulses/session or sham stimulation was applied over the left DLPFC for five consecutive days per week, for two weeks. Depression severity, response inhibition, and cognitive flexibility of subjects were assessed by Beck Depression Inventory, Go/NoGo, and Wisconsin sort cards (WCST) tests, respectively, pre- and post-TMS intervention.

RESULTS

rTMS over the left DLPFC significantly decreased the depression severity at the Beck Depression Inventory, enhanced accuracy, and decreased reaction time at the Go/NoGo task. In the Wisconsin Card Sort Test, perseverative and non-perseverative errors and failure to maintain a set index significantly decreased following rTMS treatment.

CONCLUSIONS

Findings indicate that 20-Hz rTMS treatment on the left DLPFC has a positive effect on depression severity, response inhibition, and cognitive flexibility in depressed subjects.

Instability and Uncertainty Are Critical for Psychotherapy: How the Therapeutic Alliance Opens Us Up

Tschacher and Haken have recently applied a systems-based approach to modeling psychotherapy process in terms of potentially beneficial tendencies toward deterministic as well as chaotic forms of change in the client's behavioral, cognitive and affective experience during the course of therapy. A chaotic change process refers to a greater exploration of the states that a client can be in, and it may have a potential positive role to play in their development. A distinction is made between on the one hand, specific instances of instability which are due to techniques employed by the therapist, and on the other, a more general instability which is due to the therapeutic relationship, and a key, necessary result of a successful therapeutic alliance. Drawing on Friston's systems-based model of free energy minimization and predictive coding, it is proposed here that the increase in the instability of a client's functioning due to therapy can be conceptualized as a reduction in the precisions (certainty) with which the client's prior beliefs about themselves and their world, are held. It is shown how a good therapeutic alliance (characterized by successful interpersonal synchrony of the sort described by Friston and Frith) results in the emergence of a new hierarchical level in the client's generative model of themselves and their relationship with the world. The emergence of this new level of functioning permits the reduction of the precisions of the client's priors, which allows the client to 'open up': to experience thoughts, emotions and experiences they did not have before. It is proposed that this process is a necessary precursor to change due to psychotherapy. A good consilience can be found between this approach to understanding the role of the therapeutic alliance, and the role of epistemic trust in psychotherapy as described by Fonagy and Allison. It is suggested that beneficial forms of instability in clients are an underappreciated influence on psychotherapy process, and thoughts about the implications, as well as situations in which instability may not be beneficial (or potentially harmful) for therapy, are considered.

Postpartum Stress and Neural Regulation of Emotion among First-Time Mothers

Early parenting relies on emotion regulation capabilities, as mothers are responsible for regulating both their own emotional state and that of their infant during a time of new parenting-related neural plasticity and potentially increased stress. Previous research highlights the importance of frontal cortical regions in facilitating effective emotion regulation, but few studies have investigated the neural regulation of emotion among postpartum women. The current study employed a functional neuroimaging (fMRI) approach to explore the association between perceived stress, depressive symptoms, and the neural regulation of emotion in first-time mothers. Among 59 postpartum mothers, higher perceived stress during the postpartum period was associated with less self-reported use of cognitive reappraisal in everyday life, and greater use of emotion suppression. While viewing standardized aversive images during the Emotion Regulation Task (ERT), mothers were instructed to experience their natural emotional state (Maintain) or to decrease the intensity of their negative emotion by using cognitive reappraisal (Reappraise). Whole-brain analysis revealed a two-way interaction of perceived stress x condition in the right dorsolateral prefrontal cortex (DLPFC) at p < .05 cluster-wise corrected, controlling for postpartum months and scanner type. Higher levels of perceived stress were associated with heightened right DLPFC activity while engaging in cognitive reappraisal versus naturally responding to negative stimuli. Higher right DLPFC activity during Reappraise versus Maintain was further associated with elevated parenting stress. Findings suggest that stress and everyday reappraisal use is reflected in mothers' neural regulation of emotion and may have important implications for their adaptation to parenthood.

Altered interhemispheric signal propagation in schizophrenia and depression

OBJECTIVE

Altered interhemispheric connectivity is implicated in the pathophysiology of schizophrenia (SCZ) and major depressive disorder (MDD) and may account for deficits in lateralized cognitive processes. We measured transcranial magnetic stimulation evoked interhemispheric signal propagation (ISP), a non-invasive measure of transcallosal connectivity, and hypothesized that the SCZ and MDD groups will have increased ISP compared to healthy controls.

METHODS

We evaluated ISP over the dorsolateral prefrontal cortex in 34 patients with SCZ and 34 patients with MDD compared to 32 age and sex-matched healthy controls.

RESULTS

ISP was significantly increased in patients with SCZ and patients with MDD compared to healthy controls but did not differ between patient groups. There were no effects of antidepressant, antipsychotic, and benzodiazepine medications on ISP and our results remained unchanged after re-analysis with a region of interest method.

CONCLUSION

Altered ISP was found in both SCZ and MDD patient groups. This indicates that disruptions of interhemispheric signaling processes can be indexed with ISP across psychiatric populations.

SIGNIFICANCE

These findings enhance our knowledge of the physiological mechanisms of interhemispheric imbalances in SCZ and MDD, which may serve as potential treatment targets in future patients.

Disorder- and emotional context-specific neurofunctional alterations during inhibitory control in generalized anxiety and major depressive disorder

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fMRI affective GO/NOGO tasks differentiates depression (MDD) from anxiety (GAD).

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MDD but not GAD showed impaired inhibitory control on the behavioral level.

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MDD exhibited decreased engagement of posterior frontal/mid-cingulate regions.

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The neural alterations were specific for MDD and inhibition in negative contexts.

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GAD showed intact inhibition and enhanced dlPFC activity relative to MDD.

Major Depressive Disorder (MDD) and Generalized Anxiety Disorder (GAD) are highly debilitating and often co-morbid disorders. The disorders exhibit partly overlapping dysregulations on the behavioral and neurofunctional level. The determination of disorder-specific behavioral and neurofunctional dysregulations may therefore promote neuro-mechanistic and diagnostic specificity. In order to determine disorder-specific alterations in the domain of emotion-cognition interactions the present study examined emotional context-specific inhibitory control in treatment-naïve MDD (n = 37) and GAD (n = 35) patients and healthy controls (n = 35). On the behavioral level MDD but not GAD exhibited impaired inhibitory control irrespective of emotional context. On the neural level, MDD-specific attenuated recruitment of inferior/medial parietal, posterior frontal, and mid-cingulate regions during inhibitory control were found during the negative context. GAD exhibited a stronger engagement of the left dorsolateral prefrontal cortex relative to MDD. Overall the findings from the present study suggest disorder- and emotional context-specific behavioral and neurofunctional inhibitory control dysregulations in major depression and may point to a depression-specific neuropathological and diagnostic marker.

Light-Dependent Effects of Prefrontal rTMS on Emotional Working Memory

Growing evidence suggests that colored light exposure can affect several brain functions in addition to conscious visual perception. Blue as compared to green light has especially been shown to enhance alertness and vigilance, as well as cognitive functions. However, the role of light exposure in studies using non-invasive brain stimulation remains unclear. Here, we examined the impact of light on cognitive-emotional effects of prefrontal repetitive transcranial magnetic stimulation (rTMS). In a randomized within-subjects design, twenty participants (12 males, 26 ± 4 years) were exposed to blue or green light prior and concomitant to active or sham rTMS (1Hz, 15min, 110% of the resting motor threshold), applied over the right dorsolateral prefrontal cortex (DLPFC). In each condition, an emotional working memory task (EMOBACK) was presented pre- and post-intervention. Stimuli of the EMOBACK task were positive, negative and neutral words. Our results revealed valence-specific stimulation effects in dependence of colored light exposure. More specifically, task accuracy was significantly increased for positive stimuli under blue light and for negative stimuli under green light exposure. Our findings highlight the importance of state-dependency in studies using non-invasive brain stimulation and show blue light exposure to be a potential adjunctive technique to rTMS for enhancing cognitive-emotional modulation.

Plasma Circular RNA DYM Related to Major Depressive Disorder and Rapid Antidepressant Effect Treated by Visual Cortical Repetitive Transcranial Magnetic Stimulation

BACKGROUND

Reduced plasma circular RNA DYM (circDYM) has been detected in patients with major depressive disorder (MDD). Mechanism research has demonstrated that circDYM, acting as a microRNA-9 sponge, suppressed microglial activation by increasing Heat Shock Protein 90 ubiquitination, indicating that circDYM could be a potential biomarker of MDD.

METHODS

Thirty-two normal controls (NCs) and 60 MDD patients were recruited. Enrolled patients were randomly allocated to the real or sham repetitive transcranial magnetic stimulation (rTMS) group, followed by continuous five-day visual cortical rTMS or sham treatment. All participants underwent multidimensional neuropsychological assessments and detection of circDYM levels.

RESULTS

Initial scores on all emotional and psychosocial assessments in MDD were significantly different from those of NCs. As compared with the NC group, baseline plasma circDYM levels in MDD patients decreased remarkably (p=0.030) and showed significant positive correlations with the scores of the 24-item Hamilton Depression Rating Scale (r=0.318, p=0.031) and retardation subscale (r=0.323, p=0.029). The increase in circDYM was noteworthy after rTMS (p=0.006), while downregulation with no statistical significance was observed after sham treatment (p=0.170).

LIMITATIONS

It was not estimated on the correlation between plasma circDYM levels and long-term efficacy of rTMS. The mechanism of upregulated circDYM expression in response to visual cortical rTMS remained unrevealed, and the sample size was relatively small.

CONCLUSIONS

This study verified the reduced circDYM levels in MDD patients, and further determined the upregulated circDYM expression after rTMS treatment, revealing the potential of circDYM as a biomarker for MDD diagnosis and antidepressant effect of visual cortical rTMS.

Suicidal behavior in treatment resistant major depressive disorder patients treated with transmagnetic stimulation(TMS) and its relationship with cognitive functions

The aim of this study is to investigate the effects of rTMS treatment on suicidal thoughts/behaviors and to determine the cognitive mechanisms underlying the effects of rTMS treatment on suicidal thoughts/behaviors in treatment-resistant depression(TRD). Thirty patients with TRD received rTMS 5 sessions per week for 4-6 weeks. Montgomery-Asberg Depression Rating Scale(MADRS), Columbia Suicide Severity Rating Scale(C-SSRS), Suicidal Ideation Scale(SIS), Beck Hopelessness Scale(BHS) and Cambridge Neuropsychological Test Automated Battery(CANTAB) were administered before and after treatment. After rTMS treatment, there was a significant decrease in depressive complaints and suicidal thoughts and improvement in emotional recognition. However, there was no significant change in cognitive functions such as cognitive flexibility, motor response inhibition and decision making. Pre-treatment decision-making and flexible thinking skills were related to the change in suicidal ideation. In TRD patients, rTMS has a positive effect on depressive symptoms and suicidal thoughts/behaviors and emotion recognition abilities. Although there is no negative effect on other cognitive functions, the positive effect of rTMS on cognitive functions is limited. At this point, we think that the TRD would be treated more effectively with treatments targeting specific symptom clusters such as other cognitive functions and suicidal thoughts.

Decreased Task-Related HRV Is Associated With Inhibitory Dysfunction Through Functional Inter-Region Connectivity of PFC in Major Depressive Disorder

The regulation of the autonomic nervous system (ANS) can improve cognitive function in major depressive disorders (MDD). Heart rate variability (HRV) derives from the dynamic control of the ANS and reflects the balance between the activities of the sympathetic and parasympathetic nervous systems by measuring tiny changes in adjacent heart beats. Task-related HRV may reflect the association between the flexibility of cognition and ANS function. The study was to investigate the neural mechanism of interactions between ANS and cognitive function in MDD with Magnetoencephalography (MEG) measurements. Participants included 20 MDD patients and 18 healthy controls (HCs). All participants were measured with a go/no-go task MEG. HRV indices, the standard deviation of the average normal-to-normal (NN) interval calculated over short periods (SDANN) and the square root of the mean squared differences of successive NN intervals (RMSSD), were derived from the raw MEG data. Results showed that MDD patients showed decreased SDANN and RMSSD. In MDD patients, both resting-state and task-related RMSSD were related to inhibitory and control dysfunction. In the go/no-go task, many areas in the prefrontal cortex (PFC) are responsible for an individual's inhibitory function. A brain MEG functional connectivity analysis revealed that there were significant differences in four brain regions within the prefrontal cortex (PFC) between MDD patients and HCs. Task-related RMSSD in HCs were related to the functional connectivity between the left middle frontal gyrus and the anterior cingulate cortex (ACC), while in MDD patients, these values were not related to the above functional connectivity but were related to the functional connectivity between the left middle frontal gyrus and insula. However, the resting-state RMSSD value was not related to these significant difference functional connectivity networks in all participants. It concludes that the decreased task-related HRV is associated with inhibitory dysfunction through functional inter-region connectivity in the PFC in MDD, and the task-related HRV can be used as an index of the association between MDD and autonomic dysregulation.

Prefrontal cortex executive processes affected by stress in health and disease

Prefrontal cortical executive functions comprise a number of cognitive capabilities necessary for goal directed behavior and adaptation to a changing environment. Executive dysfunction that leads to maladaptive behavior and is a symptom of psychiatric pathology can be instigated or exacerbated by stress. In this review we survey research addressing the impact of stress on executive function, with specific focus on working memory, attention, response inhibition, and cognitive flexibility. We then consider the neurochemical pathways underlying these cognitive capabilities and, where known, how stress alters them. Finally, we review work exploring potential pharmacological and non-pharmacological approaches that can ameliorate deficits in executive function. Both preclinical and clinical literature indicates that chronic stress negatively affects executive function. Although some of the circuitry and neurochemical processes underlying executive function have been characterized, a great deal is still unknown regarding how stress affects these processes. Additional work focusing on this question is needed in order to make progress on developing interventions that ameliorate executive dysfunction.

Affective Processing in Non-invasive Brain Stimulation Over Prefrontal Cortex

The prefrontal cortex (PFC) is the most frequently targeted brain region by non-invasive brain stimulation (NBS) studies. Non-invasively stimulating the PFC has been shown to both modulate affective processing and improve the clinical symptoms of several psychiatric disorders, such as depression and schizophrenia. The magnitude of the modulation depends on several factors, including the stimulation frequency, the number of stimulation sessions, and the specific sub-region of the PFC that is stimulated. Although some of the potential underlying mechanisms have been identified, the exact mechanisms that underlie these cognitive and affective changes remain unclear. The present review aims to summarize recent advances in the study of affective processing using NBS over the PFC. We will provide a theoretical framework for better understanding how affective processing changes are induced by NBS, with the goal of providing testable hypotheses for future studies.

Impact of Prefrontal Theta Burst Stimulation on Clinical Neuropsychological Tasks

Theta burst stimulation (TBS) protocols hold high promise in neuropsychological rehabilitation. Nevertheless, their ability to either decrease (continuous, cTBS) or increase (intermittent, iTBS) cortical excitability in areas other than the primary motor cortex, and their consistency modulating human behaviors with clinically relevant tasks remain to be fully established. The behavioral effects of TBS over the dorsolateral prefrontal cortex (dlPFC) are particularly interesting given its involvement in working memory (WM) and executive functions (EF), often impaired following frontal brain damage. We aimed to explore the ability of cTBS and iTBS to modulate WM and EF in healthy individuals, assessed with clinical neuropsychological tests (Digits Backward, 3-back task, Stroop Test, and Tower of Hanoi). To this end, 36 participants were assessed using the four tests 1 week prior to stimulation and immediately following a single session of either cTBS, iTBS, or sham TBS, delivered to the left dlPFC. No significant differences were found across stimulation conditions in any of the clinical tasks. Nonetheless, in some of them, active stimulation induced significant pre/post performance modulations, which were not found for the sham condition. More specifically, sham stimulation yielded improvements in the 3-back task and the Color, Color-Word, and Interference Score of the Stroop Test, an effect likely caused by task practice. Both, iTBS and cTBS, produced improvements in Digits Backward and impairments in 3-back task accuracy. Moreover, iTBS increased Interference Score in the Stroop Test in spite of the improved word reading and impaired color naming, whereas cTBS decreased the time required to complete the Tower of Hanoi. Differing from TBS outcomes reported for cortico-spinal measures on the primary motor cortex, our analyses did not reveal any of the expected performance differences across stimulation protocols. However, if one considers independently pre/post differences for each individual outcome measure and task, either one or both of the active protocols appeared to modulate WM and EF. We critically discuss the value, potential explanations, and some plausible interpretations for this set of subtle impacts of left dlPFC TBS in humans.

Decreased between-hemisphere connectivity strength and network efficiency in geriatric depression

White matter (WM) lesions have been recognized as a key etiological factor in geriatric depression. However, little is known about the topological pattern changes of WM in geriatric depression in the remitted state (RGD) and its relationship to depressive episodes. To address these questions, we acquired diffusion tensor images in 24 RGD and 24 healthy participants. Among them, 10 patients and 19 healthy controls completed a 1-year follow up. Between-hemisphere connectivity and graph theoretical methods were used to analyze the data. We found significantly reduced WM connectivity between the left and right hemisphere in the RGD group compared with the control group. Those with multiple depression episodes had greater reduction in between-hemisphere connectivity strength than those with fewer episodes. In addition, the RGD group had a reduced global clustering coefficient, global efficiency, and network strength, and an increased shortest path length compared with the controls. A lower clustering coefficient was correlated with poorer memory function. The reduction of nodal clustering coefficient, global efficiency, and network strength in several regions were associated with slower information processing speed. At 1-year follow up, the network properties in the RGD subjects were significantly changed suggesting instability of WM network properties of depressed patients. Together, our study provides direct evidence of reduced between-hemisphere WM connectivity with greater depressive episodes, and of alterations of network properties with cognitive dysfunction in geriatric depression. Hum Brain Mapp 38:53-67, 2017. © 2016 Wiley Periodicals, Inc.

Technical aspects of neurostimulation: Focus on equipment, electric field modeling, and stimulation protocols

Neuromodulation is a field of science, medicine, and bioengineering that encompasses implantable and non-implantable technologies for the purpose of improving quality of life and functioning of humans. Brain neuromodulation involves different neurostimulation techniques: transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS), which are being used both to study their effects on cognitive brain functions and to treat neuropsychiatric disorders. The mechanisms of action of neurostimulation remain incompletely understood. Insight into the technical basis of neurostimulation might be a first step towards a more profound understanding of these mechanisms, which might lead to improved clinical outcome and therapeutic potential. This review provides an overview of the technical basis of neurostimulation focusing on the equipment, the present understanding of induced electric fields, and the stimulation protocols. The review is written from a technical perspective aimed at supporting the use of neurostimulation in clinical practice.

Cortical thickness and emotion processing in young adults with mild to moderate depression: a preliminary study

BACKGROUND

Major depressive disorder (MDD) is a multifaceted illness involving cognitive, emotional, and structural brain changes; illness onset typically occurs in adolescence or young adulthood. Cortical thickness modulations may underlie, or accompany, functional brain activity changes in the prefrontal cortex (PFC) during emotional processing that tend to be observed in MDD.

METHODS

Thirteen unmedicated young adults with mild to moderate MDD, aged 18-24, completed a facial expression Go/No Go task and underwent a magnetic resonance imaging (MRI) scan to assess cortical thickness. Cortical thickness and performance on the Go/No Go task was also assessed in age-matched healthy comparison subjects (HCs; N = 14).

RESULTS

Participants with depression had thicker left pars opercularis cortices than HCs. They also exhibited impaired response inhibition to neutral faces when responding only to sad faces, and a faster response time overall.

CONCLUSIONS

Though our sample size is limited, this pilot study nevertheless provides evidence for cortical thickening in left frontal brain regions in a non-severely depressed, young adult group compared to healthy controls. There was also evidence of disturbances in emotion processing in this group.

Neuromodulation of Attentional Control in Major Depression: A Pilot DeepTMS Study

While Major Depressive Disorder (MDD) is primarily characterized by mood disturbances, impaired attentional control is increasingly identified as a critical feature of depression. Deep transcranial magnetic stimulation (deepTMS), a noninvasive neuromodulatory technique, can modulate neural activity and induce neuroplasticity changes in brain regions recruited by attentional processes. This study examined whether acute and long-term high-frequency repetitive deepTMS to the dorsolateral prefrontal cortex (DLPFC) can attenuate attentional deficits associated with MDD. Twenty-one MDD patients and 26 matched control subjects (CS) were administered the Beck Depression Inventory and the Sustained Attention to Response Task (SART) at baseline. MDD patients were readministered the SART and depressive assessments following a single session (n = 21) and after 4 weeks (n = 13) of high-frequency (20 Hz) repetitive deepTMS applied to the DLPFC. To control for the practice effect, CS (n = 26) were readministered the SART a further two times. The MDD group exhibited deficits in sustained attention and cognitive inhibition. Both acute and long-term high-frequency repetitive frontal deepTMS ameliorated sustained attention deficits in the MDD group. Improvement after acute deepTMS was related to attentional recovery after long-term deepTMS. Longer-term improvement in sustained attention was not related to antidepressant effects of deepTMS treatment.

Increased association over time between regional frontal lobe BOLD change magnitude and cardiac vagal control with sertraline treatment for major depression

Regions of the medial visceromotor network (MVN) participate in concurrently regulating shifts in both affective state and cardiac vagal control in the attentional background, and this regulatory ability may be impaired in depression. We examined whether the relationship between changes in BOLD within MVN regions and changes in cardiac vagal control (VC) during affective state shifting changed with depression treatment. Ten depressed and ten control subjects performed an emotional counting Stroop task designed to trigger affective change in the attentional background while undergoing functional magnetic resonance imaging and concurrent electrocardiography (ECG) on four occasions: week 0 (pre-treatment) and weeks 2, 6 and 12 of treatment on sertraline. We measured the absolute value of change between adjacent emotional and neutral conditions in both VC and the BOLD signal in specific regions of the MVN. Over time consistent increases were observed in BOLD-VC magnitude correlations in depressed subjects in subgenual ACC and left DLPFC, which strongly correlated with depressive symptom improvement. Symptom improvement over time was also associated with decreases in the magnitude of both BOLD shifts and VC shifts within-subjects. This suggests that as depressive symptoms improve on sertraline, subgenual ACC and DLPFC may more efficiently regulate visceral states during affective state shifting.

Future of epilepsy treatment: integration of devices

ABSTRACT 

The use of devices in the treatment of epilepsy is an emerging therapy for those patients whose seizures are not controlled by medications. This article will discuss current treatment options with devices for vagus nerve stimulation, deep brain stimulation and responsive neurostimulation. Emerging therapies in noninvasive neurostimulation such as with trigeminal nerve stimulation, transcranial magnetic stimulation and transcranial direct current stimulation may prove to be promising solutions. Finally, new and enhanced techniques of drug delivery are discussed as well as other devices with potential use in the study and treatment of epilepsy.

Repetitive transcranial magnetic stimulation over primary motor vs non-motor cortical targets; effects on experimental hyperalgesia in healthy subjects

Background

High frequency repetitive transcranial magnetic stimulation (rTMS) targetted to different cortical regions (primary motor/sensory, prefrontal) are known to alter somatosensory responses. The mechanism(s) for these effects are unclear. We compared the analgesic effects of rTMS at different cortical sites on hyperalgesia induced using topical capsaicin cream.

Methods

Fourteen healthy subjects had capsaicin cream applied to a 16 cm² area of the medial aspect of the right wrist (60 min) on 4 separate occasions over 6 weeks. rTMS (10Hz for 10s/min = 2000 stimuli @ 90% resting motor threshold of first dorsal interosseus muscle) was applied to the optimum site for right hand (M1), left dorsolateral prefrontal (DLFPC) and occipital midline (OCC) in a pseudo-randomised order. Thermal and mechanical perception and pain thresholds were determined using standardised quantitative sensory testing (QST) methods at the capsaicin site. Subjective responses to thermal stimuli (pain score on a numerical rating scale) from −2.5°C to +2.5°C of the individualised heat pain threshold (HPT) resulted in a hyperalgesia curve. Sensory testing took place prior to capsaicin application (PRE-CAP), after 30 min of capsaicin (POST-CAP) and following rTMS (30 min = POST-TMS).

Results

Capsaicin application resulted in substantial changes in thermal (but not mechanical) sensitivity to both heat and cold (eg. HPT PRE-CAP = 43.6°C to POST-CAP = 36.7°C (p < 0.001)) with no differences between groups pre-rTMS. POST-TMS HPT showed no changes for any of the treatment groups, however the pain scores for the hyperalgesia curve were significantly lower for M1 vs OCC (−24.7%, p < 0.001) and for M1 vs DLFPC (−18.3%, p < 0.02).

Conclusion

rTMS over the primary motor cortex results in a significant analgesic effect compared to other cortical areas.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-014-0166-3) contains supplementary material, which is available to authorized users.

Use of cortical stimulation in neuropathic pain, tinnitus, depression, and movement disorders

Medical treatment must strike a balance between benefit and risk. As the field of neuromodulation develops, decreased invasiveness, in combination with maintenance of efficacy, has become a goal. We provide a review of the history of cortical stimulation from its origins to the current state. The first part discusses neuropathic pain and the nonpharmacological treatment options used. The second part covers transitions to tinnitus, believed by many to be another deafferentation disorder, its classification, and treatment. The third part focuses on major depression. The fourth section concludes with the discussion of the use of cortical stimulation in movement disorders. Each part discusses the development of the field, describes the current care protocols, and suggests future avenues for research needed to advance neuromodulation.

Biological markers in noninvasive brain stimulation trials in major depressive disorder: a systematic review

OBJECTIVES

The therapeutic effects of transcranial magnetic stimulation (TMS) and transcranial direct current stimulation in patients with major depression have shown promising results; however, there is a lack of mechanistic studies using biological markers (BMs) as an outcome. Therefore, our aim was to review noninvasive brain stimulation trials in depression using BMs.

METHODS

The following databases were used for our systematic review: MEDLINE, Web of Science, Cochrane, and SCIELO. We examined articles published before November 2012 that used TMS and transcranial direct current stimulation as an intervention for depression and had BM as an outcome measure. The search was limited to human studies written in English.

RESULTS

Of 1234 potential articles, 52 articles were included. Only studies using TMS were found. Biological markers included immune and endocrine serum markers, neuroimaging techniques, and electrophysiological outcomes. In 12 articles (21.4%), end point BM measurements were not significantly associated with clinical outcomes. All studies reached significant results in the main clinical rating scales. Biological marker outcomes were used as predictors of response, to understand mechanisms of TMS, and as a surrogate of safety.

CONCLUSIONS

Functional magnetic resonance imaging, single-photon emission computed tomography, positron emission tomography, magnetic resonance spectroscopy, cortical excitability, and brain-derived neurotrophic factor consistently showed positive results. Brain-derived neurotrophic factor was the best predictor of patients' likeliness to respond. These initial results are promising; however, all studies investigating BMs are small, used heterogeneous samples, and did not take into account confounders such as age, sex, or family history. Based on our findings, we recommend further studies to validate BMs in noninvasive brain stimulation trials in MDD.

Caloric vestibular stimulation modulates affective control and mood

BACKGROUND

Clinical evidence suggests a link between vestibular dysfunctions and mood disorders. No study has yet investigated mood and affective control during vestibular stimulation in healthy participants.

OBJECTIVE

We predicted a modulating effect of caloric vestibular stimulation (CVS) on affective control measured in an affective Go/NoGo task (AGN).

METHODS

Thirty-two participants performed an AGN task while they were exposed to cold left or right ear CVS (20 °C) and sham stimulation (37 °C). In each block, either positive or negative pictures (taken from the International Affective Picture System) were defined as targets. Participants had to respond to targets (Go), and withhold responses to distractors (NoGo).

RESULTS

The sensitivity index d' (hits - false alarms) was used to measure affective control. Affective control improved during right ear CVS when viewing positive stimuli (P = .005), but decreased during left ear CVS when compared to sham stimulation (P = .009). CVS had a similar effect on positive mood ratings (Positive and Negative Affect Schedule). Positive mood ratings decreased during left ear CVS when compared to sham stimulation, but there was no effect after right ear CVS.

DISCUSSION

The results suggest that CVS, depending on side of stimulation, has a modulating effect on mood and affective control. The results complement previous findings in manic patients and provide new evidence for the clinical potential of CVS.

State-dependent effects of prefrontal repetitive transcranial magnetic stimulation on emotional working memory

BACKGROUND

A growing body of findings illustrates the importance of state-dependency in studies using brain stimulation.

OBJECTIVE

We aimed to investigate the effects of tDCS priming followed by rTMS applied over the right dorsolateral prefrontal cortex (DLPFC) on emotional working memory.

METHODS

In a randomized single-blind within-subjects design, participants performed an emotional 3-back task at baseline and after tDCS priming (anodal, cathodal) and subsequent low-frequency rTMS (active, sham) of the right DLPFC. Stimuli consisted of words related to the distinct emotion categories fear and anger as well as neutral words.

RESULTS

Task accuracy increased for fear-related words and decreased for neutral words across stimulation conditions. No general state-dependent effects of prefrontal rTMS on working memory were found. We further showed a detrimental effect of negative emotional content on working memory performance.

CONCLUSIONS

Our findings support a hemispheric lateralization of emotion processing by demonstrating that the withdrawal-related emotion fear is associated with the right DLPFC and contribute to clarifying the interaction between working memory and emotion.

Modulation of attention network activation under antidepressant agents in healthy subjects

While antidepressants are supposed to exert similar effects on mood and drive via various mechanisms of action, diverging effects are observed regarding side-effects and accordingly on neural correlates of motivation, emotion, reward and salient stimuli processing as a function of the drugs impact on neurotransmission. In the context of erotic stimulation, a unidirectional modulation of attentional functioning despite opposite effects on sexual arousal has been suggested for the selective serotonin reuptake-inhibitor (SSRI) paroxetine and the selective dopamine and noradrenaline reuptake-inhibitor (SDNRI) bupropion. To further elucidate the effects of antidepressant-related alterations of neural attention networks, we investigated 18 healthy males under subchronic administration (7 d) of paroxetine (20 mg), bupropion (150 mg) and placebo within a randomized placebo-controlled cross-over double-blind functional magnetic resonance imaging (fMRI) design during an established preceding attention task. Neuropsychological effects beyond the fMRI-paradigm were assessed by measuring alertness and divided attention. Comparing preceding attention periods of salient vs. neutral pictures, we revealed congruent effects of both drugs vs. placebo within the anterior midcingulate cortex, dorsolateral prefrontal cortex, anterior prefrontal cortex, superior temporal gyrus, anterior insula and the thalamus. Relatively decreased activation in this network was paralleled by slower reaction times in the divided attention task in both verum conditions compared to placebo. Our results suggest similar effects of antidepressant treatments on behavioural and neural attentional functioning by diverging neurochemical pathways. Concurrent alterations of brain regions within a fronto-parietal and cingulo-opercular attention network for top-down control could point to basic neural mechanisms of antidepressant action irrespective of receptor profiles.

Antidepressant effects of sertraline associated with volume increases in dorsolateral prefrontal cortex

BACKGROUND

Structural brain imaging has revealed differences in gray matter volume between depressed individuals and control subjects in key structures related to emotion. The aim of the present study was to assess within subjects whether regional changes in gray matter volume were observed over time in depressed patients treated with sertraline.

METHODS

Thirteen depressed patients were assigned to selective serotonin reuptake inhibitor (SSRI) treatment with sertraline. Structural magnetic resonance imaging (MRI) was performed at four time points over 12 weeks of treatment. Depressed individuals were compared to a control group of 10 subjects scanned at the same time points using voxel based morphometry and a statistical growth modeling technique.

RESULTS

SSRI-treated patients showed a region of significantly increasing gray matter volume over time within the left dorsolateral prefrontal cortex (DLPFC) that specifically correlated with decreases in self-reported depression levels. No statistically significant changes were observed related to time in controls.

LIMITATIONS

This study included a small sample size and the method of analysis was capable of detecting only linear changes in volume.

CONCLUSIONS

Effective antidepressant treatment with sertraline is associated with left DLPFC volume increases. These volume increases may reflect cortical architectural changes associated with top-down neuronal modulation of emotion.

Impaired interhemispheric connectivity in medication-naive patients with major depressive disorder

BACKGROUND

Abnormalities in the anterior interhemispheric connections provided by the corpus callosum (CC) have long been implicated in major depressive disorder (MDD). The purpose of this study was to investigate interhemispheric connectivity in medication-naive patients with MDD by measuring fractional anisotropy in the CC with diffusion tensor imaging (DTI) techniques.

METHODS

We obtained DTI scans from medication-naive patients with MDD and from matched healthy controls. Fractional anisotropy values were compared using semiautomatic region of interest methods to localize the regional CC differences between these 2 groups.

RESULTS

We enrolled 27 patients and 27 controls in our study. Fractional anisotropy values were significantly lower in the anterior genu of the CC in the MDD group than in the control group (p = 0.009, corrected); results were not significantly different in any other CC subregions.

LIMITATIONS

As patients with MDD were already experiencing acute episodes, future studies of individuals at risk for MDD are warranted to elucidate the interhemispheric connectivity abnormalities associated with the predisposition to MDD.

CONCLUSION

The findings demonstrate abnormalities in the structural integrity of the anterior genu of the CC in medication-naive individuals with MDD, which may contribute to impairment of interhemispheric connectivity in patients with this disorder.

Affective set-shifting deficits in patients with major depression in remission

While numerous studies have focused on neuropsychological deficits during acute depressive episodes, results have been inconsistent for patients in remission. This case-control study aimed to explore whether remitted patients show deficits in an affective shifting task that has proven sensitive to assess emotional-cognitive deficits in acute depression. 69 fully remitted depressed patients were compared with 76 matched healthy subjects in their performance of a picture-based affective shifting task. Compared to healthy subjects, remitted patients show impaired go/no-go performance during shift, but not during non-shift conditions, reflecting a specific deficit in affective set-shifting. Impaired performance concerns omissions rather than false alarms or response times and is correlated with the duration of illness, but not the number of depressive episodes, time since remission or age. Our findings suggest that affective set-shifting deficits are also present during remission of depressive symptoms. These deficits may particularly concern enhanced inhibitory control and seem to develop over the course of the illness independent of acute episodes.

Dissociation of motor task-induced cortical excitability and pain perception changes in healthy volunteers

BACKGROUND

There is evidence that interventions aiming at modulation of the motor cortex activity lead to pain reduction. In order to understand further the role of the motor cortex on pain modulation, we aimed to compare the behavioral (pressure pain threshold) and neurophysiological effects (transcranial magnetic stimulation (TMS) induced cortical excitability) across three different motor tasks.

METHODOLOGY/PRINCIPAL FINDINGS

Fifteen healthy male subjects were enrolled in this randomized, controlled, blinded, cross-over designed study. Three different tasks were tested including motor learning with and without visual feedback, and simple hand movements. Cortical excitability was assessed using single and paired-pulse TMS measures such as resting motor threshold (RMT), motor-evoked potential (MEP), intracortical facilitation (ICF), short intracortical inhibition (SICI), and cortical silent period (CSP). All tasks showed significant reduction in pain perception represented by an increase in pressure pain threshold compared to the control condition (untrained hand). ANOVA indicated a difference among the three tasks regarding motor cortex excitability change. There was a significant increase in motor cortex excitability (as indexed by MEP increase and CSP shortening) for the simple hand movements.

CONCLUSIONS/SIGNIFICANCE

Although different motor tasks involving motor learning with and without visual feedback and simple hand movements appear to change pain perception similarly, it is likely that the neural mechanisms might not be the same as evidenced by differential effects in motor cortex excitability induced by these tasks. In addition, TMS-indexed motor excitability measures are not likely good markers to index the effects of motor-based tasks on pain perception in healthy subjects as other neural networks besides primary motor cortex might be involved with pain modulation during motor training.

The use of the EEG in measuring therapeutic drug action: focus on depression and antidepressants

A major issue in proof of concept studies and early clinical trials of novel therapeutic agents is that the active drugs can often have a relatively small additional effect compared with placebo. This is especially the case in psychiatry when we usually have no direct method of measuring the pathology underlying the disorder being studied but, rather, have to rely on the subjective assessment of psychiatric symptoms. The use of the electroencephalogram (EEG) offers two potential major means of addressing this problem. First it is able to provide direct data relating to neural activity that may be abnormal in certain disorders. As such there are opportunities for utilizing the EEG in a variety of ways as an objective outcome measure. Second there is growing evidence that in certain circumstances the EEG can be used to predict which patients are likely to respond to treatment, thus potentially increasing the power of studies by decreasing non-response rates and increasing mean changes in outcome measure. Both of these uses of the EEG are illustrated in reference to the study of mood disorders and in particular depression and its treatment with antidepressants.

Fear induced neuronal alterations in a genetic model of depression: an fMRI study on awake animals

Previous human imaging studies used facial stimuli to explore the potential association between depression and fear. This study aimed at investigating brain alterations in a rodent model of depression when innate fear was induced in the form of the predator odor trimethylthiazoline (TMT). Flinders sensitive line (FSL) rats, a genetic animal model of depression, and their control counterpart Flinders resistant line (FRL), were used in this functional magnetic resonance imaging (fMRI) assessment. Compared to FRL, FSL rats exhibited greater BOLD activation in the cortical amygdala and hypoactivation in the prefrontal cortex in response to TMT, suggesting cortico-amygdalar dysfunction in the depressed strain. In addition, the hyperactivation in the insular cortex in FSL rats may be the basis for enhanced neuronal responses to fear and aversion in depression. These results are evidence for the value of translational models of depression in expanding understanding of the neural circuitries sub-serving common human co-morbidities like depression and fear.

Can a behavioral intervention enhance the effect of repetitive transcranial magnetic stimulation on mood?

BACKGROUND

One of the few novel treatments developed for major depression in recent years has been repetitive transcranial magnetic stimulation (rTMS). Despite mostly promising results, 50-60% of patients do not respond to rTMS. Therefore, it is important to investigate ways of enhancing the effectiveness of this treatment. To date, attempting to enhance the mood effects of rTMS via behavioral means has not been investigated. One such intervention involves concurrent exposure to affective stimuli that have been shown to result in activation of brain regions associated with emotion. This pilot study of ten participants investigates such an intervention.

OBJECTIVES

The aim of this pilot study was to investigate whether exposing participants to affective stimuli while they were receiving 5 Hz rTMS resulted in greater mood change compared with rTMS or affective stimuli alone.

METHODS

Ten healthy male and female participants were exposed to affective stimuli while receiving rTMS. All participants took part in three counterbalanced conditions conducted a week apart in which they received rTMS (active or sham) delivered to the left dorsolateral prefrontal cortex (DLPFC) combined with affective stimuli (positive or neutral). To measure the impact of the dual intervention visual analogue mood scales and an affective go no go task were conducted pre- and post intervention for each session.

RESULTS

There was no effect of any rTMS condition on performances on the affective go no go task, or on any of the visual analogue scales.

CONCLUSIONS

The current data do not provide support for the use of affective stimuli during rTMS. Methodological limitations that may have contributed to the lack of significant findings are discussed.

Co-occurring anxiety influences patterns of brain activity in depression

Brain activation associated with anhedonic depression and co-occurring anxious arousal and anxious apprehension was measured by fMRI during performance of an emotion word Stroop task. Consistent with EEG findings, depression was associated with rightward frontal lateralization in the dorsolateral prefrontal cortex (DLPFC), but only when anxious arousal was elevated and anxious apprehension was low. Activity in the right inferior frontal gyrus (IFG) was also reduced for depression under the same conditions. In contrast, depression was associated with more activity in the anterior cingulate cortex (dorsal ACC and rostral ACC) and the bilateral amygdala. Results imply that depression, particularly when accompanied by anxious arousal, may result in a failure to implement top-down processing by appropriate brain regions (left DLPFC, right IFG) due to increased activation in regions associated with responding to emotionally salient information (right DLPFC, amygdala).

Neuromodulation approaches for the treatment of major depression: challenges and recommendations from a working group meeting

The use of neuromodulation as a treatment for major depressive disorder (MDD) has recently attracted renewed interest due to development of other non-pharmacological therapies besides electroconvulsive therapy (ECT) such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). METHOD: We convened a working group of researchers to discuss the updates and key challenges of neuromodulation use for the treatment of MDD. RESULTS: The state-of-art of neuromodulation techniques was reviewed and discussed in four sections: [1] epidemiology and pathophysiology of MDD; [2] a comprehensive overview of the neuromodulation techniques; [3] using neuromodulation techniques in MDD associated with non-psychiatric conditions; [4] the main challenges of neuromodulation research and alternatives to overcome them. DISCUSSION: ECT is the first-line treatment for severe depression. TMS and tDCS are strategies with a relative benign profile of side effects; however, while TMS effects are comparable to antidepressant drugs for treating MDD; further research is needed to establish the role of tDCS. DBS and VNS are invasive strategies with a possible role in treatment-resistant depression. In summary, MDD is a chronic and incapacitating condition with a high prevalence; therefore clinicians should consider all the treatment options including invasive and non-invasive neuromodulation approaches.

A single session of rTMS over the left dorsolateral prefrontal cortex influences attentional control in depressed patients

Depressed patients are impaired in the ability to shift their focus of attention. This attentional control process is related to dysfunctions in the dorsolateral prefrontal cortex (DLPFC). It has been proposed that a dorsal circuit plays an important role in the interaction between emotional and attentional information processing. However, because the different emphasis of fundamental cognitive neuroscience research and clinical research of repetitive transcranial magnetic stimulation (rTMS) over the DLPFC, little research has been done on the effects of rTMS on cognitive functioning after a single stimulation session to explore the neural systems underlying depression. This study was conducted as a double-blind, placebo-controlled, crossover, within subjects design. Sixteen depressed patients performed a modified task switching paradigm, before and after receiving high frequency (HF) versus placebo rTMS over the left DLPFC. One session of HF-rTMS over the left DLPFC had a specific beneficial effect on task-switching performance, whereas mood remained stable. Antidepressant effects of rTMS could be related to the same neurochemical changes that underlie cognitive functioning. Therefore, task switching performance may provide a unique window into the extent of antidepressant effects which can be considered as second-order long-term effects possibly related to primary alternations in cognitive functioning.

Altered negative BOLD responses in the default-mode network during emotion processing in depressed subjects

Studies using functional magnetic resonance imaging (fMRI) show predominant negative blood oxygenation level-dependent (BOLD) responses (NBRs) in regions of the default-mode network such as the pregenual anterior cingulate cortex, the ventromedial prefrontal cortex, and the posterior cingulate cortex. Patients with major depressive disorder (MDD) show emotional-cognitive disturbances, which have been associated with alterations within the default-mode network. However, it remains unclear whether these default-mode network alterations are related to abnormalities in NBRs. We therefore investigated neural activity in the default-mode network during different emotional tasks in patients with MDD in an event-related fMRI design. MDD patients showed significantly reduced NBRs in several regions of the default-mode network. Decreased NBRs in MDD patients correlated with depression severity and feelings of hopelessness. In sum, our findings demonstrate that default-mode network NBRs are reduced in MDD and modulate these patients' abnormally negative emotions.

Neural mechanisms underlying drug-related cue distraction in active cocaine users

Human drug dependence routinely features a difficulty with disengaging attention from drug-related stimuli, a symptom previously shown to be predictive of relapse during treatment. We examined the neural mechanisms underlying this attentional bias in cocaine users, varying working memory (WM) load to reflect the demands imposed by ruminative craving thoughts. Sixteen active users of cocaine were administered a WM task that manipulated the requirement for selective attention by varying the background contents, cocaine-related or neutral, upon which a recall probe item was shown. Behavioural and fMRI data were collected. Cocaine users had significantly poorer attentional control under high WM demands, suffering both increased response times and reduced recall accuracy, with this effect more pronounced for cocaine stimuli (when compared to neutral stimuli). The presence of background cocaine stimuli was associated with increases in occipital cortex activity, consistent with increased visual processing of the irrelevant stimuli for these trials. In addition, the cocaine stimuli were associated with increased right prefrontal activity with those participants with higher levels of right prefrontal activity having lower levels of attentional bias. Cocaine users under high cognitive demands had difficulty modulating the neural mechanisms underlying cognitive control which appear necessary for restricting the visual processing of task-irrelevant, but salient drug-related, stimuli, a finding that may be relevant to identifying those at most risk of relapse.

Impaired interhemispheric interactions in patients with major depression

Previous studies have shown that patients with major depression have an interhemispheric imbalance between right and left prefrontal and motor cortex. We aimed to investigate the interhemispheric interactions in patients with major depression using repetitive transcranial magnetic stimulation (rTMS). Thirteen patients with major depression and 14 age-matched healthy subjects participated in this study. Corticospinal excitability before and after 1 Hz rTMS (applied to the left primary motor cortex) was assessed in the left and right motor cortex and these results were compared with those in healthy subjects. There was a significant difference in the interhemispheric effects between patients with depression and healthy subjects. In healthy subjects, 1 Hz rTMS significantly decreased corticospinal excitability in the stimulated, left hemisphere and increased it in the contralateral, right hemisphere. In depressed subjects, 1 Hz rTMS also decreased corticospinal excitability in the left hemisphere; however, it induced no significant changes in corticospinal excitability in the contralateral, right hemisphere. In addition, there was a significant correlation between the degree of interhemispheric modulation and the severity of the depression as indexed by the Beck Depression Inventory scores. Our findings showing a decreased interhemispheric modulation in patients with major depression are consistent with the notion that mood disorders are associated with slow interhemispheric switching mechanisms.

Modulating presence and impulsiveness by external stimulation of the brain

Background

"The feeling of being there" is one possible way to describe the phenomenon of feeling present in a virtual environment and to act as if this environment is real. One brain area, which is hypothesized to be critically involved in modulating this feeling (also called presence) is the dorso-lateral prefrontal cortex (dlPFC), an area also associated with the control of impulsive behavior.

Methods

In our experiment we applied transcranial direct current stimulation (tDCS) to the right dlPFC in order to modulate the experience of presence while watching a virtual roller coaster ride. During the ride we also registered electro-dermal activity. Subjects also performed a test measuring impulsiveness and answered a questionnaire about their presence feeling while they were exposed to the virtual roller coaster scenario.

Results

Application of cathodal tDCS to the right dlPFC while subjects were exposed to a virtual roller coaster scenario modulates the electrodermal response to the virtual reality stimulus. In addition, measures reflecting impulsiveness were also modulated by application of cathodal tDCS to the right dlPFC.

Conclusion

Modulating the activation with the right dlPFC results in substantial changes in responses of the vegetative nervous system and changed impulsiveness. The effects can be explained by theories discussing the top-down influence of the right dlPFC on the "impulsive system".

Imbalance between left and right dorsolateral prefrontal cortex in major depression is linked to negative emotional judgment: an fMRI study in severe major depressive disorder

BACKGROUND

Although recent neuroimaging and therapeutic transcranial magnetic cortex stimulation (TMS) studies suggest imbalance between left and right dorsolateral prefrontal cortex (DLPFC) in major depressive disorder (MDD) the fundamental neuropsychological characterization of left DLPFC hypoactivity and right DLPFC hyperactivity in MDD remains poorly understood.

METHODS

We used event-related functional magnetic resonance imaging (fMRI) to investigate neural activity in left and right DLPFC related to unattended (unexpected) and attended (expected) judgment of emotions. Participating in the study were 20 medication-free patients with MDD and 30 healthy subjects.

RESULTS

The MDD patients showed hypoactivity in the left DLPFC during both unattended and attended emotional judgment and hyperactivity in the right DLPFC during attended emotional judgment. In contrast to healthy subjects, left DLPFC activity during emotional judgment was not parametrically modulated by negative emotional valence and was inversely modulated by positive emotional valence in MDD patients. Hyperactivity in the right DLPFC correlated with depression severity.

CONCLUSIONS

Results demonstrate that left DLPFC hypoactivity is associated with negative emotional judgment rather than with emotional perception or attention while right DLPFC hyperactivity is linked to attentional modulation. Left-right DLPFC imbalance is characterized in neuropsychological regard, which bridges the gap from resting metabolism and therapeutic repetitive transcranial magnetic stimulation effects to functional neuroanatomy of altered emotional-cognitive interaction in MDD.

Go-no-go task performance improvement after anodal transcranial DC stimulation of the left dorsolateral prefrontal cortex in major depression

BACKGROUND

We recently showed that repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex (DLPFC) can affect the performance in an affective go-no-go (AGN) task. We aimed to extend this previous investigation testing whether one session of anodal transcranial direct current stimulation (tDCS) of the left DLPFC, as compared with anodal occipital and sham tDCS, affects this AGN task performance.

METHODS

Twenty-six patients with major depression were randomized to receive anodal tDCS of the left DLPFC, occipital cortex or sham tDCS (the cathode electrode was placed over the frontopolar area for the three conditions). An AGN task was performed immediately before and after treatment. Performance changes (pre and post-treatment) were compared across groups of treatment and correlated with Hamilton Depression Rating Scale (HDRS) score changes.

RESULTS

The results show that anodal stimulation of the left DLPFC was the only condition that induced a significant improvement in task performance as shown by the increase in the number of correct responses. In addition, this effect was specific for figures with positive emotional content. This performance enhancement was not correlated with mood changes after 10 days of tDCS treatment.

LIMITATIONS

Although the effects of tDCS are less focal than rTMS, it can induce a longer and stronger modulation of cortical excitability.

CONCLUSIONS

Our findings suggest that left DLPFC activity is associated with positive emotional processing, confirming and extending results of previous studies that associated right DLPFC and orbito-frontal cortex activity with emotional processing. Furthermore the effects of tDCS on mood and cognition seem to be independent in major depression. These lines of evidence together shed light on the neural circuitry involved with emotional processing in major depression.