Neurophysiological characterization of magnetic seizure therapy (MST) in non-human primates

Magnetic seizure therapy and electroconvulsive therapy increase aperiodic activity

Major depressive disorder (MDD) is a leading cause of disability worldwide. One of the most efficacious treatments for treatment-resistant MDD is electroconvulsive therapy (ECT). Recently, magnetic seizure therapy (MST) was developed as an alternative to ECT due to its more favorable side effect profile. While these approaches have been very successful clinically, the neural mechanisms underlying their therapeutic effects are unknown. For example, clinical "slowing" of the electroencephalogram beginning in the postictal state and extending days to weeks post-treatment has been observed in both treatment modalities. However, a recent longitudinal study of a small cohort of ECT patients revealed that, rather than delta oscillations, clinical slowing was better explained by increases in aperiodic activity, an emerging EEG signal linked to neural inhibition. Here we investigate the role of aperiodic activity in a cohort of patients who received ECT and a cohort of patients who received MST treatment. We find that aperiodic neural activity increases significantly in patients receiving either ECT or MST. Although not directly related to clinical efficacy in this dataset, increased aperiodic activity is linked to greater amounts of neural inhibition, which is suggestive of a potential shared neural mechanism of action across ECT and MST.

Transcranial magnetic stimulation in non-human primates: A systematic review

Transcranial magnetic stimulation (TMS) is widely employed as a tool to investigate and treat brain diseases. However, little is known about the direct effects of TMS on the brain. Non-human primates (NHPs) are a valuable translational model to investigate how TMS affects brain circuits given their neurophysiological similarity with humans and their capacity to perform complex tasks that approach human behavior. This systematic review aimed to identify studies using TMS in NHPs as well as to assess their methodological quality through a modified reference checklist. The results show high heterogeneity and superficiality in the studies regarding the report of the TMS parameters, which have not improved over the years. This checklist can be used for future TMS studies with NHPs to ensure transparency and critical appraisal. The use of the checklist would improve methodological soundness and interpretation of the studies, facilitating the translation of the findings to humans. The review also discusses how advancements in the field can elucidate the effects of TMS in the brain.

Subgenual cingulate connectivity and hippocampal activation are related to MST therapeutic and adverse effects

Aberrant connectivity between the dorsolateral prefrontal cortex (DLPFC) and the subgenual cingulate cortex (SGC) has been linked to the pathophysiology of depression. Indirect evidence also links hippocampal activation to the cognitive side effects of seizure treatments. Magnetic seizure therapy (MST) is a novel treatment for patients with treatment resistant depression (TRD). Here we combine transcranial magnetic stimulation with electroencephalography (TMS-EEG) to evaluate the effects of MST on connectivity and activation between the DLPFC, the SGC and hippocampus (Hipp) in patients with TRD. The TMS-EEG was collected from 31 TRD patients prior to and after an MST treatment trial. Through TMS-EEG methodology we evaluated significant current scattering (SCS) as an index of effective connectivity between the SGC and left DLPFC. Significant current density (SCD) was used to assess activity at the level of the Hipp. The SCS between the SGC and DLPFC was reduced after the course of MST (p < 0.036). The DLPFC-SGC effective connectivity reduction correlated with the changes in Hamilton depression score pre-to-post treatment (R = 0.46; p < 0.031). The SCD localized to the Hipp was reduced after the course of MST (p < 0.015), and the SCD change was correlated with montreal cognitive assessment (MOCA) scores pre-post the course of MST (R = -0.59; p < 0.026). Our findings suggest that MST treatment is associated with SGC-DLPFC connectivity reduction and that changes to cognition are associated with Hipp activation reduction. These findings demonstrate two distinct processes which drive efficacy and side effects separately, and might eventually aid in delineating physiological TRD targets in clinical settings.

Differences in Seizure Expression Between Magnetic Seizure Therapy and Electroconvulsive Shock

OBJECTIVE

Evidence suggests that magnetic seizure therapy (MST) results in fewer side effects than electroconvulsive treatment, both in humans treated with electroconvulsive therapy (ECT) as well as in the animal preclinical model that uses electroconvulsive shock (ECS). Evidence suggests that MST results in fewer cognitive side effects than ECT. Although MST offers enhanced control over seizure induction and spread, little is known about how MST and ECT seizures differ. Seizure characteristics are associated with treatment effect. This study presents quantitative analyses of electroencephalogram (EEG) power after electrical and magnetic seizure induction and anesthesia-alone sham in an animal model. The aim was to test whether differential neurophysiological characteristics of the seizures could be identified that support earlier observations that the powers of theta, alpha, and beta but not delta frequency bands were lower after MST when compared with those after ECS.

METHODS

In a randomized, sham-controlled trial, 24 macaca mulatte received 6 weeks of daily sessions while scalp EEG was recorded. Electroencephalogram power was quantified within delta, theta, alpha, and beta frequency bands.

RESULTS

Magnetic seizure therapy induced lower ictal expression in the theta, alpha and beta frequencies than ECS, but MST and ECS were indistinguishable in the delta band. Magnetic seizure therapy showed less postictal suppression than ECS. Increasing electrical dosage increased ictal power, whereas increasing MST dosage had no effect on EEG expression.

CONCLUSIONS

Magnetic seizure therapy seizures have less robust electrophysiological expression than ECS, and these differences are largest in the alpha and beta bands. The relevance of these differences in higher frequency bands to clinical outcomes deserves further exploration.

SIGNIFICANCE

Contrasting EEG in ECS and MST may lead to insights on the physiological underpinnings of seizure-induced amnesia and to finding ways to reduce cognitive side effects.

Minimum Electric Field Exposure for Seizure Induction with Electroconvulsive Therapy and Magnetic Seizure Therapy

Lowering and individualizing the current amplitude in electroconvulsive therapy (ECT) has been proposed as a means to produce stimulation closer to the neural activation threshold and more focal seizure induction, which could potentially reduce cognitive side effects. However, the effect of current amplitude on the electric field (E-field) in the brain has not been previously linked to the current amplitude threshold for seizure induction. We coupled MRI-based E-field models with amplitude titrations of motor threshold (MT) and seizure threshold (ST) in four nonhuman primates (NHPs) to determine the strength, distribution, and focality of stimulation in the brain for four ECT electrode configurations (bilateral, bifrontal, right-unilateral, and frontomedial) and magnetic seizure therapy (MST) with cap coil on vertex. At the amplitude-titrated ST, the stimulated brain subvolume (23-63%) was significantly less than for conventional ECT with high, fixed current (94-99%). The focality of amplitude-titrated right-unilateral ECT (25%) was comparable to cap coil MST (23%), demonstrating that ECT with a low current amplitude and focal electrode placement can induce seizures with E-field as focal as MST, although these electrode and coil configurations affect differently specific brain regions. Individualizing the current amplitude reduced interindividual variation in the stimulation focality by 40-53% for ECT and 26% for MST, supporting amplitude individualization as a means of dosing especially for ECT. There was an overall significant correlation between the measured amplitude-titrated ST and the prediction of the E-field models, supporting a potential role of these models in dosing of ECT and MST. These findings may guide the development of seizure therapy dosing paradigms with improved risk/benefit ratio.

New directions in the rational design of electrical and magnetic seizure therapies: individualized Low Amplitude Seizure Therapy (iLAST) and Magnetic Seizure Therapy (MST)

Electroconvulsive therapy remains a key treatment option for severe cases of depression, but undesirable side-effects continue to limit its use. Innovations in the design of novel seizure therapies seek to improve its risk benefit ratio through enhanced control of the focality of stimulation. The design of seizure therapies with increased spatial precision is motivated by avoiding stimulation of deep brain structures implicated in memory retention, including the hippocampus. The development of two innovations in seizure therapy-individualized low-amplitude seizure therapy (iLAST) and magnetic seizure therapy (MST), are detailed. iLAST is a method of seizure titration involving reducing current spread in the brain by titrating current amplitude from the traditional fixed amplitudes. MST, which can be used in conjunction with iLAST dosing methods, involves the use of magnetic stimulation to reduce shunting and spreading of current by the scalp occurring during electrical stimulation. Evidence is presented on the rationale for increasing the focality of ECT in hopes of preserving its effectiveness, while reducing cognitive side-effects. Finally, the value of electric field and neural modelling is illustrated to explain observed clinical effects of modifications to ECT technique, and their utility in the rational design of the next generation of seizure therapies.

Individualized Low-Amplitude Seizure Therapy: Minimizing Current for Electroconvulsive Therapy and Magnetic Seizure Therapy

Electroconvulsive therapy (ECT) at conventional current amplitudes (800-900 mA) is highly effective but carries the risk of cognitive side effects. Lowering and individualizing the current amplitude may reduce side effects by virtue of a less intense and more focal electric field exposure in the brain, but this aspect of ECT dosing is largely unexplored. Magnetic seizure therapy (MST) induces a weaker and more focal electric field than ECT; however, the pulse amplitude is not individualized and the minimum amplitude required to induce a seizure is unknown. We titrated the amplitude of long stimulus trains (500 pulses) as a means of determining the minimum current amplitude required to induce a seizure with ECT (bilateral, right unilateral, bifrontal, and frontomedial electrode placements) and MST (round coil on vertex) in nonhuman primates. Furthermore, we investigated a novel method of predicting this amplitude-titrated seizure threshold (ST) by a non-convulsive measurement of motor threshold (MT) using single pulses delivered through the ECT electrodes or MST coil. Average STs were substantially lower than conventional pulse amplitudes (112-174 mA for ECT and 37.4% of maximum device amplitude for MST). ST was more variable in ECT than in MST. MT explained 63% of the ST variance and is hence the strongest known predictor of ST. These results indicate that seizures can be induced with less intense electric fields than conventional ECT that may be safer; efficacy and side effects should be evaluated in clinical studies. MT measurement could be a faster and safer alternative to empirical ST titration for ECT and MST.

Magnetic Seizure Therapy for Unipolar and Bipolar Depression: A Systematic Review

Objective. Magnetic seizure therapy (MST) is a novel, experimental therapeutic intervention, which combines therapeutic aspects of electroconvulsive therapy (ECT) and transcranial magnetic stimulation, in order to achieve the efficacy of the former with the safety of the latter. MST might prove to be a valuable tool in the treatment of mood disorders, such as major depressive disorder (MDD) and bipolar disorder. Our aim is to review current literature on MST. Methods. OVID and MEDLINE databases were used to systematically search for clinical studies on MST. The terms "magnetic seizure therapy," "depression," and "bipolar" were employed. Results. Out of 74 studies, 8 met eligibility criteria. There was considerable variability in the methods employed and samples sizes were small, limiting the generalization of the results. All studies focused on depressive episodes, but few included patients with bipolar disorder. The studies found reported significant antidepressant effects, with remission rates ranging from 30% to 40%. No significant cognitive side effects related to MST were found, with a better cognitive profile when compared to ECT.

CONCLUSION

MST was effective in reducing depressive symptoms in mood disorders, with generally less side effects than ECT. No study focused on comparing MST to ECT on bipolar depression specifically.

Electric Field Model of Transcranial Electric Stimulation in Nonhuman Primates: Correspondence to Individual Motor Threshold

OBJECTIVE

To develop a pipeline for realistic head models of nonhuman primates (NHPs) for simulations of noninvasive brain stimulation, and use these models together with empirical threshold measurements to demonstrate that the models capture individual anatomical variability.

METHODS

Based on structural MRI data, we created models of the electric field (E-field) induced by right unilateral (RUL) electroconvulsive therapy (ECT) in four rhesus macaques. Individual motor threshold (MT) was measured with transcranial electric stimulation (TES) administered through the RUL electrodes in the same subjects.

RESULTS

The interindividual anatomical differences resulted in 57% variation in median E-field strength in the brain at fixed stimulus current amplitude. Individualization of the stimulus current by MT reduced the E-field variation in the target motor area by 27%. There was significant correlation between the measured MT and the ratio of simulated electrode current and E-field strength (r(2) = 0.95, p = 0.026). Exploratory analysis revealed significant correlations of this ratio with anatomical parameters including of the superior electrode-to-cortex distance, vertex-to-cortex distance, and brain volume (r(2) > 0.96, p < 0.02). The neural activation threshold was estimated to be 0.45 ±0.07 V/cm for 0.2-ms stimulus pulse width.

CONCLUSION

These results suggest that our individual-specific NHP E-field models appropriately capture individual anatomical variability relevant to the dosing of TES/ECT. These findings are exploratory due to the small number of subjects.

SIGNIFICANCE

This study can contribute insight in NHP studies of ECT and other brain stimulation interventions, help link the results to clinical studies, and ultimately lead to more rational brain stimulation dosing paradigms.

Effect of anatomical variability on electric field characteristics of electroconvulsive therapy and magnetic seizure therapy: a parametric modeling study

Electroconvulsive therapy (ECT) and magnetic seizure therapy (MST) are conventionally applied with a fixed stimulus current amplitude, which may result in differences in the neural stimulation strength and focality across patients due to interindividual anatomical variability. The objective of this study is to quantify the effect of head anatomical variability associated with age, sex, and individual differences on the induced electric field characteristics in ECT and MST. Six stimulation modalities were modeled including bilateral and right unilateral ECT, focal electrically administered seizure therapy (FEAST), and MST with circular, cap, and double-cone coils. The electric field was computed using the finite element method in a parameterized spherical head model representing the variability in the general population. Head tissue layer thicknesses and conductivities were varied to examine the impact of interindividual anatomical differences on the stimulation strength, depth, and focality. Skull conductivity most strongly affects the ECT electric field, whereas the MST electric field is independent of tissue conductivity variation in this model but is markedly affected by differences in head diameter. Focal ECT electrode configurations such as FEAST is more sensitive to anatomical variability than that of less focal paradigms such as BL ECT. In MST, anatomical variability has stronger influence on the electric field of the cap and circular coils compared to the double-cone coil, possibly due to the more superficial field of the former. The variability of the ECT and MST electric fields due to anatomical differences should be considered in the interpretation of existing studies and in efforts to improve dosing approaches for better control of stimulation strength and focality across patients, such as individualization of the current amplitude. The conventional approach to individualizing dosage by titrating the number of pulses cannot compensate for differences in the spatial extent of stimulation that result from anatomical variability.

Neuromodulation for mood and memory: from the engineering bench to the patient bedside

Brain stimulation, in the form of electroconvulsive therapy (ECT), has long been a gold standard treatment for depression, but today, the field of neuromodulation is rapidly changing with the advent of newer and more precise tools to alter neuroplasticity and to treat brain-based disorders. Now there are new means to induce focal seizures, as with magnetic seizure therapy (MST), or modifications to ECT. There are also surgical approaches to target brain circuits via implanted stimulators placed in the brain or on cranial nerves. Finally, there are noninvasive subconvulsive approaches for the transcranial application of either electric or magnetic fields. Collectively, these tools have transformed the face of neurotherapeutics and informed our understanding of the brain basis of complex neurobehavioral conditions.

Controlling stimulation strength and focality in electroconvulsive therapy via current amplitude and electrode size and spacing: comparison with magnetic seizure therapy

OBJECTIVES

Understanding the relationship between the stimulus parameters of electroconvulsive therapy (ECT) and the electric field characteristics could guide studies on improving risk/benefit ratio. We aimed to determine the effect of current amplitude and electrode size and spacing on the ECT electric field characteristics, compare ECT focality with magnetic seizure therapy (MST), and evaluate stimulus individualization by current amplitude adjustment.

METHODS

Electroconvulsive therapy and double-cone-coil MST electric field was simulated in a 5-shell spherical human head model. A range of ECT electrode diameters (2-5 cm), spacing (1-25 cm), and current amplitudes (0-900 mA) was explored. The head model parameters were varied to examine the stimulus current adjustment required to compensate for interindividual anatomical differences.

RESULTS

By reducing the electrode size, spacing, and current, the ECT electric field can be more focal and superficial without increasing scalp current density. By appropriately adjusting the electrode configuration and current, the ECT electric field characteristics can be made to approximate those of MST within 15%. Most electric field characteristics in ECT are more sensitive to head anatomy variation than in MST, especially for close electrode spacing. Nevertheless, ECT current amplitude adjustment of less than 70% can compensate for interindividual anatomical variability.

CONCLUSIONS

The strength and focality of ECT can be varied over a wide range by adjusting the electrode size, spacing, and current. If desirable, ECT can be made as focal as MST while using simpler stimulation equipment. Current amplitude individualization can compensate for interindividual anatomical variability.

Comparable seizure characteristics in magnetic seizure therapy and electroconvulsive therapy for major depression

Electroconvulsive therapy (ECT) is highly effective for treatment-resistant depression (TRD); however, its use for less severe forms of depression is somewhat limited by a lack of control over current spreading to medial temporal lobe memory structures, resulting in various cognitive side effects. In contrast, magnetic seizure therapy (MST), which uses high frequency repetitive transcranial magnetic stimulation (rTMS) for local seizure induction, has been associated with reduced cognitive side effects. To assess whether different characteristics of seizures induced by both methods are responsible for the differences in neuropsychological side-effect profile, we studied seven TRD-patients undergoing both MST and ECT in an open-label, within subject, controlled crossover pilot study. Comparison parameters included seizure-related ictal characteristics, including motor activity, electromyogram (EMG), electroencephalogram (EEG), and postictal recovery and reorientation times.Our results showed no differences in motor activity or EMG and EEG characteristics, thus implicating similar electrophysiological processes in seizure induction with MST and ECT. In line with previous studies, we observed shorter postictal recovery and reorientation times following MST.The ictal characteristics of induced seizures were found similar with ECT and MST suggesting that the more focal seizure induction associated with MST may account for the more beneficial neuropsychological side effect profile of MST.

Applications of transcranial magnetic stimulation and magnetic seizure therapy in the study and treatment of disorders related to cerebral aging

Transcranial magnetic stimulation (TMS) can be used to probe cortical function and treat neuropsychiatric illnesses. TMS has demonstrated neuroplastic effects akin to long-term potentiation and long-term depression, and therapeutic applications are in development for post-stroke recovery, Alzheimer's disease, and depression in seniors. Here, we discuss two new directions of TMS research relevant to cerebral aging and cognition. First, we introduce a paradigm for enhancing cognitive reserve, based on our research in sleep deprivation. Second, we discuss the use of magnetic seizure therapy (MST) to spare cognitive functions relative to conventional electroconvulsive therapy, and as a means of providing a more potent antidepressant treatment when subconvulsive TMS has shown modest efficacy in seniors. Whether in the enhancement of cognition as a treatment goal, or in the reduction of amnesia as a side effect, these approaches to the use of TMS and MST merit further exploration regarding their clinical potential.

Stimulation strength and focality of electroconvulsive therapy with individualized current amplitude: a preclinical study

This study investigates the stimulation strength and focality of electroconvulsive therapy (ECT) with individualized current amplitude in a nonhuman primate (NHP) model. We generated an anatomically realistic finite element model of a NHP head incorporating tissue heterogeneity and white matter conductivity anisotropy based on structural magnetic resonance imaging (MRI) and diffusion tensor MRI data. The electric field spatial distributions of three conventional ECT electrode placements (bilateral, bifrontal, and right unilateral) and an experimental frontomedial electrode configuration were simulated. We calibrated the electric field maps relative to an empirical neural activation threshold and evaluated the stimulation strength and focality of the various ECT electrode configurations with individualized current amplitudes corresponding to the motor threshold and seizure threshold assessed in the anesthetized NHP. Understanding the stimulation strength and focality of various forms of ECT could provide insight into the mechanisms of therapeutic seizure induction, and could provide support for the clinical investigation of ECT with individualized current amplitude as an intervention with potentially improved risk/benefit ratio.

Disruption of component processes of spatial working memory by electroconvulsive shock but not magnetic seizure therapy

Self-ordered spatial working memory measures provide important information regarding underlying cognitive strategies, such as stereotypy. This strategy is based on repetitive sequential selection of a spatial pattern once a correct sequence has been identified. We previously reported that electroconvulsive shock (ECS) but not magnetic seizure therapy (MST) impaired performance on a spatial working memory task in a preclinical model. Here we tested the hypothesis that ECS disrupted stereotyped patterns in the selection of spatial stimuli. In a within-subject study design, we assessed the effects of ECS, MST, and sham on stereotypy and reaction time in a preclinical model. Stereotypy was assessed by the correlation of actual and predicted response patterns of spatial stimuli. Predicted patterns were based on performance during baseline sessions. ECS resulted in lower correlations between predicted and actual responses to spatial stimuli in two of the three subjects, and it also disrupted stereotypy. For one subject, there was change in the predictability of the spatial locus of responses between experimental conditions. For all three subjects, reaction time was significantly longer in ECS, relative to MST and sham. This is the first study to examine the effect of ECS, and to contrast the effects of ECS and MST, on spatial working memory component processes. Our preliminary findings show that ECS, but not MST decreased stereotypy and increased reaction time. This line of investigation may have significant implications in our understanding cognitive component processes of memory function and impairment.

[Brain stimulation procedures. Transcranial magnetic stimulation, magnetic seizure therapy and deep brain stimulation]

Brain stimulation methods are promising treatment options in severe treatment-resistant psychiatric disorders. A safe and noninvasive method is transcranial magnetic stimulation, but the clinical application is not clear. Magnetic seizure therapy is a further development of transcranial magnetic stimulation, by which generalized seizures are induced under anaesthesia. Previous results with regard to the antidepressant effects and the fewer cognitive side effects were significant. Deep brain stimulation is an invasive procedure in which electrodes are stereotactically implanted in special brain areas. The effects in severe therapy-resistant obsessive-compulsive disorders and depressions are promising. However, the evaluation of ethical issues remains an important task.

Somatic treatments for mood disorders

Somatic treatments for mood disorders represent a class of interventions available either as a stand-alone option, or in combination with psychopharmacology and/or psychotherapy. Here, we review the currently available techniques, including those already in clinical use and those still under research. Techniques are grouped into the following categories: (1) seizure therapies, including electroconvulsive therapy and magnetic seizure therapy, (2) noninvasive techniques, including repetitive transcranial magnetic stimulation, transcranial direct current stimulation, and cranial electric stimulation, (3) surgical approaches, including vagus nerve stimulation, epidural electrical stimulation, and deep brain stimulation, and (4) technologies on the horizon. Additionally, we discuss novel approaches to the optimization of each treatment, and new techniques that are under active investigation.

The emerging use of brain stimulation treatments for psychiatric disorders

OBJECTIVE

The aim of this study was to review the current state of development and application of a wide range of brain stimulation approaches in the treatment of psychiatric disorders.

METHOD

The approaches reviewed include forms of minimally invasive magnetic and electrical stimulation, seizure induction, implanted devices and several highly novel approaches in early development.

RESULTS

An extensive range of brain stimulation approaches are now being widely used in the treatment of patients with psychiatric disorders, or actively investigated for this use. Both vagal nerve stimulation (VNS) and repetitive transcranial magnetic stimulation (rTMS) have been introduced into clinical practice in some countries. A small body of research suggests that VNS has some potentially long-lasting antidepressant effects in a minority of patients treated. rTMS has now been extensively investigated for over 15 years, with a large body of research now supporting its antidepressant effects. Further rTMS research needs to focus on defining the most appropriate stimulation methods and exploring its longer term use in maintenance protocols. Very early data suggest that magnetic seizure therapy (MST) has promise in the treatment of patients referred for electroconvulsive therapy: MST appears to have fewer side effects and may have similar efficacy. A number of other approaches including surgical and alternative forms of electrical stimulation appear to alter brain activity in a promising manner, but are in need of evaluation in more substantive patient samples.

CONCLUSIONS

It appears likely that the range of psychiatric treatments available for patients will grow over the coming years to progressively include a number of novel brain stimulation techniques.

The use of ECT and MST in treating depression

Electroconvulsive therapy (ECT) has been used clinically since 1938. Its most common use is in the treatment of depression: first line treatment where rapid recovery is a priority, but more frequently as an effective treatment for patients who do not respond to pharmacological and psychological approaches. Whilst it is widely hailed as an effective treatment, concerns about its effect on cognition remain. The development of magnetic seizure therapy (MST) over the past decade has attempted to devise a therapy with comparable efficacy to ECT, but without the associated cognitive side effects. The rationale for this is that MST uses magnetic fields to induce seizures in the cortex, without electrical stimulation of brain structures involved with memory. MST has been used successfully in the treatment of depression, yet there is a dearth of literature in comparison with ECT. We present a systematic review of the literature on ECT (from 2009-2011) and MST (from 2001-2011).

A systematic review of the neurocognitive effects of magnetic seizure therapy

Magnetic seizure therapy (MST) is a novel neurotherapeutic intervention in development for the treatment of major affective disorders. Like other neurotherapeutic strategies such as electroconvulsive therapy (ECT) or transcranial magnetic stimulation (TMS), a primary interest will be to monitor the associated neurocognitive effects. Thus, the purpose of this systematic review was to synthesize the available data on the neurocognitive effects of MST. The authors performed two independent literature searches with the following terms terms: MST, magnetic, magnetic seizure therapy, depression, neurocognition, cognitive, preclinical. We included in this review a total of eleven articles that mentioned MST and neurocognition in the abstract. The articles were divided into three methodological domains that included virtual computer simulations, preclinical studies, and clinical investigations. Collectively, the available evidence suggests MST has little to no adverse cognitive effects. Specifically, virtual computer simulations found the magnetic field was localized to grey matter, and preclinical studies found no neurocortical or neurocognitive sequelae. Clinical investigations found MST to be associated with rapid reorientation and intact anterograde and retrograde memory. Future investigations using translational methods are warranted to confirm these findings and to further determine the effects of MST on neurocognitive functions.

Neuropsychological safety of nucleus accumbens deep brain stimulation for major depression: effects of 12-month stimulation

OBJECTIVES

Deep brain stimulation (DBS) to the nucleus accumbens (NAcc-DBS) has antidepressant effects in patients suffering from treatment-resistant depression (TRD). However, limited information exists regarding the impact of NAcc-DBS on cognitive functioning. The aim of this study was to examine whether NAcc-DBS in patients with TRD has any cognitive effects.

METHODS

A comprehensive neuropsychological battery was administered to 10 patients with TRD before onset of bilateral NAcc-DBS and after 1 year of DBS stimulation. Neuropsychological testing covered the domains of attention, learning and memory, executive functions, visual perception, and language. Performance was analyzed at baseline and after 1 year of continuous DBS.

RESULTS

No evidence was found for cognitive decline following NAcc-DBS comparing test results after 1 year of NAcc-DBS with baseline. However, significantly improved cognitive performance on tests of attention, learning and memory, executive functions and visual perception was found. In addition, there was a general trend towards cognitive enhancement from below average to average performance. These procognitive effects were independent of the antidepressant effects of NAcc-DBS or changes in NAcc-DBS parameters.

CONCLUSIONS

These results not only support cognitive safety of NAcc-DBS but also stress its beneficial role in augmenting cognitive performance in patients with TRD.

Antidepressant effects, of magnetic seizure therapy and electroconvulsive therapy, in treatment-resistant depression

Major depression is a common mental health problem and associated with significant morbidity and mortality, including impaired social and physical functioning and increased risk for suicide. Electroconvulsive therapy (ECT) is highly efficacious in treatment-resistant depressive disorders, but cognitive side effects are frequently associated with the treatment. Magnetic seizure therapy (MST) is a form of convulsive therapy, using magnetic fields in order to induce therapeutic seizures. First studies suggested that cognitive side effects of MST, including postictal recovery time, are more benign than those resulting from ECT treatment. In this open-label study we tested the hypothesis that MST is associated with clinically significant antidepressant effects in treatment-resistant depression (TRD) as an add-on therapy to a controlled pharmacotherapy. Twenty patients suffering from TRD were randomly assigned to receive either MST or ECT starting from July 2006 until November 2008. Primary outcome measure was antidepressant response assessed by Montgomery Åsberg Depression Scale. Secondary outcome measures included Hamilton Depression Rating Scale, Hamilton Anxiety Scale, Beck Depression Inventory and 90-Item Symptom Checklist. Antidepressant response (improvement of 50% in MADRS ratings) was statistically significant and of similar size in both treatment groups. Cognitive side effects were observed in neither group. Characteristics in MST- and ECT-induced seizures were comparable, especially regarding ictal activity and postictal suppression. Thus, MST may be a potential alternative to ECT if efficacy and safety are validated in larger clinical trials.

Electric field strength and focality in electroconvulsive therapy and magnetic seizure therapy: a finite element simulation study

We present the first computational study comparing the electric field induced by various electroconvulsive therapy (ECT) and magnetic seizure therapy (MST) paradigms. Four ECT electrode configurations (bilateral, bifrontal, right unilateral, and focal electrically administered seizure therapy) and three MST coil configurations (circular, cap, and double cone) were modeled. The model incorporated a modality-specific neural activation threshold. ECT (0.3 ms pulse width) and MST induced the maximum electric field of 2.1-2.5 V cm⁻¹ and 1.1-2.2 V cm⁻¹ in the brain, corresponding to 6.2-7.2 times and 1.2-2.3 times the neural activation threshold, respectively. The MST electric field is more confined to the superficial cortex compared to ECT. The brain volume stimulated was much larger with ECT (up to 100%) than with MST (up to 8.2%). MST with the double-cone coil was the most focal, and bilateral ECT was the least focal. Our results suggest a possible biophysical explanation of the reduced side effects of MST compared to ECT. Our results also indicate that the conventional ECT pulse amplitude (800-900 mA) is much higher than necessary for seizure induction. Reducing the ECT pulse amplitude should be explored as a potential means of diminishing side effects.

Unaltered neuronal and glial counts in animal models of magnetic seizure therapy and electroconvulsive therapy

Anatomical evidence of brain damage from electroconvulsive therapy (ECT) is lacking; but there are no modern stereological studies in primates documenting its safety. Magnetic seizure therapy (MST) is under development as a less invasive form of convulsive therapy, and there is only one prior report on its anatomical effects. We discerned no histological lesions in the brains of higher mammals subjected to electroconvulsive shock (ECS) or MST, under conditions that model closely those used in humans. We sought to extend these findings by determining whether these interventions affected the number of neurons or glia in the frontal cortex or hippocampus. Twenty-four animals received 6 weeks of ECS, MST, or anesthesia alone, 4 days per week. After perfusion fixation, numbers of neurons and glia in frontal cortex and hippocampus were determined by unbiased stereological methods. We found no effect of either intervention on volumes or total number or numerical density of neurons or glia in hippocampus, frontal cortex, or subregions of these structures. Induction of seizures in a rigorous model of human ECT and MST therapy does not cause a change in the number of neurons or glia in potentially vulnerable regions of brain. This study, while limited to young, healthy, adult subjects, provides further evidence that ECT and MST, when appropriately applied, do not cause structural damage to the brain.

Differential heart rate response to magnetic seizure therapy (MST) relative to electroconvulsive therapy: a nonhuman primate model

Electroconvulsive therapy (ECT) is an effective treatment for severe depression; however, the induced therapeutic seizure acts on the autonomic nervous system and results in significant cardiac effects. This is an important consideration particularly in the elderly. Magnetic seizure therapy (MST) is in development as a less invasive alternative, but its effects on cardiac function have not been studied. We sought to model those effects in nonhuman primates to inform the development of safer neurostimulation interventions. Twenty four rhesus monkeys were randomly assigned to receive 6 weeks of daily treatment with electroconvulsive stimulation (ECS), magnetic seizure therapy (MST) or anesthesia-alone sham. Digitally acquired ECG and an automated R-wave and inter-R interval (IRI) sampling were used to measure intervention effects on heart rate (HR). Significant differences between experimental conditions were found in the HR as evidenced by changes in the immediate post-stimulus, ictal and postictal epochs. Immediate post-stimulus bradycardia was seen with ECS but not with MST. ECS induced significantly more tachycardia than MST or sham in both the ictal and postictal periods. MST resulted in a small, but statistically significant increase in HR during the postictal period relative to baseline. HR was found to increase by 25% and 8% in the ECS and MST conditions, respectively. MST resulted in significantly less marked sympathetic and parasympathetic response than did ECS. This differential physiological response is consistent with MST having a more superficial cortical site of action with less impact on deeper brain structures implicated in cardiac control relative to ECT. The clinical relevance of the topographical seizure spread of MST and its associated effects on the autonomic nervous system remain to be determined in human clinical trials.

Neurophysiological characterization of high-dose magnetic seizure therapy: comparisons with electroconvulsive shock and cognitive outcomes

Magnetic seizure therapy (MST) is under development as a means of improving cognitive outcomes with convulsive therapy through achieving better control over therapeutic seizure induction than is possible with conventional electroconvulsive therapy. In this investigation, we present the first neurophysiological characterization of high-dose MST (HD-MST, 6x seizure threshold) to see if a higher dose that is often used in human trials retains differential expression relative to electroconvulsive shock (ECS) and to explore the relationship between seizure expression and cognitive outcomes. To this end, rhesus monkeys received 4 weeks of daily treatment with ECS, HD-MST, and anesthesia-alone sham in counterbalanced order, with an interposed recovery period. Two channels of electroencephalogram were recorded during and immediately after the ictal period. Electroencephalogram power within delta, theta, alpha, and beta frequency bands was calculated. Electroconvulsive shock showed significantly more ictal power in all frequency bands than HD-MST (P < 0.01). Electroencephalogram power during the postictal period was significantly different among conditions only for the delta band. Higher ictal expression with ECS was associated with slowed completion time for an orientation task given immediately after the treatments. Our results support earlier findings demonstrating that MST- and ECS-induced seizures elicit differential patterns of ictal expression, consistent with the relatively more superficial stimulation achieved via magnetic induction in comparison with conventional electroconvulsive therapy. These results demonstrate that MST, even at high dose, results in seizures that differ neurophysiologically from ECS. It further suggests that some of the differences in ictal expression may relate to the improved cognitive outcomes seen with MST.

Focal electrically administered seizure therapy: a novel form of ECT illustrates the roles of current directionality, polarity, and electrode configuration in seizure induction

Electroconvulsive therapy (ECT) is a mainstay in the treatment of severe, medication-resistant depression. The antidepressant efficacy and cognitive side effects of ECT are influenced by the position of the electrodes on the head and by the degree to which the electrical stimulus exceeds the threshold for seizure induction. However, surprisingly little is known about the effects of other key electrical parameters such as current directionality, polarity, and electrode configuration. Understanding these relationships may inform the optimization of therapeutic interventions to improve their risk/benefit ratio. To elucidate these relationships, we evaluated a novel form of ECT (focal electrically administered seizure therapy, FEAST) that combines unidirectional stimulation, control of polarity, and an asymmetrical electrode configuration, and contrasted it with conventional ECT in a nonhuman primate model. Rhesus monkeys had their seizure thresholds determined on separate days with ECT conditions that crossed the factors of current directionality (unidirectional or bidirectional), electrode configuration (standard bilateral or FEAST (small anterior and large posterior electrode)), and polarity (assignment of anode and cathode in unidirectional stimulation). Ictal expression and post-ictal suppression were quantified through scalp EEG. Findings were replicated and extended in a second experiment with the same subjects. Seizures were induced in each of the 75 trials, including 42 FEAST procedures. Seizure thresholds were lower with unidirectional than with bidirectional stimulation (p<0.0001), and lower in FEAST than in bilateral ECS (p=0.0294). Ictal power was greatest in posterior-anode unidirectional FEAST, and post-ictal suppression was strongest in anterior-anode FEAST (p=0.0008 and p=0.0024, respectively). EEG power was higher in the stimulated hemisphere in posterior-anode FEAST (p=0.0246), consistent with the anode being the site of strongest activation. These findings suggest that current directionality, polarity, and electrode configuration influence the efficiency of seizure induction with ECT. Unidirectional stimulation and novel electrode configurations such as FEAST are two approaches to lowering seizure threshold. Furthermore, the impact of FEAST on ictal and post-ictal expression appeared to be polarity dependent. Future studies may examine whether these differences in seizure threshold and expression have clinical significance for patients receiving ECT.

Translational development strategy for magnetic seizure therapy

Electroconvulsive therapy (ECT) has unparalleled antidepressant efficacy, but its cognitive side effects may be persistent. Research suggests that the side effects may be at least partially dissociable from the therapeutic effects of ECT, suggesting that distinct cortical networks may underlie them and introducing a role for focal seizure induction as a means of minimizing side effects. In magnetic seizure therapy (MST), magnetic fields avoid tissue impedance and induce electrical currents confined to superficial cortex, facilitating focal seizure induction. The translational development strategy for MST has included: (1) device development, (2) feasibility in animals and initial human trials, (3) testing in nonhuman primates on safety and mechanisms of action (with neuroanatomical, neurophysiological and cognitive endpoints), (4) safety testing in patients, (5) initial efficacy testing in patients, (6) dosage optimization, and (7) randomized comparison with ECT. These stages have been iterative, with results of early clinical testing prompting device enhancements that were, in turn, tested in nonhuman primates prior to human trials. Safety testing was aided by development of a nonhuman primate model of human ECT, and the validation of a cognitive battery for the monkey that is sensitive to the range of effects of ECT on human memory. Human testing has been facilitated by the development of an international consortium of centers addressing various aspects of technique and dose/response relationships. Challenges facing MST are common to other device-based therapies: characterizing dose/response relationships, optimizing efficacy, and developing efficient and reliable methods to induce lasting therapeutic change in the circuitry underlying depression.

Quick recovery of orientation after magnetic seizure therapy for major depressive disorder

BACKGROUND

Magnetic seizure therapy, in which seizures are elicited with a high-frequency magnetic field, is under development as a new treatment for major depressive disorder. Its use may be justified if it produces the antidepressant effects of electroconvulsive therapy (ECT), coupled with limited cognitive side-effects.

AIMS

To evaluate the usefulness of a new 100 Hz magnetic seizure therapy device.

METHOD

We induced seizures with 100 Hz magnetic transcranial stimulation in 11 patients with major depressive disorder during one session of a regular course of ECT. Recovery times after seizures induced by magnetic seizure therapy and ECT were compared.

RESULTS

Seizures could be elicited in 10 of the 11 patients. Stimulation over the vertex produced tonic-clonic activity on 9 out of 11 occasions. Stimulation over the prefrontal midpoint elicited seizures on 3 out of 7 occasions. The mean duration of magnetically induced seizures was 31.3 s, ranging from 10 to 86 s. All patients had an exceptionally quick recovery of orientation: mean of 7 min 12 s (s.d.=2 min 7 s, range 4 min 20 s to 9 min 41 s). The recovery times were on average 15 min 35 s shorter with magnetic seizure therapy than with ECT in the same patients (paired-samples t-test: P<0.0001). Patients reported feeling less confused after magnetic seizure therapy. Side-effects were confined to myoclonic movements, associated with the use of etomidate.

CONCLUSIONS

The new 100 Hz magnetic stimulator elicits seizures in the majority of patients when administered over the vertex. Magnetic seizure therapy was associated with shorter recovery times and less confusion following treatment. Subsequent work will be required to assess the safety and effectiveness of magnetic seizure therapy in the treatment of depression.

Differential neurophysiological effects of magnetic seizure therapy (MST) and electroconvulsive shock (ECS) in non-human primates

Magnetic seizure therapy (MST) is under development as a means of reducing the side effects of electroconvulsive therapy (ECT) through enhanced control over patterns of seizure induction and spread. We previously reported that chronic treatment with MST resulted in less impairment in cognitive function than electroconvulsive shock (ECS) in a non-human primate model of convulsive therapy. Here we present quantitative analyses of ictal expression and post-ictal suppression following ECS, MST, and anesthesia-alone sham in the same model to test whether differential neurophysiological characteristics of the seizures could be identified. Rhesus monkeys received 4 weeks of daily treatment with ECS, MST, and anesthesia-alone sham in a counterbalanced order separated by a recovery period. Both ECS and MST were given bilaterally at 2.5 x seizure threshold. Neurophysiological characteristics were derived from two scalp EEG electrode recording sites during and immediately following the ictal period, and were compared to sham treatment. EEG power within four frequencies (delta, theta, alpha and beta) was calculated. Our results support earlier findings from intracerebral electrode recordings demonstrating that MST- and ECS- induced seizures elicit differential patterns of EEG activation. Specifically, we found that ECS shows significantly more marked ictal expression, and more intense post-ictal suppression than MST in the theta, alpha, and beta frequency bands (Ps < .05). However, the ECS and MST were indistinguishable in the delta frequency band during both ictal and post-ictal periods. These results demonstrate that magnetic seizure induction can result in seizures that differ in some neurophysiological respects compared with ECS, but that these modalities share some aspects of seizure expression. The clinical significance of these similarities and differences awaits clinical correlation.

Differential effects of high-dose magnetic seizure therapy and electroconvulsive shock on cognitive function

BACKGROUND

Magnetic seizure therapy (MST) is under investigation as an alternative form of convulsive therapy that induces more focal seizures and spares cortical regions involved in memory. With a newly expanded version of the Columbia University Primate Cognitive Profile, we compared the cognitive effects of high-dose MST delivered at 100 Hz (6 x seizure threshold) with electroconvulsive shock (ECS) delivered at 2.5 x seizure threshold.

METHODS

Daily high-dose MST, ECS, and sham (anesthesia-only) were administered for 4 weeks each in a within-subject crossover design. Rhesus macaques (n = 3) were trained on five cognitive tasks assessing automatic memory, anterograde learning and memory, combined anterograde and retrograde simultaneous chaining, and spatial and serial working memory. Acutely after each intervention, monkeys were tested on the cognitive battery twice daily, separated by a 3-hour retention interval.

RESULTS

Subjects were slower to complete criterion tasks (p values < .0001) after ECS, compared with sham and high-dose MST. Moreover, time to task-completion after high-dose MST did not differ from sham. Of six measures of accuracy, treatment effects were found in four; in all of these, ECS but not MST fared worse than sham. On all accuracy and time to completion measurements, subjects performed as well after high-dose MST as subjects from a previous study on moderate-dose MST.

CONCLUSIONS

These findings provide evidence that high-dose MST results in benign acute cognitive side-effect profile relative to ECS and are in line with our previous studies.

Nonpharmacological, somatic treatments of depression: electroconvulsive therapy and novel brain stimulation modalities

Until recently, a review of nonpharmacological, somatic treatments of psychiatric disorders would have included only electroconvulsive therapy (ECT). This situation is now changing very substantially. Although ECT remains the only modality in widespread clinical use, several new techniques are under investigation. Their principal indication in the psychiatric context is the treatment of major depression, but other applications are also being studied. All the novel treatments involve brain stimulation, which is achieved by different technological methods. The treatment closest to the threshold of clinical acceptability is transcranial magnetic stimulation (TMS). Although TMS is safe and relatively easy to administer, its efficacy has still to be definitively established. Other modalities, at various stages of research development, include magnetic seizure therapy (MST), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). We briefly review the development and technical aspects of these treatments, their potential role in the treatment of major depression, adverse effects, and putative mechanism of action. As the only one of these treatment modalities that is in widespread clinical use, more extended consideration is given to ECT Although more than half a century has elapsed since ECT was first introduced, it remains the most effective treatment for major depression, with efficacy in patients refractory to antidepressant drugs and an acceptable safety profile. Although they hold considerable promise, the novel brain stimulation techniques reviewed here will be need to be further developed before they achieve clinical acceptability.

Recent developments and current controversies in depression

In this review of the last 5 years' developments in research into depression we focus on recent advances and current controversies. We cover epidemiology and basic science as well as the treatment of depression in adults in all its forms. Depression in , as well as in has been covered in recent Seminars in The Lancet. Depression in adulthood remains a very common and under-treated condition, resulting in a high degree of disability. Increasingly detailed knowledge about impairment of information processing in depression is being supplemented by quantitative studies of the brain processes underlying these impairments. Most patients improve with present treatments. The mechanisms of action of antidepressants are not fully understood; the hypothesis that reversing hippocampal cell loss in depression may be their active principle is a fascinating new development. Moral panic about the claim that antidepressant serotonin reuptake inhibitors cause patients to commit suicide and become addicted to their medication may have disconcerted the public and members of the medical profession. We will try to describe the considerable effort that has gone into collecting evidence to enlighten this debate.