Animal models of the mechanisms of action of repetitive transcranial magnetic stimulation (RTMS): comparisons with electroconvulsive shock (ECS)

Repetitive transcranial magnetic stimulation promotes neurological functional recovery in rats with traumatic brain injury by upregulating synaptic plasticity-related proteins

Studies have shown that repetitive transcranial magnetic stimulation (rTMS) can enhance synaptic plasticity and improve neurological dysfunction. However, the mechanism through which rTMS can improve moderate traumatic brain injury remains poorly understood. In this study, we established rat models of moderate traumatic brain injury using Feeney’s weight-dropping method and treated them using rTMS. To help determine the mechanism of action, we measured levels of several important brain activity-related proteins and their mRNA. On the injured side of the brain, we found that rTMS increased the protein levels and mRNA expression of brain-derived neurotrophic factor, tropomyosin receptor kinase B, N-methyl-D-aspartic acid receptor 1, and phosphorylated cAMP response element binding protein, which are closely associated with the occurrence of long-term potentiation. rTMS also partially reversed the loss of synaptophysin after injury and promoted the remodeling of synaptic ultrastructure. These findings suggest that upregulation of synaptic plasticity-related protein expression is the mechanism through which rTMS promotes neurological function recovery after moderate traumatic brain injury.

5 Hz of repetitive transcranial magnetic stimulation improves cognition and induces modifications in hippocampal neurogenesis in adult female Swiss Webster mice

Adult hippocampal neurogenesis is regulated by several stimuli to promote the creation of a reserve that may facilitate coping with environmental challenges. In this regard, repetitive transcranial magnetic stimulation (rTMS), a neuromodulation therapy, came to our attention because in clinical studies it reverts behavioral and cognitive alterations related to changes in brain plasticity. Some preclinical studies emphasize the need to understand the underlying mechanism of rTMS to induce behavioral modifications. In this study, we investigated the effects of rTMS on cognition, neurogenic-associated modifications, and neuronal activation in the hippocampus of female Swiss Webster mice. We applied 5 Hz of rTMS twice a day for 14 days. Three days later, mice were exposed to the behavioral battery. Then, brains were collected and immunostained for Ki67-positive cells, doublecortin-positive (DCX+)-cells, calbindin, c-Fos and FosB/Delta-FosB in the dentate gyrus. Also, we analyzed mossy fibers and CA3 with calbindin immunostaining. Mice exposed to rTMS exhibited cognitive improvement, an increased number of proliferative cells, DCX cells, DCX cells with complex dendrite morphology, c-Fos and immunoreactivity of FosB/Delta-FosB in the granular cell layer. The volume of the granular cell layer, mossy fibers and CA3 in rTMS mice also increased. Interestingly, cognitive improvement correlated with DCX cells with complex dendrite morphology. Also, those DCX cells and calbindin immunoreactivity correlated with c-Fos in the granular cell layer. Our results suggest that 5 Hz of rTMS applied twice a day modify cell proliferation, doublecortin cells, mossy fibers and enhance cognitive behavior in healthy female Swiss Webster mice.

Effect of rTMS on GABA and glutamate levels in treatment-resistant depression: An MR spectroscopy study

Alterations in levels of neurotransmitters γ-aminobutyric acid (GABA) and glutamate may underlie the mechanism by which repetitive transcranial magnetic stimulation (rTMS) has efficacy as a treatment for major depressive disorder (MDD). This study used proton magnetic resonance spectroscopy (H¹MRS) to investigate the effect of rTMS on levels of GABA and combined glutamate/glutamine measure (Glx). Treatment-resistant, currently depressed individuals participated in a naturalistic open-label study with rTMS treatment administered at 10 Hz and 120% of resting motor threshold to the left dorsolateral prefrontal cortex (DLPFC) for 20 sessions. H¹ MRS measures were collected at baseline and after four weeks of daily treatment. GABA and Glx were measured from both the left DLPFC and a control region (right motor cortex). Twenty-seven participants completed the study and were included in the analysis. Contrary to previous studies, no difference in GABA was observed following treatment. Glx levels were found to significantly increase in both the left DLPFC and right motor cortex voxels but this increase did not correlate with antidepressant response. Glx levels were found to increase following rTMS, not only underlying the site of stimulation but also at a distant control voxel suggesting a degree of non-specificity in response to therapy.

A comparison of 15 minute vs 30 minute repetitive transcranial magnetic stimulation sessions for treatment resistant depression - are longer treatment sessions more effective?

BACKGROUND

Repetitive Transcranial Magnetic Stimulation (rTMS) is a safe and effective treatment for treatment resistant depression (TRD). The number of patients able to be treated with rTMS is determined by the availability of the machine and staff. If treatment delivered in a shorter time were just as effective as longer treatments, then more patients could be treated with the same resources.

METHOD

This naturalistic study investigated 145 first-time patients treated with 15 minute (900 pulses) or 30 minute (1800 pulses) RLF rTMS for TRD 3 days/week for 6 weeks. Response and remission rates for the two groups were compared. We investigated whether longer right unilateral low (1Hz) frequency (RLF) repetitive transcranial magnetic stimulation (rTMS) treatment sessions are more effective than shorter sessions in achieving response and remission for treatment resistant depression (TRD).

RESULTS

The duration of rTMS treatment sessions had no effect on treatment outcomes over the course of 6 weeks. The group treated with 15 minute rTMS sessions showed a partial response rate of 28.2%, a response rate of 11.5% and remission rate of 21.8%, which did not differ significantly from patients receiving 30 minute sessions who had a partial response rate of 25.4%, response rate of 17.9% and remission rate of 22.4%.

LIMITATIONS

Participants were not randomized and the inclusion criteria were broad and reflected the nature of patients seen in routine practice.

CONCLUSIONS

Fifteen minute rTMS sessions 3 days/week for 6 weeks were as effective as 30 minute sessions, providing a pragmatic advantage for shorter treatments.

Neuromodulation Management of Chronic Neuropathic Pain in The Central Nervous system

Neuromodulation is becoming one of the clinical tools for treating chronic neuropathic pain by transmitting controlled physical energy to the pre-identified neural targets in the central nervous system. Its nature of drug-free, non-addictive and improved targeting have attracted increasing attention among neuroscience research and clinical practices. This article provides a brief overview of the neuropathic pain and pharmacological routines for treatment, summarizes both the invasive and non-invasive neuromodulation modalities for pain management, and highlights an emerging brain stimulation technology, transcranial focused ultrasound (tFUS) with a focus on ultrasound transducer devices and the achieved neuromodulation effects and applications on pain management. Practical considerations of spatial guidance for tFUS are discussed for clinical applications. The safety of transcranial ultrasound neuromodulation and its future prospectives on pain management are also discussed.

Whither TMS: A One-Trick Pony or the Beginning of a Neuroscientific Revolution?

Psychiatry has been at the forefront of advancing clinical transcranial magnetic stimulation (TMS) since the mid-1990s, shortly after the invention of modern TMS in 1985 by Barker. Clinical TMS for psychiatric applications is advancing rapidly, with novel methods and innovations for treating depression, as well as a new clinical indication in obsessive-compulsive disorder. This review summarizes the recent findings and peers into the near future of this fertile and rapidly changing field. It is possible that many, perhaps even most, psychiatrists will be incorporating some form of brain stimulation into their practice within the next decade. The author summarizes the reasons for this optimistic view.

Development of Focused Transcranial Magnetic Stimulation for Rodents by Copper-Array Shields

Transcranial magnetic stimulation (TMS) is one of the most widely used noninvasive brain stimulation method. It has been utilized for both treatment and diagnosis of many neural diseases, such as neuropathic pain and loss of function caused by stroke. Existing TMS tools cannot deliver focused electric field to targeted penetration depth even though many important neurological disorders are originated from there. A breakthrough is needed to achieve noninvasive, focused brain stimulation. We demonstrated using magnetic shield to achieve magnetic focusing without sacrificing significant amount of throughput. The shield is composed of multiple layers of copper ring arrays, which utilize induced current to generate counter magnetic fields. We experimentally set up a two-pole stimulator system to verify device simulation. A transient magnetic field probe was used for field measurements. The focusing effect highly depends on the geometric design of shield. A tight focal spot with a diameter of smaller than 5mm (plotted in Matlab contour map) can be achieved by using copper ring arrays. With properly designed array structures and rings locations, the combined original and induced counter fields can produce a tightly focused field distribution with enhanced field strength at a depth 7.5mm beyond the shield plane, which is sufficient to reach many deep and critical parts of a mouse brain.

The Neuroprotective Effects of Long-Term Repetitive Transcranial Magnetic Stimulation on the Cortical Spreading Depression-induced Damages in Rat's Brain

INTRODUCTION

Cortical Spreading Depression (CSD) is a propagating wave of neural and glial cell depolarization with important role in several clinical disorders. Repetitive Transcranial Magnetic Stimulation (rTMS) is a potential tool with preventive treatment effects in psychiatric and neuronal disorders. In this paper, we study the effects of rTMS on CSD by using behavioral and histological approaches in hippocampus and cortical regions.

METHODS

Twenty-four rats were divided into four groups. A group of control rats were kept in their home cage during the experiment. The CSD group received four CSD inductions during 4 weeks with 1 week intervals. The CSD-rTMS group were treated with rTMS stimulation (figure-eight coils, 20 Hz, 10 min/d) for 4 weeks. The fourth group, i.e. rTMS group received rTMS stimulation similar to the CSD-rTMS group without CSD induction.

RESULTS

Long-term rTMS application in treated groups significantly reduced production of dark neurons, increased the mean volume of normal neurons, and decreased the number of apoptotic neurons in cortical regions compared to the control group. The protective effects of long-term treatment by rTMS in the hippocampal regions were also studied. It was effective in some regions; however, rTMS effects on hippocampal regions were lower than cortical ones.

CONCLUSION

Based on the study results, rTMS has significant preventive and protective effects in CSD-induced damages in cortical and hippocampal regions of the rat's brain.

A Neurophysiological Perspective on a Preventive Treatment against Schizophrenia Using Transcranial Electric Stimulation of the Corticothalamic Pathway

Schizophrenia patients are waiting for a treatment free of detrimental effects. Psychotic disorders are devastating mental illnesses associated with dysfunctional brain networks. Ongoing brain network gamma frequency (30–80 Hz) oscillations, naturally implicated in integrative function, are excessively amplified during hallucinations, in at-risk mental states for psychosis and first-episode psychosis. So, gamma oscillations represent a bioelectrical marker for cerebral network disorders with prognostic and therapeutic potential. They accompany sensorimotor and cognitive deficits already present in prodromal schizophrenia. Abnormally amplified gamma oscillations are reproduced in the corticothalamic systems of healthy humans and rodents after a single systemic administration, at a psychotomimetic dose, of the glutamate N-methyl-d-aspartate receptor antagonist ketamine. These translational ketamine models of prodromal schizophrenia are thus promising to work out a preventive noninvasive treatment against first-episode psychosis and chronic schizophrenia. In the present essay, transcranial electric stimulation (TES) is considered an appropriate preventive therapeutic modality because it can influence cognitive performance and neural oscillations. Here, I highlight clinical and experimental findings showing that, together, the corticothalamic pathway, the thalamus, and the glutamatergic synaptic transmission form an etiopathophysiological backbone for schizophrenia and represent a potential therapeutic target for preventive TES of dysfunctional brain networks in at-risk mental state patients against psychotic disorders.

Immediate Effects of Repetitive Magnetic Stimulation on Single Cortical Pyramidal Neurons

Repetitive Transcranial Magnetic Stimulation (rTMS) has been successfully used as a non-invasive therapeutic intervention for several neurological disorders in the clinic as well as an investigative tool for basic neuroscience. rTMS has been shown to induce long-term changes in neuronal circuits in vivo. Such long-term effects of rTMS have been investigated using behavioral, imaging, electrophysiological, and molecular approaches, but there is limited understanding of the immediate effects of TMS on neurons. We investigated the immediate effects of high frequency (20 Hz) rTMS on the activity of cortical neurons in an effort to understand the underlying cellular mechanisms activated by rTMS. We used whole-cell patch-clamp recordings in acute rat brain slices and calcium imaging of cultured primary neurons to examine changes in neuronal activity and intracellular calcium respectively. Our results indicate that each TMS pulse caused an immediate and transient activation of voltage gated sodium channels (9.6 ± 1.8 nA at -45 mV, p value < 0.01) in neurons. Short 500 ms 20 Hz rTMS stimulation induced action potentials in a subpopulation of neurons, and significantly increased the steady state current of the neurons at near threshold voltages (at -45 mV: before TMS: I = 130 ± 17 pA, during TMS: I = 215 ± 23 pA, p value = 0.001). rTMS stimulation also led to a delayed increase in intracellular calcium (153.88 ± 61.94% increase from baseline). These results show that rTMS has an immediate and cumulative effect on neuronal activity and intracellular calcium levels, and suggest that rTMS may enhance neuronal responses when combined with an additional motor, sensory or cognitive stimulus. Thus, these results could be translated to optimize rTMS protocols for clinical as well as basic science applications.

Contribution of TMS and rTMS in the Understanding of the Pathophysiology and in the Treatment of Dystonia

Dystonias represent a heterogeneous group of movement disorders responsible for sustained muscle contraction, abnormal postures, and muscle twists. It can affect focal or segmental body parts or be generalized. Primary dystonia is the most common form of dystonia but it can also be secondary to metabolic or structural dysfunction, the consequence of a drug's side-effect or of genetic origin. The pathophysiology is still not elucidated. Based on lesion studies, dystonia has been regarded as a pure motor dysfunction of the basal ganglia loop. However, basal ganglia lesions do not consistently produce dystonia and lesions outside basal ganglia can lead to dystonia; mild sensory abnormalities have been reported in the dystonic limb and imaging studies have shown involvement of multiple other brain regions including the cerebellum and the cerebral motor, premotor and sensorimotor cortices. Transcranial magnetic stimulation (TMS) is a non-invasive technique of brain stimulation with a magnetic field applied over the cortex allowing investigation of cortical excitability. Hyperexcitability of contralateral motor cortex has been suggested to be the trigger of focal dystonia. High or low frequency repetitive TMS (rTMS) can induce excitatory or inhibitory lasting effects beyond the time of stimulation and protocols have been developed having either a positive or a negative effect on cortical excitability and associated with prevention of cell death, γ-aminobutyric acid (GABA) interneurons mediated inhibition and brain-derived neurotrophic factor modulation. rTMS studies as a therapeutic strategy of dystonia have been conducted to modulate the cerebral areas involved in the disease. Especially, when applied on the contralateral (pre)-motor cortex or supplementary motor area of brains of small cohorts of dystonic patients, rTMS has shown a beneficial transient clinical effect in association with restrained motor cortex excitability. TMS is currently a valuable tool to improve our understanding of the pathophysiology of dystonia but large controlled studies using sham stimulation are still necessary to delineate the place of rTMS in the therapeutic strategy of dystonia. In this review, we will focus successively on the use of TMS as a tool to better understand pathophysiology, and the use of rTMS as a therapeutic strategy.

Trigeminal Nerve Stimulation for Comorbid Posttraumatic Stress Disorder and Major Depressive Disorder

OBJECTIVES

External stimulation of the trigeminal nerve (eTNS) is an emerging neuromodulation therapy for epilepsy and depression. Preliminary studies suggest it has an excellent safety profile and is associated with significant improvements in seizures and mood. Neuroanatomical projections of the trigeminal system suggest eTNS may alter activity in structures regulating mood, anxiety, and sleep. In this proof-of-concept trial, the effects of eTNS were evaluated in adults with posttraumatic stress disorder (PTSD) and comorbid unipolar major depressive disorder (MDD) as an adjunct to pharmacotherapy for these commonly co-occurring conditions.

MATERIALS AND METHODS

Twelve adults with PTSD and MDD were studied in an eight-week open outpatient trial (age 52.8 [13.7 sd], 8F:4M). Stimulation was applied to the supraorbital and supratrochlear nerves for eight hours each night as an adjunct to pharmacotherapy. Changes in symptoms were monitored using the PTSD Patient Checklist (PCL), Hamilton Depression Rating Scale (HDRS-17), Quick Inventory of Depressive Symptomatology (QIDS-C), and the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q).

RESULTS

Over the eight weeks, eTNS treatment was associated with significant decreases in PCL (p = 0.003; median decrease of 15 points; effect size d 1.5), HDRS-17 (p < 0.001; 42% response rate, 25% remission; d 2.1), and QIDS-C scores (p < 0.001; d 1.8), as well as an improvement in quality of life (Q-LES-Q, p < 0.01). eTNS was well tolerated with few treatment emergent adverse events.

CONCLUSIONS

Significant improvements in PTSD and depression severity were achieved in the eight weeks of acute eTNS treatment. This novel approach to wearable brain stimulation may have use as an adjunct to pharmacotherapy in these disorders if efficacy and tolerability are confirmed with additional studies.

The impact of rTMS over the dorsolateral prefrontal cortex on cognitive processing

The purpose of the present study was to use event-related potentials (ERP) to clarify the effect of magnetic stimulation on cognitive processing. A figure eight-shaped flat repetitive transcranial magnetic stimulation (rTMS) coil was used to stimulate either the region over the left or the right dorsolateral prefrontal cortex, which is considered to be the origin of the P300 component. Stimulus frequencies were 1.00, 0.75 and 0.50 Hz rTMS. The strength of the magnetic stimulation was set at 80% of the motor threshold for each participant. The auditory oddball task was used to elicit P300s before and shortly after rTMS, and comprised a sequence of sounds containing standard (1 kHz pure tone, 80% of trials) and deviant (2 kHz pure tone, 20% of trials) stimuli. We found that a 1.00 Hz rTMS pulse train over the left dorsolateral prefrontal cortex increased P300 latencies by 8.50 ms at Fz, 12.85 ms at Cz, and 11.25 ms at Pz. In contrast, neither 0.75 and 0.50 Hz rTMS pulse trains over the left dorsolateral prefrontal cortex nor 1.00, 0.75 and 0.50 Hz rTMS pulse trains over the right dorsolateral prefrontal cortex altered P300 latencies. These results indicate that rTMS frequency affects cognitive processing. Thus, we suggest that the effects of rTMS vary according to the activity of excitatory and inhibitory neurons in the cerebral cortex.

Possible Mechanisms Underlying the Therapeutic Effects of Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is an effective method used to diagnose and treat many neurological disorders. Although repetitive TMS (rTMS) has been used to treat a variety of serious pathological conditions including stroke, depression, Parkinson’s disease, epilepsy, pain, and migraines, the pathophysiological mechanisms underlying the effects of long-term TMS remain unclear. In the present review, the effects of rTMS on neurotransmitters and synaptic plasticity are described, including the classic interpretations of TMS effects on synaptic plasticity via long-term potentiation and long-term depression. We also discuss the effects of rTMS on the genetic apparatus of neurons, glial cells, and the prevention of neuronal death. The neurotrophic effects of rTMS on dendritic growth and sprouting and neurotrophic factors are described, including change in brain-derived neurotrophic factor concentration under the influence of rTMS. Also, non-classical effects of TMS related to biophysical effects of magnetic fields are described, including the quantum effects, the magnetic spin effects, genetic magnetoreception, the macromolecular effects of TMS, and the electromagnetic theory of consciousness. Finally, we discuss possible interpretations of TMS effects according to dynamical systems theory. Evidence suggests that a rTMS-induced magnetic field should be considered a separate physical factor that can be impactful at the subatomic level and that rTMS is capable of significantly altering the reactivity of molecules (radicals). It is thought that these factors underlie the therapeutic benefits of therapy with TMS. Future research on these mechanisms will be instrumental to the development of more powerful and reliable TMS treatment protocols.

Possible Mechanisms Underlying the Therapeutic Effects of Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is an effective method used to diagnose and treat many neurological disorders. Although repetitive TMS (rTMS) has been used to treat a variety of serious pathological conditions including stroke, depression, Parkinson's disease, epilepsy, pain, and migraines, the pathophysiological mechanisms underlying the effects of long-term TMS remain unclear. In the present review, the effects of rTMS on neurotransmitters and synaptic plasticity are described, including the classic interpretations of TMS effects on synaptic plasticity via long-term potentiation and long-term depression. We also discuss the effects of rTMS on the genetic apparatus of neurons, glial cells, and the prevention of neuronal death. The neurotrophic effects of rTMS on dendritic growth and sprouting and neurotrophic factors are described, including change in brain-derived neurotrophic factor concentration under the influence of rTMS. Also, non-classical effects of TMS related to biophysical effects of magnetic fields are described, including the quantum effects, the magnetic spin effects, genetic magnetoreception, the macromolecular effects of TMS, and the electromagnetic theory of consciousness. Finally, we discuss possible interpretations of TMS effects according to dynamical systems theory. Evidence suggests that a rTMS-induced magnetic field should be considered a separate physical factor that can be impactful at the subatomic level and that rTMS is capable of significantly altering the reactivity of molecules (radicals). It is thought that these factors underlie the therapeutic benefits of therapy with TMS. Future research on these mechanisms will be instrumental to the development of more powerful and reliable TMS treatment protocols.

The relationship between brain oscillatory activity and therapeutic effectiveness of transcranial magnetic stimulation in the treatment of major depressive disorder

Major depressive disorder (MDD) is marked by disturbances in brain functional connectivity. This connectivity is modulated by rhythmic oscillations of brain electrical activity, which enable coordinated functions across brain regions. Oscillatory activity plays a central role in regulating thinking and memory, mood, cerebral blood flow, and neurotransmitter levels, and restoration of normal oscillatory patterns is associated with effective treatment of MDD. Repetitive transcranial magnetic stimulation (rTMS) is a robust treatment for MDD, but the mechanism of action (MOA) of its benefits for mood disorders remains incompletely understood. Benefits of rTMS have been tied to enhanced neuroplasticity in specific brain pathways. We summarize here the evidence that rTMS entrains and resets thalamocortical oscillators, normalizes regulation and facilitates reemergence of intrinsic cerebral rhythms, and through this mechanism restores normal brain function. This entrainment and resetting may be a critical step in engendering neuroplastic changes and the antidepressant effects of rTMS. It may be possible to modify the method of rTMS administration to enhance this MOA and achieve better antidepressant effectiveness. We propose that rTMS can be administered: (1) synchronized to a patient's individual alpha frequency (IAF), or synchronized rTMS (sTMS); (2) as a low magnetic field strength sinusoidal waveform; and, (3) broadly to multiple brain areas simultaneously. We present here the theory and evidence indicating that these modifications could enhance the therapeutic effectiveness of rTMS for the treatment of MDD.

NON-INVASIVE BRAIN STIMULATION IN CHILDREN: APPLICATIONS AND FUTURE DIRECTIONS

Transcranial magnetic stimulation (TMS) is a neurostimulation and neuromodulation technique that has provided over two decades of data in focal, non-invasive brain stimulation based on the principles of electromagnetic induction. Its minimal risk, excellent tolerability and increasingly sophisticated ability to interrogate neurophysiology and plasticity make it an enviable technology for use in pediatric research with future extension into therapeutic trials. While adult trials show promise in using TMS as a novel, non-invasive, non-pharmacologic diagnostic and therapeutic tool in a variety of nervous system disorders, its use in children is only just emerging. TMS represents an exciting advancement to better understand and improve outcomes from disorders of the developing brain.

Repetitive transcranial magnetic stimulation to maintain treatment response to electroconvulsive therapy in depression: a case series

Electroconvulsive therapy (ECT) is the most effective treatment for a refractory major depression in the context of both unipolar and bipolar affective disorders. However, the relapse rate within the first 6 months after a successful course of ECT to treat a depressive episode can be as high 50%. Evidence-based strategies to prevent relapse have partial efficacy and are associated with problematic adverse effects limiting their use as long-term treatments. Repetitive transcranial magnetic stimulation (rTMS) has demonstrated efficacy in treatment-resistant depression with a favorable adverse effect profile. Herein, we describe six patients, four with unipolar and two with bipolar depression, where rTMS was used to maintain response after a successful course of acute and continuation ECT. rTMS was administered once or twice weekly, at 120% of the resting motor threshold. Patients received sequential bilateral rTMS (low frequency right: 600 pulses, then high frequency left: 3000 pulses). The site of stimulation was 6 cm anterior and 1 cm lateral from the site of maximum stimulation of the abductor pollicis brevis muscle. Depressive symptoms were monitored with the quick inventory of depressive symptoms-self rated. Five of the six patients were able to maintain their response status from 6 to 13 months at the time of last observation. The use of rTMS may be an important relapse prevention strategy following an acute course of ECT. Controlled studies comparing rTMS to current evidence-based relapse prevention strategies are warranted.

Efficacy of transcranial magnetic stimulation targets for depression is related to intrinsic functional connectivity with the subgenual cingulate

BACKGROUND

Transcranial magnetic stimulation (TMS) to the left dorsolateral prefrontal cortex (DLPFC) is used clinically for the treatment of depression. However, the antidepressant mechanism remains unknown and its therapeutic efficacy remains limited. Recent data suggest that some left DLPFC targets are more effective than others; however, the reasons for this heterogeneity and how to capitalize on this information remain unclear.

METHODS

Intrinsic (resting state) functional magnetic resonance imaging data from 98 normal subjects were used to compute functional connectivity with various left DLPFC TMS targets employed in the literature. Differences in functional connectivity related to differences in previously reported clinical efficacy were identified. This information was translated into a connectivity-based targeting strategy to identify optimized left DLPFC TMS coordinates. Results in normal subjects were tested for reproducibility in an independent cohort of 13 patients with depression.

RESULTS

Differences in functional connectivity were related to previously reported differences in clinical efficacy across a distributed set of cortical and limbic regions. Dorsolateral prefrontal cortex TMS sites with better clinical efficacy were more negatively correlated (anticorrelated) with the subgenual cingulate. Optimum connectivity-based stimulation coordinates were identified in Brodmann area 46. Results were reproducible in patients with depression.

CONCLUSIONS

Reported antidepressant efficacy of different left DLPFC TMS sites is related to the anticorrelation of each site with the subgenual cingulate, potentially lending insight into the antidepressant mechanism of TMS and suggesting a role for intrinsically anticorrelated networks in depression. These results can be translated into a connectivity-based targeting strategy for focal brain stimulation that might be used to optimize clinical response.

A randomized trial comparing repetitive transcranial magnetic stimulation given 3 days/week and 5 days/week for the treatment of major depression: is efficacy related to the duration of treatment or the number of treatments?

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) has been shown to be an effective treatment for depression. However, there has been little research to determine optimal parameters for treatment.

METHOD

This study compared two rTMS treatment regimes for the treatment of major depression. Seventy-seven participants were randomized to either spaced or daily treatment. Spaced rTMS was given 3 days/week for 6 weeks (18 treatments in total) and daily rTMS was given 5 days/week for 4 weeks (20 treatments in total). All participants were assessed at baseline and after 4 weeks of treatment. Participants in the spaced treatment group were also assessed after 6 weeks of treatment. All participants were treated at 110% of the resting motor threshold with high-frequency rTMS (10 Hz) to the left dorsolateral prefrontal cortex (DLPFC) followed by low-frequency rTMS to the right DLPFC.

RESULTS

Participants in the daily treatment group showed more improvement by week 4 than those in the spaced treatment group; however, both groups had similar improvement by treatment completion. There was significant improvement in both groups in ratings of depression and anxiety, with no significant differences between groups.

CONCLUSIONS

Our study indicates that the efficacy of rTMS is related to the number of treatments given and that spacing the treatments neither improves nor reduces efficacy.

High-frequency rTMS treatment increases white matter FA in the left middle frontal gyrus in young patients with treatment-resistant depression

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for treatment-resistant depression (TRD), but its therapeutic mechanisms are unclear. White matter abnormalities are thought to cause network dysfunction underlying TRD. Diffusion tensor imaging (DTI) is an ideal tool for examining neural connections and the integrity of white matter. Few studies have used DTI to investigate the impact of rTMS on alterations of whiter matter in TRD.

METHOD

30 young treatment-resistant unipolar depression patients (19 males and 11 females) were enrolled in a double-blind, randomized high-frequency (15 Hz) rTMS treatment study. Seventeen patients were treated with real stimulation, and 13 were treated with sham stimulation. White-matter fractional anisotropy (FA) was evaluated using voxel-based analysis (VBA) of FA maps derived from DTI before and after treatment. Twenty-five age- and gender-matched subjects were examined as a control group.

RESULTS

In an exploratory VBA method, clusters of fifty voxels or greater that survived a family-wise error (FWE)-corrected threshold of p<0.05 were considered significant. The results revealed significantly reduced FA in the left middle frontal gyrus, with peak coordinates [-18 46 -14] in TRD patients. This reduced FA was significantly improved after active rTMS treatment, but not sham stimulation. FA increases were correlated with decreased depressive symptoms.

LIMITATIONS

This study requires replication and further clarification in a larger patient population, and optimization of stimulation locations and methods.

CONCLUSIONS

These results suggest that the efficacy of rTMS on TRD is related to increased white-matter FA in the left middle frontal gyrus.

Increase in cortical pyramidal cell excitability accompanies depression-like behavior in mice: a transcranial magnetic stimulation study

Clinical evidence suggests that cortical excitability is increased in depressives. We investigated its cellular basis in a mouse model of depression. In a modified version of forced swimming (FS), mice were initially forced to swim for 5 consecutive days and then were treated daily with repetitive transcranial magnetic stimulation (rTMS) or sham treatment for the following 4 weeks without swimming. On day 2 through day 5, the mice manifested depression-like behaviors. The next and last FS was performed 4 weeks later, which revealed a 4 week maintenance of depression-like behavior in the sham mice. In slices from the sham controls, excitability in cingulate cortex pyramidal cells was elevated in terms of membrane potential and frequencies of spikes evoked by current injection. Depolarized resting potential was shown to depend on suppression of large conductance calcium-activated potassium (BK) channels. This BK channel suppression was confirmed by measuring spike width, which depends on BK channels. Chronic rTMS treatment during the 4 week period significantly reduced the depression-like behavior. In slices obtained from the rTMS mice, normal excitability and BK channel activity were recovered. Expression of a scaffold protein Homer1a was reduced by the FS and reversed by rTMS in the cingulate cortex. Similar recovery in the same behavioral, electrophysiological, and biochemical features was observed after chronic imipramine treatment. The present study demonstrated that manifestation and disappearance of depression-like behavior are in parallel with increase and decrease in cortical neuronal excitability in mice and suggested that regulation of BK channels by Homer1a is involved in this parallelism.

Dopaminergic neurotransmission in the human brain: new lessons from perturbation and imaging

Dopamine plays an important role in several brain functions and is involved in the pathogenesis of several psychiatric and neurological disorders. Neuroimaging techniques such as positron emission tomography allow us to quantify dopaminergic activity in the living human brain. Combining these with brain stimulation techniques offers us the unique opportunity to tackle questions regarding region-specific neurochemical activity. Such studies may aid clinicians and scientists to disentangle neural circuitries within the human brain and thereby help them to understand the underlying mechanisms of a given function in relation to brain diseases. Furthermore, it may also aid the development of alternative treatment approaches for various neurological and psychiatric conditions.

Roles of glutamate signaling in preclinical and/or mechanistic models of depression

Accumulating evidence suggests that the glutamatergic system plays important roles in the pathophysiology and treatment of major depressive disorder (MDD). Abnormalities in the glutamatergic system are definitely observed in this disorder, and certain glutamatergic agents exhibit antidepressant effects in patients with MDD. In this review, we summarize the preclinical findings suggesting the involvement of glutamate signaling in the pathophysiology and treatment of MDD. Preclinical animal models for depression are often characterized by changes in molecules related to glutamatergic signaling. Some antidepressants exert their effects by affecting glutamatergic system components in animals. Animals with genetically modified glutamatergic function exhibit depression-like behaviors or anti-depressive behavior. In addition, several types of glutamatergic agents have shown antidepressant-like effects in preclinical models for depression. Many types of glutamate receptors (NMDA, AMPA, and metabotropic glutamate receptors) or transporters appear to be involved in the etiology of depression or in the mechanisms of action of antidepressants. These functional proteins related to glutamate signal transduction are potential targets for a new generation of antidepressants with fast-onset effects, such as the NMDA antagonist ketamine.

The effect of daily prefrontal repetitive transcranial magnetic stimulation over several weeks on resting motor threshold

BACKGROUND

The resting motor threshold (rMT) is an important factor in the selection of treatment intensity for patients receiving repetitive transcranial magnetic stimulation (rTMS). In many clinical studies to date, due to concerns about potential drift, the rMT has been routinely re-measured weekly or every fifth session.

OBJECTIVE

Our aim is to investigate whether ongoing treatment with rTMS affects the rMT, the degree of change, and whether frequent remeasurement is needed.

METHODS

Clinical data were drawn from 50 medication free patients receiving treatment for major depression with rTMS in a large U.S. NIH-sponsored multisite study. Four measurements of rMT were obtained including before and after the double blind phase, followed by weekly measurements during the open phase. Active treatment consisted of 75 four second trains of 10Hz stimulation applied over 37.5 minutes with the coil over the left DLPFC at 120% rMT.

RESULTS

For the group as a whole, there was no significant change in the rMT during a minimum of 2 weeks of treatment with prefrontal rTMS (p=0.911, one way ANOVA). The average within-subject coefficient of variation was 6.58%. On average the last rMT was 2.45% less than the baseline rMT (range 32.3% increase, 40.6% decrease).

CONCLUSION

Daily left prefrontal rTMS over several weeks as delivered in this trial does not cause systematic changes in rMT. While most subjects had <10% variance in rMT over time, 5 subjects had changes of approximately 20% from baseline, raising dosing and safety issues if undetected. We recommend that clinical trials of rTMS have periodic retesting of rMT, especially if the dose is at or near the edge of the TMS safety tables.

A new strategy for antidepressant prescription

From our research and literature search we propose an understanding of the mechanism of action of antidepressants treatments (ADTs) that should lead to increase efficacy and tolerance. We understand that ADTs promote synaptic plasticity and neurogenesis. This promotion is linked with stimulation of dopaminergic receptors. Previous evidence shows that all ADTs (chemical, electroconvulsive therapy, repetitive transcranial magnetic stimulation, sleep deprivation) increase at least one monoamine neurotransmitter serotonin (5-HT), noradrenaline (NA) or dopamine (DA); this article focuses on DA release or turn-over in the frontal cortex. DA increased dopaminergic activation promotes synaptic plasticity with an inverted U shape dose–response curve. Specific interaction between DA and glutamate is mediated by D1 receptor subtypes and Glutamate (NMDA) receptors with neurotrophic factors likely to play a modulatory role. With the understanding that all ADTs have a common, final, DA-ergic stimulation that promotes synaptic plasticity we can predict that (1) AD efficiency is related to the compound strength for inducing DA-ergic stimulation. (2) ADT efficiency presents a therapeutic window that coincides with the inverted U shape DA response curve. (3) ADT delay of action is related to a “synaptogenesis and neurogenesis delay of action.” (4) The minimum efficient dose can be found by starting at a low dosage and increasing up to the patient response. (5) An increased tolerance requires a concomitant prescription of a few ADTs, with different or opposite adverse effects, at a very low dose. (6) ADTs could improve all diseases with cognitive impairments and synaptic depression by increasing synaptic plasticity and neurogenesis.

Why do some promising brain-stimulation devices fail the next steps of clinical development?

Interest in techniques of noninvasive brain stimulation (NIBS) has been growing exponentially in the last decade. Recent studies have shown that some of these techniques induce significant neurophysiological and clinical effects. Although recent results are promising, there are several techniques that have been abandoned despite positive initial results. In this study, we performed a systematic review to identify NIBS methods with promising preliminary clinical results that were not fully developed and adopted into clinical practice, and discuss its clinical, research and device characteristics. We identified five devices (transmeatal cochlear laser stimulation, transcranial micropolarization, transcranial electrostimulation, cranial electric stimulation and stimulation with weak electromagnetic fields) and compared them with two established NIBS devices (transcranial magnetic stimulation and transcranial direct current stimulation) and with well-known drugs used in neuropsychiatry (pramipexole and escitalopram) in order to understand the reasons why they failed to reach clinical practice and further steps of research development. Finally, we also discuss novel NIBS devices that have recently showed promising results: brain ultrasound and transcranial high-frequency random noise stimulation. Our results show that some of the reasons for the failure of NIBS devices with promising clinical findings are the difficulty to disseminate results, lack of controlled studies, duration of research development, mixed results and lack of standardization.

Site-specific antidepressant effects of repeated subconvulsive electrical stimulation: potential role of brain-derived neurotrophic factor

BACKGROUND

Electroconvulsive therapy (ECT) is a very effective treatment for major depression. This method involves robust nonfocal stimulation of the brain and can normalize both neurochemical alterations and depressive behavior in animal models. We hypothesized that short stimulation sessions of specific reward-related brain sites might induce similar effects.

METHODS

In the present study we compared behavioral and neurochemical effects produced by ECT and by repeated stimulation of reward-related brain sites, in a widely used rat model for depressive behavior induced by chronic mild stress (CMS). Different groups of rats received 10 sessions of either electroconvulsive shocks or subconvulsive electrical stimulation (SCES) of specific brain sites with an implanted electrode. The SCES temporal parameters were similar to those used in transcranial magnetic stimulation studies in humans. A battery of behavioral tests and measurements of brain-derived neurotrophic factor (BDNF) levels were used to assess the effectiveness of these treatments relative to sham treatments.

RESULTS

Repeated SCES of either the nucleus accumbens (NAC) or the ventral but not the dorsal prelimbic cortex (PLC) reversed the main behavioral deficit and the reduction of BDNF levels in the hippocampus that were induced by CMS. The ECT was more effective because it also normalized a behavioral deficit associated with anxiety but produced a learning and memory impairment.

CONCLUSIONS

This study implicates the ventral PLC and the NAC in the pathophysiology of depressive behavior and suggests that local intermittent SCES can induce an antidepressant effect similar to that of ECT, without the cognitive impairment caused by the convulsive treatment.

Transcranial magnetic stimulation in the treatment of psychiatric disorders

Transcranial magnetic stimulation (TMS) is an emerging novel treatment modality for psychiatric disorders, particularly major depression. A device for delivery of TMS was approved by the US Food and Drug Administration for treatment of major depressive disorder in adults. TMS is being studied for a variety of psychiatric disorders, including obsessive-compulsive disorder, post-traumatic stress disorder, and auditory hallucinations in schizophrenia. In this article, we describe TMS and its neurobiologic basis, as well as the efficacy and safety data of TMS with regard to a range of psychiatric disorders.

State-dependent variability of neuronal responses to transcranial magnetic stimulation of the visual cortex

Electrical brain stimulation is a promising tool for both experimental and clinical applications. However, the effects of stimulation on neuronal activity are highly variable and poorly understood. To investigate the basis of this variability, we performed extracellular recordings in the visual cortex following application of transcranial magnetic stimulation (TMS). Our measurements of spiking and local field potential activity exhibit two types of response patterns which are characterized by the presence or absence of spontaneous discharge following stimulation. This variability can be partially explained by state-dependent effects, in which higher pre-TMS activity predicts larger post-TMS responses. These results reveal the possibility that variability in the neural response to TMS can be exploited to optimize the effects of stimulation. It is conceivable that this feature could be utilized in real time during the treatment of clinical disorders.

Transcranial magnetic stimulation of small animals: a modeling study of the influence of coil geometry, size and orientation

Several recent studies have investigated the mechanisms of repetitive transcranial magnetic stimulation (rTMS) using small animals. However, there is still limited knowledge about the distribution of the induced electric field, and its dependence on coil size, geometry and orientation. In this work we calculate the electric field induced in a realistically shaped homogeneous mouse model by commercially available coils in several different orientations. The results show that the secondary field, resulting from charge accumulation at the skin - air interface, drastically changes the magnitude, decay and focality of the primary field induced by the coil. Accurate knowledge about the distribution of the field is invaluable in designing experimental protocols and new coils for small animal stimulation.

Antidepressant-like effects of echo-planar magnetic resonance imaging in mice determined using the forced swimming test

Echo-planar magnetic resonance imaging (EP-MRI), which is novel variant of MRI, is thought to have antidepressant properties in humans and animal models. Using the forced swimming test (FST), we investigated which monoaminergic system in mice is affected by EP-MRI. The short- and long-term effects of EP-MRI on immobility time in the FST and motor activity within a locomotor activity cage were examined. Two groups of mice underwent 20 min of EP-MRI in an MR scanner (Siemens, 1.5 T Symphony) either 23.5 or 1 h before the start of the second session of the FST. In both groups, the immobility duration in the FST was reduced, similar to effective antidepressant drug treatments. Climbing behavior in the 1-h group and swimming behavior in the 23.5-h group increased significantly, similar to that seen after the administration of desipramine (a noradrenaline reuptake inhibitor) and sertraline (a selective serotonin reuptake inhibitor), respectively. The findings support the hypothesis that EP-MRI has an antidepressant-like effect. We suggest that the antidepressant-like effect begins in the early period with noradrenaline systems and is maintained in the late period with serotonin systems.

Determination of zeta-potential in rat organotypic hippocampal cultures

zeta-potentials of entities such as cells and synaptosomes have been determined, but zeta of brain tissue has never been measured. Electroosmotic flow, and the resulting transport of neuroactive substances, would result from naturally occurring and experimentally or clinically induced electric fields if zeta is significant. We have developed a simple method for determining zeta in tissue. An electric field applied across a rat organotypic hippocampal slice culture (OHSC) drives fluorescent molecules through the tissue by both electroosmotic flow and electrophoresis. Fluorescence microscopy is used to determine each molecule's velocity. Independently, capillary electrophoresis is used to measure the molecules' electrophoretic mobilities. The experiment yields zeta-potential and average tissue tortuosity. The zeta-potential of OHSCs is -22 +/- 2 mV, and the average tortuosity is 1.83 +/- 0.06. In a refined experiment, zeta-potential is measured in various subregions. The zeta-potentials of the CA1 stratum pyramidale, CA3 stratum pyramidal, and dentate gyrus are -25.1 +/- 1.6 mV, -20.3 +/- 1.7 mV, and -25.4 +/- 1.0 mV, respectively. Simple dimensional arguments show that electroosmotic flow is potentially as important as diffusion in molecular transport.

Brain stimulation in poststroke rehabilitation

Brain stimulation techniques provide a powerful means to modulate the function of specific neural structures, and show potential for future applications in the rehabilitation of stroke patients. Recent studies have started to translate to the bedside the body of data gathered over the last few years on mechanisms underlying brain plasticity and stroke recovery. Both noninvasive and invasive brain stimulation techniques, such as repetitive transcranial magnetic stimulation, transcranial direct current stimulation and direct cortical stimulation with epidural electrodes, have recently been tested in small studies with stroke patients. The results to date are very promising. Nonetheless, we are still at an early stage in the field and further evidence is needed to assess the clinical impact of this new approach. In this review, we provide readers with a basic introduction to the field, summarize preliminary studies and discuss future directions.

Noninvasive human brain stimulation

Noninvasive brain stimulation with transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) is valuable in research and has potential therapeutic applications in cognitive neuroscience, neurophysiology, psychiatry, and neurology. TMS allows neurostimulation and neuromodulation, while tDCS is a purely neuromodulatory application. TMS and tDCS allow diagnostic and interventional neurophysiology applications, and focal neuropharmacology delivery. However, the physics and basic mechanisms of action remain incompletely explored. Following an overview of the history and current applications of noninvasive brain stimulation, we review stimulation device design principles, the electromagnetic and physical foundations of the techniques, and the current knowledge about the electrophysiologic basis of the effects. Finally, we discuss potential biomedical and electrical engineering developments that could lead to more effective stimulation devices, better suited for the specific applications.

Positive predictors for antidepressive response to prefrontal repetitive transcranial magnetic stimulation (rTMS)

Repetitive transcranial magnetic stimulation (rTMS) is a brain stimulation technique which had recently been investigated as a putative antidepressant intervention. However, there is little agreement about clinically useful predictors of rTMS outcome. Therefore, the objective of the present study was to determine whether specific biographical, clinical, and psychopathological parameters are associated with the antidepressant response to rTMS in a large sample of 70 depressive patients. We performed a logistic regression analysis in 70 patients with major depressive disorder treated with rTMS of the left dorsolateral prefrontal cortex testing the predictive value of various domains of the depression syndrome as well as the variables episode duration, degree of treatment resistance, and CORE criteria. Response was defined as a 50% reduction of the initial Hamilton score (HAMD). After two weeks of treatment, 21% of the patients showed a response to rTMS. The binary logistic regression model correctly assigned 86.7% of the responders and 96.4% of the non-responders to their final response group. In the model, a high level of sleep disturbances was a significant predictor for treatment response to rTMS. Also, a low score of treatment resistance and a short duration of episode were positive predictors. These findings provide new evidence that especially pronounced sleep disturbances may be a significant clinical predictor of a response to rTMS. Prospective rTMS studies are necessary to validate the predictive value of the derived model.

Detailed 3D models of the induced electric field of transcranial magnetic stimulation coils

Previous models neglected contributions from current elements spanning the full geometric extent of wires in transcranial magnetic stimulation (TMS) coils. A detailed account of TMS coil wiring geometry is shown to provide significant improvements in the accuracy of electric field (E-field) models. Modeling E-field dependence based on the TMS coil's wire width, height, shape and number of turns clearly improved the fit of calculated-to-measured E-fields near the coil body. Detailed E-field models were accurate up to the surface of the coil body (within 0.5% of measured) where simple models were often inadequate (up to 32% different from measured).

Sex differences in antidepressant-like effect of chronic repetitive transcranial magnetic stimulation in rats

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neurophysiological technique. Pre-clinical and clinical studies supported that rTMS might have antidepressant effects. However, whether antidepressant effect of chronic rTMS is gender-dependent is still unknown. In this study, male and female Wistar rats received 10-day rTMS (4 trains of 15 Hz; 200 stimuli/day; 1.0 T) or control condition, and then were subjected to the forced-swim test (FST). We found that female rats consistently showed higher activity levels than males in FST and revealed the significant effects of gender and rTMS as well as the interaction of gender and rTMS. The result suggested the antidepressant-like effects of chronic rTMS on behavioral components in FST are gender-dependent. The gender discrepancy related to rTMS should not be neglected in antidepressant treatment of rTMS.

Electroconvulsive therapy and transcranial magnetic stimulation: can they be considered valid modalities in the treatment of pediatric mood disorders?

Depression in children and adolescents is a severe and debilitating disorder and can be life-endangering. Even when it is not life-endangering, however, it has a grave impact on the quality of life of youngsters and their families, and interferes with normal growth and development. In recent years, the field of child psychiatry has become more aware of the limited applicability of data from the adult literature to children and adolescents and the limited resources that child psychiatrists have in treating depression. This awareness substantiates the need to define the place of electroconvulsive therapy and transcranial magnetic stimulation in the treatment of pediatric depression.

Rapid-rate transcranial magnetic stimulation of animal auditory cortex impairs short-term but not long-term memory formation

Bilateral rapid-rate transcranial magnetic stimulation (rTMS) of gerbil auditory cortex with a miniature coil device was used to study short-term and long-term effects on discrimination learning of frequency-modulated tones. We found previously that directional discrimination of frequency modulation (rising vs. falling) relies on auditory cortex processing and that formation of its memory depends on local protein synthesis. Here we show that, during training over 5 days, certain rTMS regimes contingent on training had differential effects on the time course of learning. When rTMS was applied several times per day, i.e. four blocks of 5 min rTMS each followed 5 min later by a 3-min training block and 15-min intervals between these blocks (experiment A), animals reached a high discrimination performance more slowly over 5 days than did controls. When rTMS preceded only the first two of four training blocks (experiment B), or when prolonged rTMS (20 min) preceded only the first block, or when blocks of experiment A had longer intervals (experiments C and D), no significant day-to-day effects were found. However, in experiment A, and to some extent in experiment B, rTMS reduced the within-session discrimination performance. Nevertheless the animals learned, as demonstrated by a higher performance the next day. Thus, our results indicate that rTMS treatments accumulate over a day but not strongly over successive days. We suggest that rTMS of sensory cortex, as used in our study, affects short-term memory but not long-term memory formation.