Transcranial magnetic stimulation: studying motor neurophysiology of psychiatric disorders

Single-Subject TMS Pulse Visualization on MRI-Based Brain Model: A precise method for mapping TMS pulses on cortical surface

Highly accurate visualization of the points of transcranial magnetic stimulation (TMS) application on the brain cortical surface could provide anatomy-specific analysis of TMS effects. TMS is widely used to activate cortical areas with high spatial resolution, and neuronavigation enables site-specific TMS of particular gyrus sites. Precise control of TMS application points is crucial in determining the stimulation effects. Here, we propose a method that gives an opportunity to visualize and analyze the stimulated cortical sites by processing multi-parameter data.•This method uses MRI data to create a participant's brain model for visualization. The MRI data is segmented to obtain a raw 3D model, which is further optimized in 3D modeling software.•A Python script running in Blender uses the TMS coil's orientation data and participant's brain 3D model to define and mark the cortical sites affected by the particular TMS pulse.•The Python script can be easily customized to visualize TMS points task-specifically.

Neural Correlates of Self-Reported Knee Function in Individuals After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Anterior cruciate ligament (ACL) rupture is a common knee injury among athletes and physically active adults. Despite surgical reconstruction and extensive rehabilitation, reinjuries are common and disability levels are high, even years after therapy and return to activity. Prolonged knee dysfunction may result in part from unresolved neuromuscular deficits of the surrounding joint musculature in response to injury. Indeed, "upstream" neurological adaptations occurring after injury may explain these persistent functional deficits. Despite evidence for injury consequences extending beyond the joint to the nervous system, the link between neurophysiological impairments and patient-reported measures of knee function remains unclear.

HYPOTHESIS

Patterns of brain activation for knee control are related to measures of patient-reported knee function in individuals after ACL reconstruction (ACL-R).

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

In this multicenter, cross-sectional study, participants with unilateral ACL-R (n = 25; 10 men, 15 women) underwent task-based functional magnetic resonance imaging testing. Participants performed repeated cycles of open-chain knee flexion/extension. Neural activation patterns during the movement task were quantified using blood oxygen level-dependent (BOLD) signals. Regions of interest were generated using the Juelich Histological Brain Atlas. Pearson product-moment correlations were used to determine the relationship between mean BOLD signal within each brain region and self-reported knee function level, as measured by the International Knee Documentation Committee index. Partial correlations were also calculated after controlling for time from surgery and sex.

RESULTS

Patient-reported knee function was positively and moderately correlated with the ipsilateral secondary somatosensory cortex (r = 0.57, P = 0.005) and the ipsilateral supplementary motor area (r = 0.51, P = 0.01).

CONCLUSION

Increased ipsilateral secondary sensorimotor cortical activity is related to higher perceived knee function.

CLINICAL RELEVANCE

Central nervous system mechanisms for knee control are related to subjective levels of knee function after ACL-R. Increased neural activity may reflect central neuroplastic strategies to preserve knee functionality after traumatic injury.

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

BACKGROUND

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

METHODS

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

RESULTS

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

LIMITATIONS

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

CONCLUSIONS

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

Assessment of Cortical Plasticity in Schizophrenia by Transcranial Magnetic Stimulation

Neural plasticity refers to the capability of the brain to modify its structure and/or function and organization in response to a changing environment. Evidence shows that disruption of neuronal plasticity and altered functional connectivity between distinct brain networks contribute significantly to the pathophysiological mechanisms of schizophrenia. Transcranial magnetic stimulation has emerged as a noninvasive brain stimulation tool that can be utilized to investigate cortical excitability with the aim of probing neural plasticity mechanisms. In particular, in pathological disorders, such as schizophrenia, cortical dysfunction, such as an aberrant excitatory-inhibitory balance in cortical networks, altered cortical connectivity, and impairment of critical period timing are very important to be studied using different TMS paradigms. Studying such neurophysiological characteristics and plastic changes would help in elucidating different aspects of the pathophysiological mechanisms underlying schizophrenia. This review attempts to summarize the findings of available TMS studies with diagnostic and characterization aims, but not with therapeutic purposes, in schizophrenia. Findings provide further evidence of aberrant excitatory-inhibitory balance in cortical networks, mediated by neurotransmitter pathways such as the glutamate and GABA systems. Future studies with combining techniques, for instance, TMS with brain imaging or molecular genetic typing, would shed light on the characteristics and predictors of schizophrenia.

Speech Fluency Improvement in Developmental Stuttering Using Non-invasive Brain Stimulation: Insights From Available Evidence

Developmental stuttering (DS) is a disturbance of the normal rhythm of speech that may be interpreted as very debilitating in the most affected cases. Interventions for DS are historically based on the behavioral modifications of speech patterns (e.g., through speech therapy), which are useful to regain a better speech fluency. However, a great variability in intervention outcomes is normally observed, and no definitive evidence is currently available to resolve stuttering, especially in the case of its persistence in adulthood. In the last few decades, DS has been increasingly considered as a functional disturbance, affecting the correct programming of complex motor sequences such as speech. Compatibly, understanding of the neurophysiological bases of DS has dramatically improved, thanks to neuroimaging, and techniques able to interact with neural tissue functioning [e.g., non-invasive brain stimulation (NIBS)]. In this context, the dysfunctional activity of the cortico-basal-thalamo-cortical networks, as well as the defective patterns of connectivity, seems to play a key role, especially in sensorimotor networks. As a consequence, a direct action on the functionality of "defective" or "impaired" brain circuits may help people who stutter to manage dysfluencies in a better way. This may also "potentiate" available interventions, thus favoring more stable outcomes of speech fluency. Attempts aiming at modulating (and improving) brain functioning of people who stutter, realized by using NIBS, are quickly increasing. Here, we will review these recent advancements being applied to the treatment of DS. Insights will be useful not only to assess whether the speech fluency of people who stutter may be ameliorated by acting directly on brain functioning but also will provide further suggestions about the complex and dynamic pathophysiology of DS, where causal effects and "adaptive''/''maladaptive" compensation mechanisms may be strongly overlapped. In conclusion, this review focuses future research toward more specific, targeted, and effective interventions for DS, based on neuromodulation of brain functioning.

Examining and Modulating Neural Circuits in Psychiatric Disorders With Transcranial Magnetic Stimulation and Electroencephalography: Present Practices and Future Developments

Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation technique uniquely equipped to both examine and modulate neural systems and related cognitive and behavioral functions in humans. As an examination tool, TMS can be used in combination with EEG (TMS-EEG) to elucidate directly, objectively, and noninvasively the intrinsic properties of a specific cortical region, including excitation, inhibition, reactivity, and oscillatory activity, irrespective of the individual's conscious effort. Additionally, when applied in repetitive patterns, TMS has been shown to modulate brain networks in healthy individuals, as well as ameliorate symptoms in individuals with psychiatric disorders. The key role of TMS in assessing and modulating neural dysfunctions and associated clinical and cognitive deficits in psychiatric populations is therefore becoming increasingly evident. In this article, the authors review TMS-EEG studies in schizophrenia and mood disorders, as most TMS-EEG studies to date have focused on individuals with these disorders. The authors present the evidence on the efficacy of repetitive TMS (rTMS) and theta burst stimulation (TBS), when targeting specific cortical areas, in modulating neural circuits and ameliorating symptoms and abnormal behaviors in individuals with psychiatric disorders, especially when informed by resting-state and task-related neuroimaging measures. Examples of how the combination of TMS-EEG assessments and rTMS and TBS paradigms can be utilized to both characterize and modulate neural circuit alterations in individuals with psychiatric disorders are also provided. This approach, along with the evaluation of the behavioral effects of TMS-related neuromodulation, has the potential to lead to the development of more effective and personalized interventions for individuals with psychiatric disorders.

Brain functional connectivity in chronic tic disorders and Gilles de la Tourette syndrome

The pathophysiology of chronic tic disorder (cTD) and Gilles de la Tourette syndrome (GTS) is characterized by the dysfunction of both motor and non - motor cortico - striatal - thalamo - cortical (CSTC) circuitries, which leads to tic release and comorbids. A role of fronto - parietal network (FPN) connectivity breakdown has been postulated for tic pathogenesis, given that the FPN entertain connections with limbic, paralimbic, and CSTC networks. Our study was aimed at characterizing the FPN functional connectivity in cTD and GTS in order to assess the role of its deterioration in tic severity and the degree of comorbids. We recorded scalp EEG during resting state in patients with cTD and GTS. The eLORETA current source densities were analyzed, and the lagged phase synchronization (LPS) was calculated to estimate nonlinear functional connectivity between cortical areas. We found that the FPN functional connectivity in delta band was more detrimental in more severe GTS patients. Also, the sensorimotor functional connectivity in beta2 band was stronger in more severe cTD and GTS patients. FPN functional connectivity deterioration correlated with comorbids presence and severity in patients with GTS. Our data suggest that a FPN disconnection may contribute to the motoric symptomatology and comorbid severity in GTS, whereas sensorimotor disconnection may contribute to tic severity in cTD and GTS. Although preliminary, our study points out a differently disturbed brain connectivity between patients with cTD and GTS. This may serve as diagnostic marker and potentially interesting base to develop pharmacological and noninvasive neuromodulation trials aimed at reducing tic symptomatology.

The Territory of my Body: Testosterone Prevents Limb Cooling in the Rubber Hand Illusion

The Rubber Hand Illusion (RHI) is an experimental paradigm for assessing changes in body ownership. Recent findings in the field suggest that social emotions can influence such changes and that empathic motivation in particular appears to positively predict the malleability of body representations. Since the steroid hormone, testosterone, is well known to interrupt certain forms of empathic processing, in the current study we investigated whether 0.5 mg of testosterone affected ownership indices of the RHI. Forty-nine females participated in a double-blind, placebo-controlled experiment in which the RHI was induced. Compared to placebo, testosterone had no effects on the alteration of subjective ownership over the rubber limb or on subjective sense of proprioceptive drift. However, unlike the placebo group, testosterone-treated participants did not display an objective decline in the temperature of their own (hidden) hand following induction of the illusion. These findings suggest that testosterone strengthens implicit but not explicit bodily self-representations. We propose that effective maintenance of implicit body boundaries can be regarded, conceptually, as a primary defensive state facilitating integrity of the self.

Efficacy of non-invasive brain stimulation on the symptom dimensions of schizophrenia: A meta-analysis of randomized controlled trials

Background

Transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) have shown promise in the treatment of schizophrenia.

Objective

To quantify the efficacy of double-blind randomized controlled trials (RCT) of tDCS and rTMS for the positive and negative symptoms of schizophrenia and identify significant moderators relating to patient-related features and stimulation parameters.

Methods

Systemic review and meta-analyses of the relevant literature published until February 1st, 2017 to assess treatment efficacy and quantify the contribution of potential moderator variables.

Results

We identified 7 RCTs on tDCS (involving 105 participants) and 30 RCTs on rTMS (involving 768 participants). Compared to sham, tDCS improved all symptom dimensions but the effect reached significance for negative symptoms (Hedge’s g = −0.63, p = 0.02). Efficacy for positive but not negative symptoms was linearly associated with cumulative tDCS stimulation. Compared to sham, rTMS improved hallucinations (Hedge’s g = −0.51, p < 0.001) and negative symptoms (Hedge’s g = −0.49, p = 0.01) but was associated with modest, non-significant worsening of positive symptoms (Hedge’s g = 0.28, p = 0.13). Higher pulse frequency (>10 Hz), motor threshold intensity of 110%, left prefrontal cortical treatment site and trial duration over 3 weeks were associated with improvement in negative symptoms and worsening in positive symptoms (all p < 0.03).

Conclusions

The symptom dimensions in schizophrenia may respond differently to brain stimulation interventions in a way that may reflect the interaction between disease- and treatment-related mechanisms. Our findings underscore the need for further research into patient selection prior to treatment assignment and greater refinement of stimulation protocols.

The Persisted Effects of Low-Frequency Repetitive Transcranial Magnetic Stimulation to Augment Task-Specific Induced Hand Recovery Following Subacute Stroke: Extended Study

OBJECTIVE

To examine the long-term effects of the low-frequency repetitive transcranial magnetic stimulation (LFrTMS) combined with task-specific training on paretic hand function following subacute stroke.

METHODS

Sixteen participants were randomly selected and grouped into two: the experimental group (real LFrTMS) and the control group (sham LF-rTMS). All the 16 participants were then taken through a 1-hour taskspecific training of the paretic hand. The corticospinal excitability (motor evoke potential [MEP] amplitude) of the non-lesioned hemisphere, and the paretic hand performance (Wolf Motor Function Test total movement time [WMFT-TMT]) were evaluated at baseline, after the LF-rTMS, immediately after task-specific training, 1 and 2 weeks after the training.

RESULTS

Groups comparisons showed a significant difference in the MEP after LF-rTMS and after the training. Compared to the baseline, the MEP of the experimental group significantly decreased after LF-rTMS and after the training and that effect was maintained for 2 weeks. Group comparisons showed significant difference in WMFT-TMT after the training. Only in the experimental group, the WMFT-TMT of the can lifting item significantly reduced compared to the baseline and the effect was sustained for 2 weeks.

CONCLUSION

The results of this study established that the improvement in paretic hand after task-specific training was enhanced by LF-rTMS and it persisted for at least 2 weeks.

An update on medications and noninvasive brain stimulation to augment language rehabilitation in post-stroke aphasia

INTRODUCTION

Aphasia is among the most debilitating outcomes of stroke. Aphasia is a language disorder occurring in 10-30% of stroke survivors. Speech and Language Therapy (SLT) is the gold standard, mainstay treatment for aphasia, but gains from SLT may be incomplete. Pharmaceutical and noninvasive brain stimulation (NIBS) techniques may augment the effectiveness of SLT. Areas covered: Herein reviewed are studies of the safety and efficacy of these adjunctive interventions for aphasia, including randomized placebo-controlled and open-label trials, as well as case series from Pubmed, using search terms 'pharmacological,' 'tDCS' or 'TMS' combined with 'aphasia' and 'stroke.' Expert commentary: Relatively small studies have included participants with a range of aphasia types and severities, using inconsistent interventions and outcome measures. Results to-date have provided promising, but weak to moderate evidence that medications and/or NIBS can augment the effects of SLT for improving language outcomes. We end with recommendations for future approaches to studying these interventions, with multicenter, double-blind, randomized controlled trials.

Noninvasive Brain Stimulation and Personal Identity: Ethical Considerations

As noninvasive brain stimulation (NIBS) technology advances, these methods may become increasingly capable of influencing complex networks of mental functioning. We suggest that these might include cognitive and affective processes underlying personality and belief systems, which would raise important questions concerning personal identity and autonomy. We give particular attention to the relationship between personal identity and belief, emphasizing the importance of respecting users' personal values. We posit that research participants and patients should be encouraged to take an active approach to considering the personal implications of altering their own cognition, particularly in cases of neurocognitive "enhancement." We suggest that efforts to encourage careful consideration through the informed consent process would contribute usefully to studies and treatments that use NIBS.

Efficacy of intermittent Theta Burst Stimulation (iTBS) and 10-Hz high-frequency repetitive transcranial magnetic stimulation (rTMS) in treatment-resistant unipolar depression: study protocol for a randomised controlled trial

Background

The treatment of depression remains a challenge since at least 40% of patients do not respond to initial antidepressant therapy and 20% present chronic symptoms (more than 2 years despite standard treatment administered correctly). Repetitive transcranial magnetic stimulation (rTMS) is an effective adjuvant therapy but still not ideal. Intermittent Theta Burst Stimulation (iTBS), which has only been used recently in clinical practice, could have a faster and more intense effect compared to conventional protocols, including 10-Hz high-frequency rTMS (HF-rTMS). However, no controlled study has so far highlighted the superiority of iTBS in resistant unipolar depression.

Methods/design

This paper focuses on the design of a randomised, controlled, double-blind, single-centre study with two parallel arms, carried out in France, in an attempt to assess the efficacy of an iTBS protocol versus a standard HF- rTMS protocol. Sixty patients aged between 18 and 75 years of age will be enrolled. They must be diagnosed with major depressive disorder persisting despite treatment with two antidepressants at an effective dose over a period of 6 weeks during the current episode. The study will consist of two phases: a treatment phase comprising 20 sessions of rTMS to the left dorsolateral prefrontal cortex, localised via a neuronavigation system and a 6-month longitudinal follow-up. The primary endpoint will be the number of responders per group, defined by a decrease of at least 50% in the initial score on the Montgomery and Asberg Rating Scale (MADRS) at the end of rTMS sessions. The secondary endpoints will be: response rate 1 month after rTMS sessions; number of remissions defined by a MADRS score of <8 at the endpoint and 1 month after; the number of responses and remissions maintained over the next 6 months; quality of life; and the presence of predictive markers of the therapeutic response: clinical (dimensional scales), neuropsychological (evaluation of cognitive functions), motor (objective motor testing) and neurophysiological (cortical excitability measurements).

Discussion

The purpose of our study is to check the assumption of iTBS superiority in the management of unipolar depression and we will discuss its effect over time. In case of a significant increase in the number of therapeutic responses with a prolonged effect, the iTBS protocol could be considered a first-line protocol in resistant unipolar depression.

Trial registration

ClinicalTrials.gov, Identifier NCT02376491. Registered on 17 February 2015 at http://clinicaltrials.gov.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-016-1764-8) contains supplementary material, which is available to authorized users.

Cortical excitability changes over time in progressive multiple sclerosis

In 25 patients with progressive forms of multiple sclerosis (MS), motor cortex excitability was longitudinally studied over one year by means of transcranial magnetic stimulation (TMS). The following TMS parameters were considered: resting and active motor thresholds (MTs), input-output curve, short-interval intracortical inhibition (SICI), and intracortical facilitation. Clinical evaluation was based on the Expanded Disability Status Scale (EDSS). In the 16 patients not receiving disease-modifying drugs, the EDSS score worsened, resting MT increased, and SICI decreased. By contrast, no clinical for neurophysiological changes were found over time in the nine patients receiving immunomodulatory therapy. The natural course of progressive MS appears to be associated with a decline in cortical excitability of both pyramidal neurons and inhibitory circuits. This pilot study based on a small sample suggests that disease-modifying drugs may allow cortical excitability to remain stable, even in patients with progressive MS.

Noninvasive Brain Stimulation in Pediatric Attention-Deficit Hyperactivity Disorder (ADHD): A Review

Attention-deficit hyperactivity disorder (ADHD) is one of the most prevalent neurodevelopmental disorders in the pediatric population. The clinical management of ADHD is currently limited by a lack of reliable diagnostic biomarkers and inadequate therapy for a minority of patients who do not respond to standard pharmacotherapy. There is optimism that noninvasive brain stimulation may help to address these limitations. Transcranial magnetic stimulation and transcranial direct current stimulation are 2 methods of noninvasive brain stimulation that modulate cortical excitability and brain network activity. Transcranial magnetic stimulation can be used diagnostically to probe cortical neurophysiology, whereas daily use of repetitive transcranial magnetic stimulation or transcranial direct current stimulation can induce long-lasting and potentially therapeutic changes in targeted networks. In this review, we highlight research showing the potential diagnostic and therapeutic applications of transcranial magnetic stimulation and transcranial direct current stimulation in pediatric ADHD. We also discuss the safety and ethics of using these tools in the pediatric population.

Performance Characterization of an Actively Cooled Repetitive Transcranial Magnetic Stimulation Coil for the Rat

OBJECTIVES

This study characterizes and validates a recently developed dedicated circular rat coil for small animal repetitive Transcranial Magnetic Stimulation (rTMS).

MATERIALS AND METHODS

The electric (E) field distribution was calculated in a three-dimensional (3D) spherical rat head model and coil cooling performance was characterized. Motor threshold (MT) in rats (n = 12) was determined using two current directions, MT variability (n = 16) and laterality (n = 11) of the stimulation was assessed. Finally, 2-deoxy-2-((18) F)fluoro-D-glucose ([(18) F]-FDG) small animal Positron Emission Tomography (µPET) after sham and 1, 10, and 50 Hz rTMS stimulation (n = 9) with the new Cool-40 Rat Coil (MagVenture, Denmark) was performed.

RESULTS

The coil could produce high E-fields of maximum 220 V/m and more than 100 V/m at depths up to 5.3 mm in a ring-shaped distribution. No lateralization of stimulation was observed. Independent of the current direction, reproducible MT measurements were obtained at low percentages (27 ± 6%) of the maximum machine output (MO, MagPro X100 [MagVenture, Denmark]). At this intensity, rTMS with long pulse trains is feasible (1 Hz: continuous stimulation; 5 Hz: 1000 pulses; 10 Hz and 50 Hz: 272 pulses). When compared to sham, rTMS at different frequencies induced decreases in [(18) F]-FDG-uptake bilaterally mainly in dorsal cortical regions (visual, retrosplenial, and somatosensory cortices) and increases mainly in ventral regions (entorhinal cortex and amygdala).

CONCLUSION

The coil is suitable for rTMS in rats and achieves unprecedented high E-fields at high stimulation frequencies and long durations with however a rather unfocal rat brain stimulation. Reproducible MEPs as well as alterations in cerebral glucose metabolism following rTMS were demonstrated.

The effects of testosterone and insulin-like growth factor 1 on motor system form and function

In this perspective article, we review the effects of selected anabolic hormones on the motoric system and speculate on the role these hormones may have on influencing muscle and physical function via their impact on the nervous system. Both muscle strength and anabolic hormone levels decline around middle age into old age over a similar time period, and several animal and human studies indicate that exogenously increasing anabolic hormones (e.g., testosterone and insulin-like growth factor-1 (IGF-1)) in aged subjects is positively associated with improved muscle strength. While most studies in humans have focused on the effects of anabolic hormones on muscle growth, few have considered the impact these hormones have on the motoric system. However, data from animals demonstrate that administering either testosterone or IGF-1 to cells of the central and peripheral motor system can increase cell excitability, attenuate atrophic changes, and improve regenerative capacity of motor neurons. While these studies do not directly indicate that changes in anabolic hormones contribute to reduced human performance in the elderly (e.g., muscle weakness and physical limitations), they do suggest that additional research is warranted along these lines.

[Fundamentals and Clinical Applications of Transcranial Magnetic Stimulation in Neuropsychiatry]

Transcranial Magnetic Stimulation (TMS) is a non-invasive method for stimulation of brain that is based on the ability of a generated magnetic field to penetrate skull and brain meninges, inducing an electric current in the brain tissues that produces neuronal depolarization. TMS can be applied as single pulse of stimulation, pairs of stimuli separated by variable intervals to the same or different brain areas, or as trains of repetitive stimuli at various frequencies. Its mechanism of action is currently unknown. Repetitive TMS can modify the excitability of the cerebral cortex, and has been postulated as a diagnostic and therapeutic tool in the area of neuropsychiatry. The aim of this article is to review the knowledge of the TMS as regards its basic principles, pathophysiological mechanism, and its usefulness in clinical practice.

Cognitive enhancement

Cognitive enhancement refers to the improvement of cognitive ability in normal healthy individuals. In this article, we focus on the use of pharmaceutical agents and brain stimulation for cognitive enhancement, reviewing the most common methods of pharmacologic and electronic cognitive enhancement, and the mechanisms by which they are believed to work, the effectiveness of these methods and their prevalence. We note the many gaps in our knowledge of these matters, including open questions about the size, reliability and nature of the enhancing effects, and we conclude with recommendations for further research. WIREs Cogn Sci 2014, 5:95-103. doi: 10.1002/wcs.1250 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Utilizing repetitive transcranial magnetic stimulation to improve language function in stroke patients with chronic non-fluent aphasia

Transcranial magnetic stimulation (TMS) has been shown to significantly improve language function in patients with non-fluent aphasia(1). In this experiment, we demonstrate the administration of low-frequency repetitive TMS (rTMS) to an optimal stimulation site in the right hemisphere in patients with chronic non-fluent aphasia. A battery of standardized language measures is administered in order to assess baseline performance. Patients are subsequently randomized to either receive real rTMS or initial sham stimulation. Patients in the real stimulation undergo a site-finding phase, comprised of a series of six rTMS sessions administered over five days; stimulation is delivered to a different site in the right frontal lobe during each of these sessions. Each site-finding session consists of 600 pulses of 1 Hz rTMS, preceded and followed by a picture-naming task. By comparing the degree of transient change in naming ability elicited by stimulation of candidate sites, we are able to locate the area of optimal response for each individual patient. We then administer rTMS to this site during the treatment phase. During treatment, patients undergo a total of ten days of stimulation over the span of two weeks; each session is comprised of 20 min of 1 Hz rTMS delivered at 90% resting motor threshold. Stimulation is paired with an fMRI-naming task on the first and last days of treatment. After the treatment phase is complete, the language battery obtained at baseline is repeated two and six months following stimulation in order to identify rTMS-induced changes in performance. The fMRI-naming task is also repeated two and six months following treatment. Patients who are randomized to the sham arm of the study undergo sham site-finding, sham treatment, fMRI-naming studies, and repeat language testing two months after completing sham treatment. Sham patients then cross over into the real stimulation arm, completing real site-finding, real treatment, fMRI, and two- and six-month post-stimulation language testing.

Non-invasive brain stimulation: a new frontier in the treatment of neurogenic speech-language disorders

There is a growing body of evidence to support the use of non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) for the treatment of acquired speech and language disorders. The aim of the present paper is to review evidence to support the use of these procedures in the treatment of aphasia and dysarthria. Both TMS and tDCS are described in terms of their underlying principles and biophysics and their relative advantages and disadvantages for rehabilitation of acquired neurogenic communication disorders. Several studies have documented positive effects of inhibitory repetitive TMS (rTMS) to right Broca's area homologue on language recovery in non-fluent aphasia post-stroke. Improved language outcomes subsequent to high frequency rTMS applied to the lesioned hemisphere have also been documented. Similarly, therapeutic benefits have also been reported following tDCS, although the findings are less consistent than is the case with rTMS. Improved articulatory function and speech intelligibility has been noted in response to stimulation with excitatory rTMS in Parkinson's disease. It is suggested that the use of brain stimulation techniques in combination with more traditional therapies may represent the most innovative future approach to the treatment of acquired communication disorders.

Blood flow and oxygenation changes due to low-frequency repetitive transcranial magnetic stimulation of the cerebral cortex

Transcranial magnetic stimulation (TMS) modulates processing in the human brain and is therefore of interest as a treatment modality for neurologic conditions. During TMS administration, an electric current passing through a coil on the scalp creates a rapidly varying magnetic field that induces currents in the cerebral cortex. The effects of low-frequency (1 Hz), repetitive TMS (rTMS) on motor cortex cerebral blood flow (CBF) and tissue oxygenation in seven healthy adults, during/after 20 min stimulation, is reported. Noninvasive optical methods are employed: diffuse correlation spectroscopy (DCS) for blood flow and diffuse optical spectroscopy (DOS) for hemoglobin concentrations. A significant increase in median CBF (33%) on the side ipsilateral to stimulation was observed during rTMS and persisted after discontinuation. The measured hemodynamic parameter variations enabled computation of relative changes in cerebral metabolic rate of oxygen consumption during rTMS, which increased significantly (28%) in the stimulated hemisphere. By contrast, hemodynamic changes from baseline were not observed contralateral to rTMS administration (all parameters, p>0.29). In total, these findings provide new information about hemodynamic/metabolic responses to low-frequency rTMS and, importantly, demonstrate the feasibility of DCS/DOS for noninvasive monitoring of TMS-induced physiologic effects.

Transcranial magnetic stimulation in the assessment of motor cortex excitability and treatment of drug-resistant major depression

Major depression is one of the leading causes of disabling condition worldwide and its treatment is often challenging and unsatisfactory, since many patients become refractory to pharmacological therapies. Transcranial magnetic stimulation (TMS) is a noninvasive neurophysiological investigation mainly used to study the integrity of the primary motor cortex excitability and of the cortico-spinal tract. The development of paired-pulse and repetitive TMS (rTMS) paradigms has allowed investigators to explore the pathophysiology of depressive disorders and other neuropsychiatric diseases linked to brain excitability dysfunctions. Repetitive transcranial magnetic stimulation has also therapeutic and rehabilitative capabilities since it is able to induce changes in the excitability of inhibitory and excitatory neuronal networks that may persist in time. However, the therapeutic effects of rTMS on major depression have been demonstrated by analyzing only the improvement of neuropsychological performance. The aim of this study was to investigate cortical excitability changes on 12 chronically-medicated depressed patients (test group) after rTMS treatment and to correlate neurophysiological findings to neuropsychological outcomes. In detail, we assessed different parameters of cortical excitability before and after active rTMS in the test group, then compared to those of 10 age-matched depressed patients (control group) who underwent sham rTMS. In line with previous studies, at baseline both groups exhibited a significant interhemispheric difference of motor cortex excitability. This neurophysiological imbalance was then reduced in the patients treated with active rTMS, resulting also in a clinical benefit as demonstrated by the improvement in neuropsychological test scores. On the contrary, after sham rTMS, the interhemispheric difference was still evident in the control group. The reported clinical benefits in the test group might be related to the plastic remodeling of synaptic connection induced by rTMS treatment.

Benefit of multiple sessions of perilesional repetitive transcranial magnetic stimulation for an effective rehabilitation of visuospatial function

Noninvasive neurostimulation techniques have been used alone or in conjunction with rehabilitation therapy to treat the neurological sequelae of brain damage with rather variable therapeutic outcomes. One potential factor limiting a consistent success for such techniques may be the limited number of sessions carried out in patients, despite reports that their accrual may play a key role in alleviating neurological deficits long-term. In this study, we tested the effects of seventy consecutive sessions of perilesional high-frequency (10 Hz) repetitive transcranial magnetic stimulation (rTMS) in the treatment of chronic neglect deficits in a well-established feline model of visuospatial neglect. Under identical rTMS parameters and visuospatial testing regimes, half of the subjects improved in visuospatial orienting performance. The other half experienced either none or extremely moderate ameliorations in the neglected hemispace and displayed transient patterns of maladaptive visuospatial behavior. Detailed analyses suggest that lesion location and extent did not account for the behavioral differences observed between these two groups of animals. We conclude that multi-session perilesional rTMS regimes have the potential to induce functional ameliorations following focal chronic brain injury, and that behavioral performance prior to the onset of the rTMS treatment is the factor that best predicts positive outcomes for noninvasive neurostimulation treatments in visuospatial neglect.

Mechanisms of aphasia recovery after stroke and the role of noninvasive brain stimulation

One of the most frequent symptoms of unilateral stroke is aphasia, the impairment or loss of language functions. Over the past few years, behavioral and neuroimaging studies have shown that rehabilitation interventions can promote neuroplastic changes in aphasic patients that may be associated with the improvement of language functions. Following left hemisphere strokes, the functional reorganization of language in aphasic patients has been proposed to involve both intrahemispheric interactions between damaged left hemisphere and perilesional sites and transcallosal interhemispheric interactions between the lesioned left hemisphere language areas and homotopic regions in the right hemisphere. A growing body of evidence for such reorganization comes from studies using transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), two safe and noninvasive procedures that can be applied clinically to modulate cortical excitability during post-stroke language recovery. We discuss a hierarchical model for the plastic changes in language representation that occur in the setting of dominant hemisphere stroke and aphasia. We further argue that TMS and tDCS are potentially promising tools for enhancing functional recovery of language and for further elucidating mechanisms of plasticity in patients with aphasia.

Rethinking the thinking cap: ethics of neural enhancement using noninvasive brain stimulation

Although a growing body of evidence suggests that noninvasive brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct current stimulation have the capacity to enhance neural function in both brain-injured and neurally intact individuals, the implications of their potential use for cosmetic self-enhancement have not been fully explored. We review 3 areas in which noninvasive brain stimulation has the potential to enhance neurologic function: cognitive skills, mood, and social cognition. We then characterize the ethical problems that affect the practice of cosmetic neurology, including safety, character, justice, and autonomy, and discuss how these problems may apply to the use of noninvasive brain stimulation for self-enhancement.

Cortical motor neurophysiology of patients with schizophrenia: a study using transcranial magnetic stimulation

Trancranial magnetic stimulation (TMS) provides a non-invasive means for exploring physiological alterations of central motor control in a variety of neuropsychiatric diseases. The present study aimed to assess the neurophysiological profile of muscle evoked responses to a standard TMS procedure in 51 medicated patients with schizophrenia and 51 age- and sex-matched healthy subjects. Motor evoked potentials (MEPs) from the abductor pollicis brevis muscle were elicited by stimulation of the contralateral motor cortex with a circular coil. The hot spot was marked, and the resting motor threshold (RMTh), the stimulus intensity for maximum MEP (SI-max), the post-stimulus silent period of voluntary muscle activity, and MEP latency and amplitude were measured. The main findings were the significantly higher than normal values for RMTh and SI-max, which are both indices of neuronal excitability. In particular, patients who had ziprasidone in their therapeutic regimen demonstrated the highest SI-max for both hemispheres, and the highest RMTh for the left hemisphere, patients receiving olanzapine demonstrated the lowest RMTh for the left hemisphere, and those on quetiapine showed intermediate values. The silent period was longer in the patients than in the controls when a RMTh-related SI was used and did not differ between the two groups when a fixed SI was used. We concluded that the observed TMS changes could be interpreted as primary alterations of intracortical motor excitability followed by defects of cortical inhibition and should be attributed to schizophrenia, antipsychotic medication or the interaction between the two factors.

Increased cortical inhibition deficits in first-episode schizophrenia with comorbid cannabis abuse

RATIONALE/OBJECTIVES

There is a high prevalence of substance use disorder (SUD) in first-episode schizophrenia (SZ), but its contribution to the underlying SZ pathophysiology remains unclear. Several studies using transcranial magnetic stimulation (TMS) have observed abnormalities in human motor cortex (M1) excitability in SZ. Studies on cortical excitability comparing SZ patients with and without comorbid substance abuse are lacking.

METHODS

A total of 29 first-episode SZ patients participated in this study; 12 had a history of comorbid cannabis abuse (SZ-SUD) and 17 did not (SZ-NSUD). We applied TMS to right and left M1 areas to assess the resting motor threshold (RMT), short-interval cortical inhibition (SICI), intracortical facilitation (ICF), and the contralateral cortical silent period (CSP).

RESULTS

In SICI and ICF conditions, right M1 stimulation led to significantly higher motor evoked potential ratios in SZ-SUD compared to SZ-NSUD. This suggests lower cortical inhibition and increased ICF in first-episode SZ with previous cannabis abuse. There were no group differences in RMT and CSP duration. Neither were there any significant correlations between psychopathology (as indexed by Positive and Negative Syndrome Scale), disease characteristics, the extent of cannabis abuse, and TMS parameters (SICI, ICF, and CSP).

CONCLUSIONS

Comorbid cannabis abuse may potentiate the reduced intracortical inhibition and enhanced ICF observed in first-episode SZ patients in some previous studies. This finding suggests an increased alteration of GABA(A) and NMDA receptor activity in cannabis-abusing first-episode patients as compared to schizophrenia patients with no history of substance abuse. This may constitute a distinct vulnerability factor in this special population.

Neurophysiological correlates of borderline personality disorder: a transcranial magnetic stimulation study

BACKGROUND

Cortical inhibition deficits have been demonstrated in several disorders with deficits in impulsive control (e.g., attention-deficit/hyperactivity disorder [ADHD], tic disorder, Tourette syndrome) by using transcranial magnetic stimulation (TMS). With borderline personality disorder (BPD), we investigated another disorder associated with high impulsivity by TMS. We hypothesized that BPD patients display decreased cortical inhibition and/or increased cortical excitation as assessed with TMS.

METHODS

Different inhibitory and excitatory TMS parameters were investigated in 19 unmedicated female BPD patients and 19 healthy control subjects matched for sex, age, handedness, and body height. Additionally, the results were controlled for ADHD symptomatology.

RESULTS

A reduced cortical silent period (CSP) duration was found in BPD patients compared with healthy control subjects in the right cortex. Even after controlling for ADHD symptoms, this result remained significant.

CONCLUSIONS

These findings support an association between BPD and cortical inhibition deficits as indexed through TMS. The results are discussed considering basic neurobiological mechanisms that may explain our findings of decreased intracortical inhibition in BPD patients.

Reduced cortical inhibition in first-episode schizophrenia

Disturbances in cortico-cortical and cortico-subcortical circuits in schizophrenia have been described by previous neuroimaging and electrophysiological studies. Transcranial magnetic stimulation (TMS) provides a neurophysiological technique for the measurement of cortical excitability, especially of the motoneural system. Previous studies using paired-pulse TMS to investigate short-interval cortical inhibition (SICI) and intracortical facilitation (ICF), mainly involving chronic schizophrenia patients, have been inconsistent and only one study in first-episode patients has been conducted so far. We assessed SICI (interstimulus interval, ISI, 3 milliseconds, ms) and ICF (ISI 7 ms) in 29 first-episode schizophrenia patients (FE-SZ) with limited exposure to antipsychotic treatment against measures of 28 healthy controls (HC). Amplitudes of motor evoked potentials (MEPs) were measured from the left and right first dorsal interosseus muscle (FDI). The conditioning stimulus was set at 80% intensity of resting motor threshold (RMT) and the test stimulus (TS) was set at an intensity that produced an MEP amplitude of about 1 mV. For SICI conditions, FE-SZ demonstrated significantly higher MEP amplitudes from left motor cortex (right FDI) compared to HC, and for MEPs from right motor cortex (left FDI) a similar trend was observable (FE-SZ 41% vs. HC 21% of TS, p=0.017 for left motor cortex, and FE-SZ 59% vs. HC 31% of TS, p=0.059 for right motor cortex; Mann-Whitney U-test). No significant difference in MEPs could be detected for ICF on either hemisphere. In addition, there was no difference in left and right RMT comparing patients and control subjects. Our result of a reduced SICI in a large sample of well characterized first-episode schizophrenia patients suggests that a GABAergic deficit may be involved in schizophrenic pathophysiology, already early in the disease course, supporting the intracortical dysconnectivity hypothesis.

Neuromuscular plasticity during and following 3 wk of human forearm cast immobilization

Prolonged reductions in muscle activity results in alterations in neuromuscular properties; however, the time course of adaptations is not fully understood, and many of the specific adaptations have not been identified. This study evaluated the temporal evolution of adaptations in neuromuscular properties during and following 3 wk of immobilization. We utilized a combination of techniques involving nerve stimulation and transcranial magnetic stimulation to assess changes in central activation of muscle, along with spinal (H reflex) and corticospinal excitability [i.e., motor-evoked potential (MEP) amplitude, silent period (SP)] and contractile properties in 10 healthy humans undergoing 3 wk of forearm immobilization and 9 control subjects. Immobilization induced deficits in central activation (85 +/- 3 to 67 +/- 7% ) that returned to baseline levels 1 wk after cast removal. The flexor carpii radialis MEP amplitude increased greater than twofold after the first week of immobilization and remained elevated throughout immobilization and 1 wk after cast removal. Additionally, we observed a prolongation of the SP 1 wk after cast removal compared with baseline (78.5 +/- 7.1 to 98.2 +/- 8.7 ms). The contractile properties were also altered, since the rate of evoked force relaxation was slower following immobilization (-14.5 +/- 1.4 to -11.3 +/- 1.0% peak force/ms), and remained depressed 1 wk after cast removal (-10.5 +/- 0.8% peak force/ms). These observations detail the time course of adaptations in corticospinal and contractile properties associated with disuse and illustrate the profound effect of immobilization on the human neuromuscular system as evidenced by the alterations in corticospinal excitability persisting 1 wk following cast removal.

Interhemispheric transfer deficit in alexithymia: a transcranial magnetic stimulation study

BACKGROUND

A deficit in interhemispheric transfer was hypothesized in alexithymia more than 30 years ago, following the observation that split-brain patients manifest certain alexithymic characteristics. However, direct evidence of interhemispheric transfer deficit has never been provided. This study investigated the hypothesis of a transcallosal interhemispheric transfer deficit in alexithymia by means of paired-pulse transcranial magnetic stimulation.

METHODS

A random sample of 300 students was screened for alexithymia using the Italian version of the 20-item Toronto Alexithymia Scale. Eight right-handed males and eight females with high alexithymic scores and an age- and gender-matched group with low alexithymic scores were selected. A first (conditioning) magnetic stimulus was delivered to one motor cortex followed by a second (test) stimulus to the opposite hemisphere at different interstimulus intervals for both motor cortices. Motor evoked responses were recorded from the abductor digit minimi muscles.

RESULTS

High alexithymic subjects showed reduced transcallosal inhibition as compared to low alexithymic subjects at interstimulus intervals of 10, 12 and 14 ms in the left-to-right and right-to-left interhemispheric transfer directions.

CONCLUSIONS

Results point to functional differences in transcallosal interactions in high alexithymic as compared to low alexithymic subjects, supporting the hypothesis of an interhemispheric transfer deficit in alexithymia.

Electronically switchable sham transcranial magnetic stimulation (TMS) system

Transcranial magnetic stimulation (TMS) is increasingly being used to demonstrate the causal links between brain and behavior in humans. Further, extensive clinical trials are being conducted to investigate the therapeutic role of TMS in disorders such as depression. Because TMS causes strong peripheral effects such as auditory clicks and muscle twitches, experimental artifacts such as subject bias and placebo effect are clear concerns. Several sham TMS methods have been developed, but none of the techniques allows one to intermix real and sham TMS on a trial-by-trial basis in a double-blind manner. We have developed an attachment that allows fast, automated switching between Standard TMS and two types of control TMS (Sham and Reverse) without movement of the coil or reconfiguration of the setup. We validate the setup by performing mathematical modeling, search-coil and physiological measurements. To see if the stimulus conditions can be blinded, we conduct perceptual discrimination and sensory perception studies. We verify that the physical properties of the stimulus are appropriate, and that successive stimuli do not contaminate each other. We find that the threshold for motor activation is significantly higher for Reversed than for Standard stimulation, and that Sham stimulation entirely fails to activate muscle potentials. Subjects and experimenters perform poorly at discriminating between Sham and Standard TMS with a figure-of-eight coil, and between Reverse and Standard TMS with a circular coil. Our results raise the possibility of utilizing this technique for a wide range of applications.

[Cortical excitability in schizophrenia. Studies using transcranial magnetic stimulation]

Abnormalities in brain plasticity, including abnormal information processing by disturbed cortical inhibition and facilitation in schizophrenia, have been described several times in the past. Transcranial magnetic stimulation (TMS) provides a neurophysiological technique for the measurement of cortical excitability, especially of the motoneural system. With TMS it is possible to explore important aspects of the pathophysiological mechanisms underlying schizophrenia using recently developed paradigms (paired pulse method, cortical silent period). This review summarizes the results of available diagnostic TMS studies in schizophrenia. Studies investigating the efficacy of therapeutic repetitive magnetic stimulation in patients with treatment resistant hallucinations or predominantly negative symptoms were not considered. The reviewed studies support the assumption of reduced cortical inhibition, probably caused by GABAergic deficit, in schizophrenia. Factors influencing the study results, the limitations of this promising technique in schizophrenia, and further research options are discussed.

A rapid sound-action association effect in human insular cortex

Background

Learning to play a musical piece is a prime example of complex sensorimotor learning in humans. Recent studies using electroencephalography (EEG) and transcranial magnetic stimulation (TMS) indicate that passive listening to melodies previously rehearsed by subjects on a musical instrument evokes differential brain activation as compared with unrehearsed melodies. These changes were already evident after 20–30 minutes of training. The exact brain regions involved in these differential brain responses have not yet been delineated.

Methodology/Principal Finding

Using functional MRI (fMRI), we investigated subjects who passively listened to simple piano melodies from two conditions: In the ‘actively learned melodies’ condition subjects learned to play a piece on the piano during a short training session of a maximum of 30 minutes before the fMRI experiment, and in the ‘passively learned melodies’ condition subjects listened passively to and were thus familiarized with the piece. We found increased fMRI responses to actively compared with passively learned melodies in the left anterior insula, extending to the left fronto-opercular cortex. The area of significant activation overlapped the insular sensorimotor hand area as determined by our meta-analysis of previous functional imaging studies.

Conclusions/Significance

Our results provide evidence for differential brain responses to action-related sounds after short periods of learning in the human insular cortex. As the hand sensorimotor area of the insular cortex appears to be involved in these responses, re-activation of movement representations stored in the insular sensorimotor cortex may have contributed to the observed effect. The insular cortex may therefore play a role in the initial learning phase of action-perception associations.

"Getting physical": the management of neuropsychiatric disorders using novel physical treatments

OBJECTIVE

To summarize and review the utility of physical interventions in the treatment of psychiatric disorders.

METHODS

A systematic review of the literature pertaining to novel physical interventions, namely, transcranial magnetic stimulation, deep brain stimulation, vagus nerve stimulation, and neurosurgery, was conducted using MEDLINE, EMBASE, and PSYCHLIT. Bibliographies of papers were scrutinized for further relevant references along with literature known to the authors.

RESULTS

Currently available physical interventions worldwide are reviewed with respect to efficacy, applications, and putative indications. Physical interventions have experienced a resurgence of interest for both the investigation of brain function and the treatment of neuropsychiatric disorders. The widespread availability of neuroimaging technology has advanced our understanding of brain function and allowed closer examination of the effects of physical treatments. Clinically, transcranial magnetic stimulation seems likely to have a role in the management of depression, and its use in other neuropsychiatric disorders appears promising. Following on from its success in the management of intractable epilepsy, vagus nerve stimulation is undergoing evaluation in the treatment of depression with some success in refractory cases. Deep brain stimulation has improved mood in patients with Parkinson's disease and may also relieve symptoms of obsessive-compulsive disorder. Neurosurgery has re-invented itself by way of increased technical sophistication, and although further assessment of its efficacy and clinical utility is still needed, its widespread practice reflects its increasing acceptance as a viable treatment of last resort.

CONCLUSION

It is clear that physical treatments are here to stay and "getting physical" offers a useful addition to the neuropsychiatrist's therapeutic armamentarium. However, like all new treatments these interventions need to remain under rigorous scientific scrutiny to determine accurately their immediate and long-term effects.

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

Repetitive transcranial magnetic stimulation (rTMS) holds promise as a therapeutic tool in major depression. However, a means to assess the effects of a single rTMS session on mood to guide subsequent sessions would be desirable. The present study examined the effects of a single rTMS session on an affective go/no-go task known to measure emotional-cognitive deficits associated with major depression. Ten patients with an acute episode of unipolar major depression and eight partially or completely remitted (improved) patients underwent 1 Hz rTMS over the left and right dorsolateral prefrontal cortex prior to task performance. TMS over the mesial occipital cortex was used as a control. We observed significantly improved performance in depressed patients following right prefrontal rTMS. This beneficial effect declined with decreasing depression severity and tended to reverse in the improved group. Left prefrontal rTMS had no significant effect in the depressed group, but it resulted in impaired task performance in the improved group. Our findings indicate that the acute response of depressed patients to rTMS varies with the stimulation site and depression severity. Further studies are needed to determine whether the present paradigm could be used to predict antidepressant treatment success or to individualize stimulation parameters according to specific pathology.

Depressed mood, index finger force and motor cortex stimulation: a transcranial magnetic stimulation (TMS) study

The present study utilized transcranial magnetic stimulation (TMS) of the motor cortex to understand basic motor processes associated with depressive symptoms independent of cognitive requirements or diagnostic category. To assess the integrity of the basic cortical-spinal-motor circuit associated with depressed mood, TMS to the motor cortex was used to initiate motor evoked potentials (MEPs) in forearm EMG and force production measured in the right (dominant) index finger. While at rest, a group with more depressive symptoms showed less force response in the index finger following stimulations compared with a group endorsing less depressive symptoms. A negative correlation between force response in the index finger at baseline (rest) following stimulation and the Beck depression inventory indicated that depressive mood symptom elevations were associated with less response to stimulations. The results argue for a greater importance placed on the relationship between depressive mood symptoms and basic motor processes.

Repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex and cortical excitability in patients with major depressive disorder

Repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex is a relatively non-invasive technique with putative therapeutic effects in major depression. However, the exact neurophysiological basis of these effects needs further clarification. Therefore, we studied the impact of ten daily sessions of left, dorsolateral prefrontal rTMS on motor cortical excitability, as revealed by transcranial magnetic stimulation-elicited motor-evoked potentials in 30 patients. As compared to the non-responders, responders (33%) showed changes in parameters pointing towards a reduced cortical excitability. These results suggest that repetitive transcranial magnetic stimulation of the dorsolateral, prefrontal cortex may have inhibitory effects on motor cortical neuronal excitability in patients with major depressive disorder. Furthermore, measurement of motor cortical excitability may be a useful tool for investigating and monitoring inhibitory brain effects of antidepressant stimulation techniques like rTMS.

Functional imaging and the neural systems of chronic pain

Pain remains a serious health care problem affecting millions of individuals, costing billions of dollars, and causing an immeasurable amount of human suffering. In designing improved therapies, there is still much to learn about peripheral nociceptor, nerves, and the spinal cord, and brain stem modulatory systems. Nevertheless, it is the brain that presents us with an incredible opportunity to understand the experience we call pain. Functional neuroimaging is helping to unlock the secrets of the sensory and emotional components of pain and its autonomic responses. These techniques are helping us to understand that pain is not a static disease with the pathologic findings localized to the periphery but is instead a highly plastic condition affecting multiple central neural systems. Functional neuroimaging is transforming our understanding of the neurobiology of pain and will be instrumental in helping us to design more rational treatments ultimately aimed at reducing the impact of pain on our patients. It is opening windows into the function of the brain that were previously closed.