Antidepressant outcomes of high-frequency repetitive transcranial magnetic stimulation (rTMS) with F8-coil and deep transcranial magnetic stimulation (DTMS) with H1-coil in major depression: a systematic review and meta-analysis

Deep transcranial magnetic stimulation for adolescents with treatment-resistant depression: Behavioral and neural correlates of clinical improvement

BACKGROUND

Affective bias toward negativity is associated with depression and may represent a promising treatment target. Stimulating the dorsolateral prefrontal cortex (dlPFC) with deep Transcranial Magnetic Stimulation (dTMS) could lead to shifts in affective bias. The current study examined behavioral and neural correlates of affective bias in the context of dTMS in adolescents with treatment-resistant depression (TRD).

METHODS

Adolescents completed a Word-Face Stroop (WFS) task during an fMRI scan before and after 30 sessions of dTMS targeting the left dlPFC. In the task, participants were shown words superimposed on faces in either a "congruent" (both word and face were positive or both negative) or an "incongruent" fashion; in both cases, participants identified whether the words were positive or negative. We examined pre-post intervention neural and behavioral WFS changes and their correlations with clinical improvement.

RESULTS

Usable pre- and post-intervention WFS data were available for 10 adolescents with TRD (Age, years: M = 16.3, SD = 1.09) for behavioral data; 9 for neuroimaging data. After treatment, although changes in behavioral performance did not suggest improved affective bias, amygdala activation decreased during the negative word/happy face condition, which correlated with clinical improvement. Overall, clinical improvement correlated with decreased neural activation during congruent conditions.

LIMITATIONS

Major limitations include the small sample size, lack of a sham control group, and unknown psychometric properties.

CONCLUSIONS

Preliminary findings suggesting improving neural efficiency and normalizing affective bias in those with the most clinical improvement highlight the potential importance of targeting affective bias in treating adolescents with TRD.

Consensus review and considerations on TMS to treat depression: A comprehensive update endorsed by the National Network of Depression Centers, the Clinical TMS Society, and the International Federation of Clinical Neurophysiology

This article updates the prior 2018 consensus statement by the National Network of Depression Centers (NNDC) on the use of transcranial magnetic stimulation (TMS) in the treatment of depression, incorporating recent research and clinical developments. Publications on TMS and depression between September 2016 and April 2024 were identified using methods informed by PRISMA guidelines. The NNDC Neuromodulation Work Group met monthly between October 2022 and April 2024 to define important clinical topics and review pertinent literature. A modified Delphi method was used to achieve consensus. 2,396 abstracts and manuscripts met inclusion criteria for review. The work group generated consensus statements which include an updated narrative review of TMS safety, efficacy, and clinical features of use for depression. Considerations related to training, roles/responsibilities of providers, and documentation are also discussed. TMS continues to demonstrate broad evidence for safety and efficacy in treating depression. Newer forms of TMS are faster and potentially more effective than conventional repetitive TMS. Further exploration of targeting methods, use in special populations, and accelerated protocols is encouraged. This article provides an updated overview of topics relevant to the administration of TMS for depression and summarizes expert, consensus opinion on the practice of TMS in the United States.

The effect of repetitive and Deep Transcranial Magnetic Stimulation on quantitative electroencephalography in major depressive disorder

Background

F-8-coil repetitive transcranial magnetic stimulation (rTMS) and H-1-coil deep repetitive transcranial magnetic stimulation (dTMS) have been indicated for the treatment of major depressive disorder (MDD) in adult patients by applying different treatment protocols. Nevertheless, the evidence for long-term electrophysiological alterations in the cortex following prolonged TMS interventions, as assessed by quantitative electroencephalography (qEEG), remains insufficiently explored. This study aims to demonstrate the qEEG-based distinctions between rTMS and dTMS in the management of depression and to evaluate the potential correlation between the electrophysiological changes induced by these two distinct TMS interventions and the clinical improvement in depressive and anxiety symptoms.

Methods

A total of 60 patients diagnosed with treatment resistant depression received rTMS (n = 30) or dTMS (n = 30) along with their usual treatments in Kemal Arıkan Psychiatry Clinic. All the participants underwent resting-state qEEG recording before and at the end of 30 sessions of TMS treatment. The significant qEEG changes were then tested for their correlation with the improvement in depression and anxiety.

Results

After the course of rTMS and dTMS a considerable reduction is seen in the severity of depression and anxiety. Although improvements in depression and anxiety were observed in both TMS groups, specific neural activity patterns were associated with better outcomes in depression. Patients who exhibited lower alpha activity in the left fronto-central region and higher gamma activity in the right prefrontal region following rTMS showed more significant improvements in depression symptoms. Similarly, those whose beta activity increased in the left prefrontal region but decreased in the right prefrontal region after rTMS tended to have greater reductions in depression and anxiety severity. For patients in the dTMS group, those who demonstrated a decrease in left temporal theta activity after treatment were more likely to experience a substantial improvement in depression severity.

Conclusion

Following 30 sessions of rTMS with a F8 coil and dTMS with an H1 coil, notable alterations in qEEG activity with clinical significance were discerned. The persistence of these changes should be investigated in the subsequent follow-up period.

Royal Australian and New Zealand College of Psychiatrists professional practice guidelines for the administration of repetitive transcranial magnetic stimulation

OBJECTIVES

To provide guidance for the optimal administration of repetitive transcranial magnetic stimulation, based on scientific evidence and supplemented by expert clinical consensus.

METHODS

Articles and information were sourced from existing guidelines and published literature. The findings were then formulated into consensus-based recommendations and guidance by the authors. The guidelines were subjected to rigorous successive consultation within the RANZCP, involving the Section of ECT and Neurostimulation (SEN) Committee, its broader membership and expert committees.

RESULTS

The RANZCP professional practice guidelines (PPG) for the administration of rTMS provide up-to-date advice regarding the use of rTMS in clinical practice. The guidelines are intended for use by psychiatrists and non-psychiatrists engaged in the administration of rTMS to facilitate best practice to optimise outcomes for patients. The guidelines strive to find the appropriate balance between promoting best evidence-based practice and acknowledging that evidence for rTMS use is a continually evolving.

CONCLUSION

The guidelines provide up-to-date advice for psychiatrists and non-psychiatrists to promote optimal standards of rTMS practice.

Deep transcranial magnetic stimulation for adolescents with treatment-resistant depression: A preliminary dose-finding study exploring safety and clinical effectiveness

BACKGROUND

Transcranial magnetic stimulation (TMS) is an intervention for treatment-resistant depression (TRD) that modulates neural activity. Deep TMS (dTMS) can target not only cortical but also deeper limbic structures implicated in depression. Although TMS has demonstrated safety in adolescents, dTMS has yet to be applied to adolescent TRD.

OBJECTIVE/HYPOTHESIS

This pilot study evaluated the safety, tolerability, and clinical effects of dTMS in adolescents with TRD. We hypothesized dTMS would be safe, tolerable, and efficacious for adolescent TRD.

METHODS

15 adolescents with TRD (Age, years: M = 16.4, SD = 1.42) completed a six-week daily dTMS protocol targeting the left dorsolateral prefrontal cortex (BrainsWay H1 coil, 30 sessions, 10 Hz, 3.6 s train duration, 20s inter-train interval, 55 trains; 1980 total pulses per session, 80 % to 120 % of motor threshold). Participants completed clinical, safety, and neurocognitive assessments before and after treatment. The primary outcome was depression symptom severity measured by the Children's Depression Rating Scale-Revised (CDRS-R).

RESULTS

14 out of 15 participants completed the dTMS treatments. One participant experienced a convulsive syncope; the other participants only experienced mild side effects (e.g., headaches). There were no serious adverse events and minimal to no change in cognitive performance. Depression symptom severity significantly improved pre- to post-treatment and decreased to a clinically significant degree after 10 treatment sessions. Six participants met criteria for treatment response.

LIMITATIONS

Main limitations include a small sample size and open-label design.

CONCLUSIONS

These findings provide preliminary evidence that dTMS may be tolerable and associated with clinical improvement in adolescent TRD.

Functional connectivity analysis of the depression connectome provides potential markers and targets for transcranial magnetic stimulation

BACKGROUND

Despite efforts to improve targeting accuracy of the dorsolateral prefrontal cortex (DLPFC) as a repetitive transcranial magnetic stimulation (rTMS) target for Major Depressive Disorder (MDD), the heterogeneity in clinical response remains unexplained.

OBJECTIVE

We sought to compare the patterns of functional connectivity from the DLPFC treatment site in patients with MDD who were TMS responders to those who were TMS non-responders.

METHODS

Baseline anatomical T1 magnetic resonance imaging (MRI), resting-state functional MRI, and diffusion weighted imaging scans were obtained from 37 participants before they underwent a course of rTMS to left Brodmann area 46. A novel machine learning method was utilized to identify brain regions associated with each item of the Beck's Depression Inventory II (BDI-II), and for 26 participants who underwent rTMS treatment over the left Brodmann area 46, identify regions differentiating rTMS responders and non-responders.

RESULTS

Nine parcels of the Human Connectome Project Multimodal Parcellation Atlas matched to at least three items of the Beck's Depression Inventory II (BDI-II) as predictors of response to rTMS, with many in the temporal, parietal and cingulate cortices. Additionally, pre-treatment mapping for 17 items of the BDI-II demonstrated significant variability in symptom to parcel mapping. When parcels associated with symptom presence and symptom resolution were compared, 15 parcels were uniquely associated with resolution (potential targets), and 12 parcels were associated with both symptom presence and resolution (blockers or biomarkers).

CONCLUSIONS

Machine learning approaches show promise for the development of pathoanatomical diagnosis and treatment algorithms for MDD. Prospective studies are required to facilitate clinical translation.

Efficacy and safety of transcranial magnetic stimulation for treating major depressive disorder: An umbrella review and re-analysis of published meta-analyses of randomised controlled trials

OBJECTIVES

We re-analysed data from published meta-analyses testing the effects of Transcranial Magnetic Stimulation (TMS) on Major Depressive Disorder (MDD) in adults. We applied up-to-date meta-analytic techniques for handling heterogeneity including the random-effects Hartung-Knapp-Sidik-Jonkman method and estimated 95% prediction intervals. Heterogeneity practices in published meta-analyses were assessed as a secondary aim.

STUDY DESIGN AND SETTING

We performed systematic searches of systematic reviews with meta-analyses that included randomised controlled trials assessing the efficacy, tolerability, and side effects of TMS on MDD. We performed risk of bias assessment using A MeaSurement Tool to Assess Reviews (AMSTAR) 2 and re-analysed meta-analyses involving 10 or more primary studies.

RESULTS

We included 29 systematic reviews and re-analysed 15 meta-analyses. Authors of all meta-analyses interpreted findings to suggest TMS is safe and effective for MDD. Our re-analysis showed that in 14 out of 15 meta-analyses, the 95% prediction intervals included the null and captured values in the opposite effect direction. We also detected presence of small-study effects in some meta-analyses and 24 out of 25 systematic reviews received an AMSTAR 2 rating classed as critically low.

CONCLUSION

Authors of all included meta-analyses interpreted findings to suggest TMS is safe and effective for MDD despite lack of comprehensive investigation of heterogeneity. Our re-analysis revealed the direction and magnitude of treatment effects vary widely across different settings. We also found high risk of bias in the majority of included systematic reviews and presence of small-study effects in some meta-analyses. Because of these reasons, we argue TMS for MDD may not be as effective and potentially less tolerated in some populations than current evidence suggests.

Efficacy and tolerability of repetitive transcranial magnetic stimulation for late-life depression: A systematic review and meta-analysis

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a widely available treatment for major depression, but its efficacy and tolerability are uncertain for patients with late-life depression (LLD). To assess the existing evidence of rTMS for LLD treatment, we conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) according to PRISMA guidelines.

METHODS

We retrieved RCTs from four databases published between 1 January 2000 and 10 September 2021 comparing the effects of active and sham stimulation in LLD patients. We performed subgroup analyses to examine the impact of different parameters. The primary outcomes were the response and discontinuation rates of rTMS for LLD patients, representing for efficacy and tolerability, respectively. Secondary outcomes were remission and dropout rates. Discontinuation referred to patients who withdrew for any reason, while dropout referred to participants who withdrew early because of adverse events.

RESULTS

Nine articles describing 11 studies (two articles each contained two studies) met the eligibility criteria. All outcomes were analyzed using a random-effects model. The summary analysis of nine suitable RCTs revealed a cumulative response rate of 2.86 (95 % confidence interval (95 % CI), 1.87-4.37) and a remission rate of 4.02 (95 % CI, 1.83-8.81) in the active group compared to the sham group. The pooled odds ratios (ORs) for discontinuation and dropout rates were not significantly different between the two groups. In addition, some rTMS parameters were associated with better efficacy.

CONCLUSIONS

The meta-analysis suggested that rTMS is an effective, well-tolerated treatment for patients with LLD. Future efforts should enhance study methodologies to improve their efficacy and increase the homogeneity of rTMS parameters to promote comparability between studies.

The functional connectivity predictor of therapeutic effect of continuous theta burst stimulation on obsessive-compulsive disorder: A preliminary study

OBJECTIVE

To evaluate the efficacy of continuous theta burst stimulation (cTBS) on the bilateral supplementary motor area (SMA) among patients with obsessive-compulsive disorder (OCD) and to explore the potential predictors of cTBS outcome based on neuroimaging.

METHODS

29 OCD patients and 29 healthy controls (HCs) were enrolled in this pilot study. Twenty consecutive cTBS intervention targeting at bilateral SMA was applied. MRI scan was carried out before cTBS and 15 regions in the executive control and sensorimotor network were chosen and analyzed using MATLAB, DPABI, and SPM12.

RESULTS

11 out of 29 patients responded to cTBS (37.93%), and the clinical symptom of OCD patients was significantly relieved after receiving regular cTBS. Also, the FC between Cerebelum_Crus2_L and Frontal_Inf_Tri_L of OCD patients showed positive prognosis for the efficacy of cTBS, with the area under the curve (AUC) of 0.85 (95% confidence interval: 0.718-0.989, p = 0.002). None of the patients had any serious adverse event.

CONCLUSION

cTBS intervention on bilateral SMA can significantly improve the symptoms of medicated OCD patients with moderate severity. And the pretherapy FC could be a valuable potential predictor of the cTBS treatment outcome among OCD patients.

Evidence and expert consensus based German guidelines for the use of repetitive transcranial magnetic stimulation in depression

INTRODUCTION

Non-invasive brain stimulation techniques such as repetitive transcranial magnetic stimulation (rTMS) offer a promising alternative to psychotherapeutic and pharmacological treatments for depression. This paper aims to present a practical guide for its clinical implementation based on evidence from the literature as well as on the experience of a group of leading German experts in the field.

METHODS

The current evidence base for the use of rTMS in depression was examined via review of the literature. From the evidence and from clinical experience, recommendations for the use of rTMS in clinical practice were derived. All members of the of the German Society for Brain Stimulation in Psychiatry and all members of the sections Clinical Brain Stimulation and Experimental Brain Stimulation of the German Society for Psychiatry, Psychotherapy, Psychosomatics and Mental Health were invited to participate in a poll on whether they consent with the recommendations.

FINDINGS

Among rTMS experts, a high consensus rate could be identified for clinical practice concerning the setting and the technical parameters of rTMS treatment in depression, indications and contra-indications, the relation of rTMS to other antidepressive treatment modalities and the frequency and management of side effects.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Repetitive Transcranial Magnetic Stimulation: Influence on Stress and Early Responsiveness Outcomes for Depression, Anxiety, and Stress

The present study investigated whether rTMS treatment for depression reduced stress and whether early responsiveness of rTMS predicted outcomes for depression, anxiety, and stress at the conclusion of treatment. Participants (n = 109) were inpatients at a psychiatric hospital referred for rTMS for depression. Linear mixed models were used to analyse data across time and regression analyses were used to assess early responsiveness. Effect sizes, and clinically significant and reliable change were also analysed. Decreases in scores for depression, anxiety, and stress were evident from pre- to mid-treatment, and from mid- to post-treatment. Large effect sizes were reported from pre- to post-treatment for depression and stress. Changes in depression from pre- to mid-treatment predicted post-treatment depression and stress scores. Clinically significant change was most common for stress and reliable change was most common for depression. Standard rTMS treatment for depression appears to have non-specific benefits in that participant anxiety and stress ratings also improve significantly. Early improvements in depressive symptoms may be indicative of later depression and stress outcomes, suggesting clinical benefit in assessing outcomes during rTMS treatment.

Effectiveness of noninvasive brain stimulation in the treatment of anxiety disorders: a meta-analysis of sham or behaviour-controlled studies

BACKGROUND

The possibility of using noninvasive brain stimulation to treat mental disorders has received considerable attention recently. Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are considered to be effective treatments for depressive symptoms. However, no treatment recommendation is currently available for anxiety disorders, suggesting that evidence is still limited. We conducted a systematic review of the literature and a quantitative analysis of the effectiveness of rTMS and tDCS in the treatment of anxiety disorders.

METHODS

Following PRISMA guidelines, we screened 3 electronic databases up to the end of February 2020 for English-language, peer-reviewed articles that included the following: a clinical sample of patients with an anxiety disorder, the use of a noninvasive brain stimulation technique, the inclusion of a control condition, and pre/post scores on a validated questionnaire that measured symptoms of anxiety.

RESULTS

Eleven papers met the inclusion criteria, comprising 154 participants assigned to a stimulation condition and 164 to a sham or control group. We calculated Hedge's g for scores on disorder-specific and general anxiety questionnaires before and after treatment to determine effect size, and we conducted 2 independent random-effects meta-analyses. Considering the well-known comorbidity between anxiety and depression, we ran a third meta-analysis analyzing outcomes for depression scores. Results showed a significant effect of noninvasive brain stimulation in reducing scores on disorder-specific and general anxiety questionnaires, as well as depressive symptoms, in the real stimulation compared to the control condition.

LIMITATIONS

Few studies met the inclusion criteria; more evidence is needed to strengthen conclusions about the effectiveness of noninvasive brain stimulation in the treatment of anxiety disorders.

CONCLUSION

Our findings showed that noninvasive brain stimulation reduced anxiety and depression scores compared to control conditions, suggesting that it can alleviate clinical symptoms in patients with anxiety disorders.

Clinical effectiveness of non-TMS neurostimulation in depression: Clinical trials from 2010 to 2020

OBJECTIVE

Treatment for major depressive disorder (MDD) have evolved, although there is still a strong unmet need for more effective and tolerable options. The present study summarizes and discusses recent evidence regarding the non-transcranial magnetic stimulation (non-TMS) neurostimulation treatment for MDD.

METHODS

The authors reviewed non-TMS neurostimulation clinical trials for MDD between 2010 and 2020. Electroconvulsive therapy was not included in this review. A systematic review was performed in MEDLINE database through PubMed, the Cochrane Collaboration's Clinical Trials Register (CENTRAL), PsycINFO and Thomson Reuters's Web of Science.

RESULTS

Only 20 articles met the inclusion criteria. Randomized controlled trials demonstrated efficacy of transcranial direct current stimulation (tDCS) in five of seven trials. tDCS augmented with sertraline, fluoxetine, citalopram and escitalopram was superior to placebo and to tDCS only. A comparative trial demonstrated that the duration of tDCS sessions can modulate the effectiveness of this treatment. Open trials indicated that deep brain stimulation, epidural cortical stimulation, trigeminal nerve stimulation, magnetic seizure therapy and vagus nerve stimulation may be effective in treatment-resistant depression.

CONCLUSION

This review confirmed the efficacy of tDCS in MDD. Despite new evidence showing effectiveness for other non-TMS neurostimulation, their effectiveness is still unclear. Non-TMS neurostimulation RCTs with large samples and head-to-head studies comparing non-TMS neurostimulation and gold standard pharmacological treatments are still lacking.

A Preliminary Study of Adjunctive Nonconvulsive Electrotherapy for Treatment-Refractory Depression

Nonconvulsive electrotherapy (NET) defined as electrical brain stimulation administered like standard electroconvulsive therapy (ECT), but below seizure threshold, could be effective for patients with treatment-refractory depression (TRD) with fewer adverse neurocognitive outcomes. However, there is a lack of studies in Chinese patients with TRD. Thus, this study was conducted to examine the efficacy and safety of adjunctive NET for Chinese patients with TRD. Twenty TRD patients were enrolled and underwent six NET treatments. Depressive symptoms, response, and remission were assessed with the 17-item Hamilton Depression Rating Scale (HAMD-17) at baseline and after 1, 3, and 6 NET treatments. Neurocognitive function was assessed by the Wisconsin Card Sorting Test (WCST) at baseline and after the completion of six NET treatments. Mean HAMD-17 scores declined significantly from 26.2 to 10.4 (p < 0.001) after post-NET. The rates of response and remission were 60.0% (95% CI: 36.5-83.5) and 10.0% (95% CI: 0-24.4), respectively. Neurocognitive performance improved following a course of NET. No significant association was found between changes in depressive symptoms and baseline neurocognitive function. Adjunctive NET appeared to be effective for patients with TRD, without adverse neurocognitive effects. Randomized controlled studies were warranted to confirm these findings.

Repetitive transcranial magnetic stimulation for major depressive disorder: basic principles and future directions

Repetitive transcranial magnetic stimulation (rTMS) is a safe and well-tolerated intervention for major depressive disorder (MDD). Over 150 randomized controlled trials (RCTs) have been carried out, and its efficacy has been confirmed in dozens of meta-analyses. Real world data has also confirmed the effectiveness of rTMS for MDD in clinical practice, with the most recent literature indicating response rates of 40-50% and remission rates of 25-30%. In this review, we first offer an historical perspective, followed by a review of basic principles, such as putative mechanisms, procedures and protocols, stimulation targets, efficacy and durability of response, side effects, and the placebo controversy. In the second part of this review, we first discuss solutions to increase accessibility to rTMS, such as modifications to treatment equipment, protocols and setting. We continue with possible means to further increase effectiveness, such as treatment personalization and extension. We conclude by addressing the scheduling issue, with accelerated rTMS (arTMS) as a possible solution.

An update on the clinical use of repetitive transcranial magnetic stimulation in the treatment of depression

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is an increasingly used treatment for patients with depression. The use of rTMS in depression is supported by over 20 years of clinical trials. There has been a significant increase in knowledge around the use of rTMS in recent years.

OBJECTIVE

The aim of this paper was to review the use of rTMS in depression to provide an update for rTMS practitioners and clinicians interested in the clinical use of this treatment.

METHODS

A targeted review of the literature around the use of rTMS treatment of depression with a specific focus on studies published in the last 3 years.

RESULTS

High-frequency rTMS applied to the left dorsolateral prefrontal cortex is an effective treatment for acute episodes of major depressive disorder. There are several additional methods of rTMS delivery that are supported by clinical trials and meta-analyses but no substantive evidence that any one approach is any more effective than any other. rTMS is effective in unipolar depression and most likely bipolar depression. rTMS courses may be repeated in the management of depressive relapse but there is less evidence for the use of rTMS in the maintenance phase.

CONCLUSIONS

The science around the use of rTMS is rapidly evolving and there is a considerable need for practitioners to remain abreast of the current state of this literature and its implications for clinical practice. rTMS is an effective antidepressant treatment but its optimal use should be continually informed by knowledge of the state of the art.