Enhancement of motor learning by focal intermittent theta burst stimulation (iTBS) of either the primary motor (M1) or somatosensory area (S1) in healthy human subjects

The effects of combining sensorimotor training with transcranial direct current stimulation on the anticipatory and compensatory postural adjustments in patients with chronic low back pain

PURPOSE

To investigate the effects of concurrent sensorimotor training (SMT) and transcranial direct current stimulation (tDCS) on the anticipatory and compensatory postural adjustments (APAs and CPAs) in patients with chronic low back pain (CLBP).

METHOD

The interventions included (1) SMT plus tDCS and (2) SMT plus sham tDCS. Outcome measures were the normalized integrals of electromyography activity (NIEMG) during the phases of anticipatory and compensatory, and muscle onset latency. The investigated muscles were ipsilateral and contralateral multifidus (MF), transversus abdominus/internal oblique (TrA/IO), and gluteus medius (GM).

RESULTS

Between-group comparisons demonstrated that ipsilateral TrA/IO NIEMG during CPA1 (p = 0.010) and ipsilateral GM NIEMG during CPA1 (p = 0.002) and CPA2 (p = 0.025) were significantly lower in the SMT combined with tDCS than in the control group. Furthermore, this group had greater NIEMG for contralateral GM during APA1 than the control group (p = 0.032). Moreover, the onset latency of contralateral TrA/IO was significantly earlier after SMT combined with tDCS (p = 0.011).

CONCLUSIONS

Both groups that received SMT showed positive effects, but anodal tDCS had an added value over sham stimulation for improving postural control strategies in patients with CLBP. Indeed, SMT combined with tDCS leads to stronger APA and less demand for CPA.

RCT REGISTRATION NUMBER

IRCT20220228054149N1.

REGISTRATION DATE

2022-04-04.

Effects of combining sensory-motor exercises with transcranial direct current stimulation on cortical processing and clinical symptoms in patients with lumbosacral radiculopathy: An exploratory randomized controlled trial

BACKGROUND

Chronic low back pain (CLBP) is linked to reduced excitability in the primary motor (M1) and sensory (S1) cortices. Combining sensory-motor exercises with transcranial direct current stimulation (tDCS) to boost M1 and S1 excitability may improve treatment outcomes. This combined approach aligns with the neurophysiological mechanisms underlying CLBP and may target the neuroplastic changes induced by low back pain. This study aimed to assess whether enhancing M1 and S1 excitability via tDCS, alongside sensory-motor exercises, offers additional benefits for CLBP patients.

METHOD

Participants were randomly assigned to receive either real or sham tDCS alongside sensory-motor exercises. Outcome measures included pain intensity, disability level, motor control ability, amplitudes of N80 and N150, and the amplitude of motor-evoked potential (MEP) and active motor threshold (AMT) for the multifidus (MF) and transversus abdominis/internal oblique (TrA/IO) muscles. A linear mixed-effects model (LMM) analyzed group, time, and interaction effects, while Spearman's correlation assessed relationships between neurophysiological and clinical outcomes.

RESULTS

The results showed significant reductions in pain intensity and disability levels (P < 0.001) and improved motor control (P < 0.001) in both groups. Both groups also exhibited increase in MF MEP amplitude (P = 0.042) and N150 amplitude (P = 0.028). The tDCS group demonstrated a significant decrease in AMT of MF and TrA/IO muscles (P < 0.05) and an increase in N80 amplitude (P = 0.027), with no significant changes in the control group. Additionally, the tDCS group had significantly lower AMT for the TrA/IO muscle in the post-test compared to the sham group (P = 0.001). Increased N150 amplitude was correlated with improved motor control.

CONCLUSIONS

The findings showed that sensory-motor exercises combined with either tDCS or sham tDCS effectively reduced pain intensity, decreased disability, and improved lumbar motor control in lumbosacral radiculopathy patients. No significant differences were observed between groups, indicating no added clinical benefit from tDCS over exercises alone. However, both groups demonstrated increased N150 and MF MEP amplitudes, suggesting enhanced cortical excitability in motor and sensory regions. While clinical outcomes were similar, neurophysiological data indicate that sensory-motor exercises play a central role in boosting cortical excitability, with tDCS further amplifying this effect, as evidenced by a significant AMT reduction in MF and TrA/IO muscles and an increase in N80 amplitude.

Global research hotspots and trends of theta burst stimulation from 2004 to 2023: a bibliometric analysis

Background

Theta burst stimulation (TBS) has garnered widespread attention in the scientific community, but a comprehensive bibliometric analysis of TBS research remains absent. This study aims to fill this gap by elucidating the characteristics, hotspots, and trends in TBS publications over the past 20 years using bibliometric methods.

Methods

We retrieved TBS-related publications from January 1, 2004, to December 31, 2023, from the Web of Science Core Collection (WoSCC). The analysis focused on articles and review articles. Data were processed using the bibliometric package in R software, and CiteSpace and VOSviewer were employed for bibliometric and knowledge mapping analyses.

Results

A total of 1,206 publications were identified, with 858 included in the analysis. The annual publication volume showed a fluctuating upward trend. Leading institutions and authors were predominantly from the United States of America (USA) and European countries. Core journals and publications also primarily originated from these regions. Current research hotspots include the clinical applications and mechanisms of TBS in neurorehabilitation and depression. TBS cerebellar stimulation has emerged as a promising therapeutic target. Future research is likely to focus on dysphagia, cognitive impairments, and post-traumatic stress disorder.

Conclusion

This bibliometric analysis provides an overview of the basic knowledge structure, research hotspots, and development trends in TBS research over the past two decades. The findings offer valuable insights into the evolving landscape of TBS research and its potential directions.

The Effectiveness of Intermittent Theta Burst Stimulation for Stroke Patients With Upper Limb Impairments: A Systematic Review and Meta-Analysis

Background

Upper limb impairments are one of the most common health problems of stroke, affecting both motor function and independence in daily life. It has been demonstrated that intermittent theta burst stimulation (iTBS) increases brain excitability and improves upper limb function. Our study sought to determine the role of iTBS in stroke recovery.

Objective

The purpose of this study was to determine the efficacy of iTBS in individuals with upper limb impairments following stroke.

Methods

The databases used included Cumulative Index to PubMed, EMBASE, ESCBOhost, The Cochrane Library, Chinese Biomedical Database, Web of Science, China Biology Medicine (CBM), China National Knowledge Infrastructure (CNKI), Technology Periodical Database (VIP), and WanFang Database. Studies published before November 2021 were included. Each participant received an iTBS-based intervention aimed at improving activity levels or impairment, which was compared to usual care, a sham intervention, or another intervention. The primary outcome measure was a change in upper limb function assessment. Secondary outcomes included impairment, participation, and quality of life measures.

Result

A total of 18 studies (n = 401 participants) that met the inclusion criteria were included in this study. There was a slight change in the upper limb function of the iTBS group compared with the control group, as measured by the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) score (mean difference 2.70, 95% CI −0.02 to 5.42, p = 0.05). Significant improvement in resting motor threshold (RMT) and motor-evoked potential (MEP) was also observed in the meta-analysis of iTBS (MD 3.46, 95% CI 2.63 to 4.28, p < 0.00001); (MD 1.34, 95% CI 1.17 to 1.51, P < 0.00001). In addition, we got similar results when the studies were using the Modified Barthel Index (MBI) assessment (mean difference of 7.34, 95% CI 0.47 to 14.21, p = 0.04).

Conclusion

Our study established the efficacy of iTBS in improving motor cortical plasticity, motor function, and daily functioning in stroke patients. However, the review requires evidence from additional randomized controlled trials and high-quality research.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/

Sensorimotor performance after high-definition transcranial direct current stimulation over the primary somatosensory or motor cortices in men versus women

The primary somatosensory (S1) cortex is a central structure in motor performance. However, transcranial direct current stimulation (tDCS) research aimed at improving motor performance usually targets the primary motor cortex (M1). Recently, sex was found to mediate tDCS response. Thus, we investigated whether tDCS with an anodal electrode placed over S1 improves motor performance and sensation perception in men versus women. Forty-five participants randomly received 15-min high-definition tDCS (HD-tDCS) at 1 mA to S1, M1, or sham stimulation. Reaching performance was tested before and immediately following stimulation. Two-point orientation discrimination (TPOD) of fingers and proprioception of a reaching movement were also tested. Although motor performance did not differ between groups, reaching reaction time improved in the M1 group men. Reaching movement time and endpoint error improved in women and men, respectively. Correct trials percentage for TPOD task was higher in the S1 compared to the M1 group in the posttest and improved only in the S1 group. Reaching movement time for the proprioception task improved, overall, and endpoint error did not change. Despite the reciprocal connections between S1 and M1, effects of active tDCS over S1 and M1 may specifically influence sensation perception and motor performance, respectively. Also, sex may mediate effects of HD-tDCS on motor performance.

Synaptic plasticity mechanisms behind TMS efficacy: insights from its application to animal models

Neural plasticity is defined as a reshape of communication paths among neurons, expressed through changes in the number and weights of synaptic contacts. During this process, which occurs massively during early brain development but continues also in adulthood, specific brain functions are modified by activity-dependent processes, triggered by external as well as internal stimuli. Since transcranial magnetic stimulation (TMS) produces a non-invasive form of brain cells activation, many different TMS protocols have been developed to treat neurological and psychiatric conditions and proved to be beneficial. Although neural plasticity induction by TMS has been widely assessed on human subjects, we still lack compelling evidence about the actual biological and molecular mechanisms. To support a better comprehension of the involved phenomena, the main focus of this review is to summarize what has been found through the application of TMS to animal models. The hope is that such integrated view will shed light on why and how TMS so effectively works on human subjects, thus supporting a more efficient development of new protocols in the future.

The Modulatory Effects of Intermittent Theta Burst Stimulation in Combination With Mirror Hand Motor Training on Functional Connectivity: A Proof-of-Concept Study

Mirror training (MT) is an observation-based motor learning strategy. Intermittent theta burst stimulation (iTBS) is an accelerated form of excitatory repetitive transcranial magnetic stimulation (rTMS) that has been used to enhance the cortical excitability of the motor cortices. This study aims to investigate the combined effects of iTBS with MT on the resting state functional connectivity at alpha frequency band in healthy adults. Eighteen healthy adults were randomized into one of three groups—Group 1: iTBS plus MT, Group 2: iTBS plus sham MT, and Group 3: sham iTBS plus MT. Participants in Groups 1 and 3 observed the mirror illusion of the moving (right) hand in a plain mirror for four consecutive sessions, one session/day, while participants in Group 2 received the same training with a covered mirror. Real or sham iTBS was applied daily over right motor cortex prior to the training. Resting state electroencephalography (EEG) at baseline and post-training was recorded when participants closed their eyes. The mixed-effects model demonstrated a significant interaction effect in the coherence between FC4 and C4 channels, favoring participants in Group 1 over Group 3 (Δβ = −0.84, p = 0.048). A similar effect was also found in the coherence between FC3 and FC4 channels favoring Group 1 over Group 3 (Δβ = −0.43, p = 0.049). In contrast to sham iTBS combined with MT, iTBS combined with MT may strengthen the functional connectivity between bilateral premotor cortices and ipsilaterally within the motor cortex of the stimulated hemisphere. In contrast to sham MT, real MT, when combined with iTBS, might diminish the connectivity among the contralateral parietal–frontal areas.

Efficacy of coupling intermittent theta-burst stimulation and 1 Hz repetitive transcranial magnetic stimulation to enhance upper limb motor recovery in subacute stroke patients: A randomized controlled trial

BACKGROUND

Both 1 Hz repetitive transcranial magnetic stimulation (rTMS) and intermittent theta-burst stimulation (iTBS) are reported to benefit upper limb motor function rehabilitation in patients with stroke. However, the efficacy of combining 1 Hz rTMS and iTBS has not been adequately explored.

OBJECTIVE

We aimed to compare the effects of 1 Hz rTMS and the combination of 1 Hz rTMS and iTBS on the upper limb motor function in the subacute phase post-stroke.

METHODS

Twenty-eight participants were randomly assigned to three groups: Group A (1 Hz rTMS over the contralesional primary motor cortex (M1) and iTBS over the ipsilesional M1), Group B (contralesional 1 Hz rTMS and ipsilesional sham iTBS), and Group C (contralesional sham 1 Hz rTMS and ipsilesional sham iTBS). The participants received the same conventional rehabilitation accompanied by sessions of transcranial magnetic stimulation for two weeks (5 days one week). Motor-evoked potential (MEP), upper extremity Fugl-Meyer Assessment (UE-FMA), and Barthel Index (BI) were performed before and after the sessions.

RESULTS

Group A showed greater UE-FMA, BI, and MEP amplitude improvement and more significant decrement in MEP latency compared to Group B and Group C in testable patients. Correlation analyses in Group A revealed a close relation between ipsilesional MEP amplitude increment and UE-FMA gain.

CONCLUSIONS

The combining of 1 Hz rTMS and iTBS protocol in the present study is tolerable and more beneficial for motor improvement than the single use of 1 Hz rTMS in patients with subacute stroke.

Noninvasive Brain Stimulation & Space Exploration: Opportunities and Challenges

As NASA prepares for longer space missions aiming for the Moon and Mars, astronauts' health and performance are becoming a central concern due to the threats associated with galactic cosmic radiation, unnatural gravity fields, and life in extreme environments. In space, the human brain undergoes functional and structural changes related to fluid shift and changes in intracranial pressure. Behavioral abnormalities, such as cognitive deficits, sleep disruption, and visuomotor difficulties, as well as psychological effects, are also an issue. We discuss opportunities and challenges of noninvasive brain stimulation (NiBS) methods - including transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES) - to support space exploration in several ways. NiBS includes safe and portable techniques already applied in a wide range of cognitive and motor domains, as well as therapeutically. NiBS could be used to enhance in-flight performance, supporting astronauts during pre-flight Earth-based training, as well as to identify biomarkers of post-flight brain changes for optimization of rehabilitation/compensatory strategies. We review these NiBS techniques and their effects on brain physiology, psychology, and cognition.

Multimodal Sensory-Spatial Integration and Retrieval of Trained Motor Patterns for Body Coordination in Musicians and Dancers

Dancers and musicians are experts in spatial and temporal processing, which allows them to coordinate movement with music. This high-level processing has been associated with structural and functional adaptation of the brain for high performance sensorimotor integration. For these integration processes, adaptation does not only take place in primary and secondary sensory and motor areas but also in tertiary brain areas, such as the lateral prefrontal cortex (lPFC) and the intraparietal sulcus (IPS), providing vital resources for highly specialized performance. Here, we review evidence for the role of these brain areas in multimodal training protocols and integrate these findings into a new model of sensorimotor processing in complex motor learning.

Menstrual Cycle Modulates Motor Learning and Memory Consolidation in Humans

Numerous studies have noted that sex and/or menstrual phase influences cognitive performance (in particular, declarative memory), but the effects on motor learning (ML) and procedural memory/consolidation remain unclear. In order to test the hypothesis that ML differs across menstrual cycle phases, initial ML, overlearning, consolidation, and final performance were assessed in women in the follicular, preovulation and luteal phases. Primary motor cortex (M1) oscillations were assessed neuro-physiologically, and premenstrual syndrome and interoceptive awareness scores were assessed psychologically. We found not only poorer performance gain through initial ML but also lower final performance after overlearning a day and a week later in the luteal group than in the ovulation group. This behavioral difference could be explained by particular premenstrual syndrome symptoms and associated failure of normal M1 excitability in the luteal group. In contrast, the offline effects, i.e., early and late consolidation, did not differ across menstrual cycle phases. These results provide information regarding the best time in which to start learning new sensorimotor skills to achieve expected gains.

Enhancing mirror visual feedback with intermittent theta burst stimulation in healthy adults

BACKGROUND

Excitatory brain stimulation, in the form of intermittent theta burst stimulation (iTBS), combined with mirror visual feedback (MVF), is hypothesized to promote neuroplasticity and motor performance.

OBJECTIVE

This study aimed to investigate the combined effects of iTBS with mirror training (MT) on the MVF-induced sensorimotor event-related desynchronization (ERD) and the non-dominant hand motor performance in healthy adults.

METHODS

Eighteen healthy right-handed subjects were randomly assigned to one of three groups (Group 1: iTBS plus MT, Group 2: iTBS plus sham MT, or Group 3: sham iTBS plus MT). For participants in Groups 1 and 3, motor training was performed for 15 minutes for the right hand over four consecutive days, with MVF superimposing on their inactive left hand behind a mirror. Participants in Group 2 received the same right-hand motor training, but the mirror was covered without MVF. iTBS or sham iTBS was applied daily over the right primary motor cortex prior to the training. Electroencephalography at pre/post-training was recorded while participants performed right-hand movement under mirror and direct view. Motor performance was assessed at baseline and post-training.

RESULTS

Baseline comparisons demonstrated that a shift in sensorimotor ERD towards the right hemisphere was induced by MVF, in mu-1 (8-10 Hz) (p = 0.002), mu-2 (10-12 Hz) (p = 0.004) and beta-1 (12-16 Hz) (p = 0.049) bands. After the training, participants in Group 1 showed a stronger MVF-induced sensorimotor ERD in mu-1 (p = 0.017) and mu-2 (p = 0.009) bands than those in Group 3. No significant between-group difference in motor outcomes was observed.

CONCLUSIONS

iTBS appears to prime subjects' brain to be more receptive to MVF.

Arm Ability Training (AAT) Promotes Dexterity Recovery After a Stroke-a Review of Its Design, Clinical Effectiveness, and the Neurobiology of the Actions

Arm Ability Training (AAT) has been specifically designed to promote manual dexterity recovery for stroke patients who have mild to moderate arm paresis. The motor control problems that these patients suffer from relate to a lack of efficiency in terms of the sensorimotor integration needed for dexterity. Various sensorimotor arm and hand abilities such as speed of selective movements, the capacity to make precise goal-directed arm movements, coordinated visually guided movements, steadiness, and finger dexterity all contribute to our "dexterity" in daily life. All these abilities are deficient in stroke patients who have mild to moderate paresis causing focal disability. The AAT explicitly and repetitively trains all these sensorimotor abilities at the individual's performance limit with eight different tasks; it further implements various task difficulty levels and integrates augmented feedback in the form of intermittent knowledge of results. The evidence from two randomized controlled trials indicates the clinical effectiveness of the AAT with regard to the promotion of "dexterity" recovery and the reduction of focal disability in stroke patients with mild to moderate arm paresis. In addition, the effects have been shown to be superior to time-equivalent "best conventional therapy." Further, studies in healthy subjects showed that the AAT induced substantial sensorimotor learning. The observed learning dynamics indicate that different underlying sensorimotor arm and hand abilities are trained. Capacities strengthened by the training can, in part, be used by both arms. Non-invasive brain stimulation experiments and functional magnetic resonance imaging data documented that at an early stage in the training cortical sensorimotor network areas are involved in learning induced by the AAT, yet differentially for the tasks trained. With prolonged training over 2 to 3 weeks, subcortical structures seem to take over. While behavioral similarities in training responses have been observed in healthy volunteers and patients, training-induced functional re-organization in survivors of a subcortical stroke uniquely involved the ipsilesional premotor cortex as an adaptive recruitment of this secondary motor area. Thus, training-induced plasticity in healthy and brain-damaged subjects are not necessarily the same.

Predicting Training Gain for a 3 Week Period of Arm Ability Training in the Subacute Stage After Stroke

Background: Biomarkers for gains of evidence based interventions for upper limb motor training in the subacute stage following stroke have rarely been described. Information about these parameters might help to identify patients who benefit from specific interventions and to determine individually expected behavioral gains for a certain period of therapy. Objective: To evaluate predictors for hand motor outcome after arm ability training in the subacute stage after stroke selected from known potentially relevant parameters (initial motor strength, structural integrity of the pyramidal tract and functional motor cortex integrity). Methods: We applied the arm ability training (AAT) over 3 weeks to a subpopulation of stroke patients with mild arm paresis, i.e., in 14 patients on average 4 weeks after stroke. The following biomarkers were measured before therapy onset: grip strength on the affected hand, transcranial magnetic stimulation recruitment curve steepness over the primary motor hand area [slope ratio between the ipsilesional hemisphere (IH) and contralesional hemisphere (CH)], and diffusion weighted MRI fractional anisotropy (FA) in the posterior limb of the internal capsule (PLIC; determined as a lateralization index between IH and CH). Outcome was assessed as the AATgain (percentage improvement over training). The "Test d'Evaluation des Membres Supérieurs de Personnes Âgées" (TEMPA) was assessed before and after training to test for possible associations of AAT with activity of daily living. Results: A stepwise linear regression identified the lateralization index of PLIC FA as the only significant predictor for AAT-gain (R ² = 0.519; P = 0.029). AAT-gain was positively associated (r = 0.59; P = 0.028) with improvement in arm function during daily activities (TEMPA). Conclusions: While all mildly affected patients achieved a clinically relevant therapeutic effect, pyramidal tract integrity nevertheless had a modifying role for clinical benefit.