Stroke rehabilitation using noninvasive cortical stimulation: hemispatial neglect

Using non-invasive transcranial direct current stimulation for neglect and associated attentional deficits following stroke

Neglect is a disabling neuropsychological syndrome that is frequently observed following right-hemispheric stroke. Affected individuals often present with multiple attentional deficits, ranging from reduced orienting towards contralesional space to a generalized impairment in maintaining attention over time. Although a degree of spontaneous recovery occurs in most patients, in some individuals this condition can be treatment-resistant with prominent ongoing non-spatial deficits. Further, there is a large inter-individual variability in response to different therapeutic approaches. Given its potential to alter neuronal excitability and affect neuroplasticity, non-invasive brain stimulation is a promising tool that could potentially be utilized to facilitate recovery. However, there are many outstanding questions regarding its implementation in this heterogeneous patient group. Here we provide a critical overview of the available evidence on the use of non-invasive electrical brain stimulation, focussing on transcranial direct current stimulation (tDCS), to improve neglect and associated attentional deficits after right-hemispheric stroke. At present, there is insufficient robust evidence supporting the clinical use of tDCS to alleviate symptoms of neglect. Future research would benefit from careful study design, enhanced precision of electrical montages, multi-modal approaches exploring predictors of response, tailored dose-control applications and increased efforts to evaluate standalone tDCS versus its incorporation into combination therapy.

Repetitive transcranial magnetic stimulation in stroke rehabilitation: review of the current evidence and pitfalls

Acute brain ischemia causes changes in several neural networks and related cortico-subcortical excitability, both in the affected area and in the apparently spared contralateral hemisphere. The modulation of these processes through modern techniques of noninvasive brain stimulation, namely repetitive transcranial magnetic stimulation (rTMS), has been proposed as a viable intervention that could promote post-stroke clinical recovery and functional independence. This review provides a comprehensive summary of the current evidence from the literature on the efficacy of rTMS applied to different clinical and rehabilitative aspects of stroke patients. A total of 32 meta-analyses published until July 2019 were selected, focusing on the effects on motor function, manual dexterity, walking and balance, spasticity, dysphagia, aphasia, unilateral neglect, depression, and cognitive function after a stroke. Only conventional rTMS protocols were considered in this review, and meta-analyses focusing on theta burst stimulation only were excluded. Overall, both HF-rTMS and LF-rTMS have been shown to be safe and well-tolerated. In addition, the current literature converges on the positive effect of rTMS in the rehabilitation of all clinical manifestations of stroke, except for spasticity and cognitive impairment, where definitive evidence of efficacy cannot be drawn. However, routine use of a specific paradigm of stimulation cannot be recommended yet due to a significant level of heterogeneity of the studies in terms of protocols to be set and outcome measures that have to be used. Future studies need to preliminarily evaluate the most promising protocols before going on to multicenter studies with large cohorts of patients in order to achieve a definitive translation into daily clinical practice.

Repetitive transcranial magnetic stimulation in stroke rehabilitation: review of the current evidence and pitfalls

Acute brain ischemia causes changes in several neural networks and related cortico-subcortical excitability, both in the affected area and in the apparently spared contralateral hemisphere. The modulation of these processes through modern techniques of noninvasive brain stimulation, namely repetitive transcranial magnetic stimulation (rTMS), has been proposed as a viable intervention that could promote post-stroke clinical recovery and functional independence. This review provides a comprehensive summary of the current evidence from the literature on the efficacy of rTMS applied to different clinical and rehabilitative aspects of stroke patients. A total of 32 meta-analyses published until July 2019 were selected, focusing on the effects on motor function, manual dexterity, walking and balance, spasticity, dysphagia, aphasia, unilateral neglect, depression, and cognitive function after a stroke. Only conventional rTMS protocols were considered in this review, and meta-analyses focusing on theta burst stimulation only were excluded. Overall, both HF-rTMS and LF-rTMS have been shown to be safe and well-tolerated. In addition, the current literature converges on the positive effect of rTMS in the rehabilitation of all clinical manifestations of stroke, except for spasticity and cognitive impairment, where definitive evidence of efficacy cannot be drawn. However, routine use of a specific paradigm of stimulation cannot be recommended yet due to a significant level of heterogeneity of the studies in terms of protocols to be set and outcome measures that have to be used. Future studies need to preliminarily evaluate the most promising protocols before going on to multicenter studies with large cohorts of patients in order to achieve a definitive translation into daily clinical practice.

The Effect of Anodal Transcranial Direct Current Stimulation Over Left and Right Temporal Cortex on the Cardiovascular Response: A Comparative Study

Background: Stimulation of the right and left anterior insular cortex, increases and decreases the cardiovascular response respectively, thus indicating the brain’s lateralization of the neural control of circulation. Previous experiments have demonstrated that transcranial direct current stimulation (tDCS) modulates the autonomic cardiovascular control when applied over the temporal cortex. Given the importance of neural control for a normal hemodynamic response, and the potential for the use of tDCS in the treatment of cardiovascular diseases, this study investigated whether tDCS was capable of modulating autonomic regulation.

Methods: Cardiovascular response was monitored during a post-exercise muscle ischemia (PEMI) test, which is well-documented to increase sympathetic drive. A group of 12 healthy participants performed a PEMI test in a control (Control), sham (Sham) and two different experimental sessions where the anodal electrode was applied over the left temporal cortex and right temporal cortex with the cathodal electrode placed over the contralateral supraorbital area. Stimulation lasted 20 min at 2 mA. The hemodynamic profile was measured during a PEMI test. The cardiovascular parameters were continuously measured with a transthoracic bio-impedance device both during the PEMI test and during tDCS.

Results: None of the subjects presented any side effects during or after tDCS stimulation. A consistent cardiovascular response during PEMI test was observed in all conditions. Statistical analysis did not find any significant interaction and any significant main effect of condition on cardiovascular parameters (all ps > 0.316) after tDCS. No statistical differences regarding the hemodynamic responses were found between conditions and time during tDCS stimulation (p > 0.05).

Discussion: This is the first study comparing the cardiovascular response after tDCS stimulation of left and right TC both during exercise and at rest. The results of the current study suggest that anodal tDCS of the left and right TC does not affect functional cardiovascular response during exercise PEMI test and during tDCS. In light of the present and previous findings, the effect of tDCS on the cardiovascular response remains inconclusive.

Imaging effects related to language improvements by rTMS

The functional deficit after a focal brain lesion is determined by the localization and the extent of the tissue damage. Since destroyed tissue usually cannot be replaced in the adult human brain, improvement or recovery of neurological deficits can be achieved only by reactivation of functionally disturbed but morphologically preserved areas or by recruitment of alternative pathways within the functional network. The visualization of disturbed interaction in functional networks and of their reorganization in the recovery after focal brain damage is the domain of functional imaging modalities such as positron emission tomography (PET). Longitudinal assessments at rest and during activation tasks during the early and later periods following a stroke can demonstrate recruitment and compensatory mechanisms in the functional network responsible for complete or partial recovery of disturbed functions. Imaging studies have shown that improvements after focal cortical injury are represented over larger cortical territories. It has also been shown that the unaffected hemisphere in some instances actually inhibits the recovery of ipsilateral functional networks and this effect of transcallosal inhibition can be reduced by non-invasive brain stimutation. Non-invasive brain stimulation (NIBS) can modulate the excitability and activity of targeted cortical regions and thereby alter the interaction within pathologically affected functional networks; this kind of intervention might promote the adaptive cortical reorganization of functional networks after stroke. In poststroke aphasia several studies attempted to restore perilesional neuronal activity in the injured left inferior frontal gyrus by applying excitatory high frequency repetitive transcranial magnetic stimulation (rTMS) or intermittent theta burst stimulation (iTBS) or anodal transcranial direct current stimulation (tDCS), but most NIBS studies in poststroke aphasia employed inhibitory low frequency rTMS for stimulation of the contralesional pars triangularis of the right inferior frontal gyrus (BA 45) in order to reduce right hemisphere hyperactivity and transcallosal inhibition on the left Broca's area. While most studies reported single cases or small case series with chronic poststroke aphasia without any control condition, only a few controlled studies including sham stimulation were performed in chronic stage after stroke. In one controlled randomized study changes in PET activation pattern in the subacute course were related to the clinical improvement. In this "proof-of-principle" study the shift of the activation pattern to the dominant hemisphere induced by inhibitory rTMS over the right inferior frontal gyrus could be demonstrated in the PET activation studies and correlated to improved performance in aphasia tests. NIBS might be a treatment strategy which could improve the effect of other rehabilitative efforts.

Low-frequency rTMS of the unaffected hemisphere in stroke patients: A systematic review

The aim of this review was to summarize the evidence for the effectiveness of low-frequency (LF) repetitive transcranial magnetic stimulation (rTMS) over the unaffected hemisphere in promoting functional recovery after stroke. We performed a systematic search of the studies using LF-rTMS over the contralesional hemisphere in stroke patients and reviewed the 67 identified articles. The studies have been gathered together according to the time interval that had elapsed between the stroke onset and the beginning of the rTMS treatment. Inhibitory rTMS of the contralesional hemisphere can induce beneficial effects on stroke patients with motor impairment, spasticity, aphasia, hemispatial neglect and dysphagia, but the therapeutic clinical significance is unclear. We observed considerable heterogeneity across studies in the stimulation protocols. The use of different patient populations, regardless of lesion site and stroke aetiology, different stimulation parameters and outcome measures means that the studies are not readily comparable, and estimating real effectiveness or reproducibility is very difficult. It seems that careful experimental design is needed and it should consider patient selection aspects, rTMS parameters and clinical assessment tools. Consecutive sessions of rTMS, as well as the combination with conventional rehabilitation therapy, may increase the magnitude and duration of the beneficial effects. In an increasing number of studies, the patients have been enrolled early after stroke. The prolonged follow-up in these patients suggests that the effects of contralesional LF-rTMS can be long-lasting. However, physiological evidence indicating increased synaptic plasticity, and thus, a more favourable outcome, in the early enrolled patients, is still lacking. Carefully designed clinical trials designed are required to address this question. LF rTMS over unaffected hemisphere may have therapeutic utility, but the evidence is still preliminary and the findings need to be confirmed in further randomized controlled trials.

a-tDCS on the ipsilesional parietal cortex boosts the effects of prism adaptation treatment in neglect

BACKGROUND AND OBJECTIVE

The aim of the study is to compare the effects of multiple sessions of cathodal (c-tDCS) or anodal tDCS (a-tDCS) in modulating the beneficial effects of prism adaptation (PA) treatment in neglect patients.

METHODS

30 neglect patients were submitted to 10 daily sessions of PA treatment. Patients were pseudo-randomly divided into 3 groups. In the c-tDCS-group, each PA session was coupled with 20 minutes of cathodal stimulation of the left, intact PPC; in the a-tDCS-group, anodal stimulation was applied to PPC of the damaged hemisphere; in the Sham group, sham stimulation was applied. Neglect was evaluated before and after treatment with the Behavioral Inattention Test.

RESULTS

Combined tDCS-PA treatment induced stronger neglect improvement in the a-tDCSgroup as compared to the Sham group. No improvement was found in the c-tDCS group, with respect to that normally induced by PA and found in the Sham group.

CONCLUSIONS

c-tDCS abolished neglect amelioration after PA, possibly because stimulation affected the sensorimotor network controlling prism adaptation. Instead, a-tDCS PPC boosted neglect amelioration after PA probably thanks to increased excitability of residual tissue in the lesioned hemisphere, which in turn might reduce dysfunctional over-excitability of the intact hemisphere.

Opportunities for Guided Multichannel Non-invasive Transcranial Current Stimulation in Poststroke Rehabilitation

Stroke is a leading cause of serious long-term disability worldwide. Functional outcome depends on stroke location, severity, and early intervention. Conventional rehabilitation strategies have limited effectiveness, and new treatments still fail to keep pace, in part due to a lack of understanding of the different stages in brain recovery and the vast heterogeneity in the poststroke population. Innovative methodologies for restorative neurorehabilitation are required to reduce long-term disability and socioeconomic burden. Neuroplasticity is involved in poststroke functional disturbances and also during rehabilitation. Tackling poststroke neuroplasticity by non-invasive brain stimulation is regarded as promising, but efficacy might be limited because of rather uniform application across patients despite individual heterogeneity of lesions, symptoms, and other factors. Transcranial direct current stimulation (tDCS) induces and modulates neuroplasticity, and has been shown to be able to improve motor and cognitive functions. tDCS is suited to improve poststroke rehabilitation outcomes, but effect sizes are often moderate and suffer from variability. Indeed, the location, extent, and pattern of functional network connectivity disruption should be considered when determining the optimal location sites for tDCS therapies. Here, we present potential opportunities for neuroimaging-guided tDCS-based rehabilitation strategies after stroke that could be personalized. We introduce innovative multimodal intervention protocols based on multichannel tDCS montages, neuroimaging methods, and real-time closed-loop systems to guide therapy. This might help to overcome current treatment limitations in poststroke rehabilitation and increase our general understanding of adaptive neuroplasticity leading to neural reorganization after stroke.

The effect of transcranial direct current stimulation of the motor cortex on exercise-induced pain

PURPOSE

Transcranial direct current stimulation (tDCS) provides a new exciting means to investigate the role of the brain during exercise. However, this technique is not widely used in exercise science, with little known regarding effective electrode montages. This study investigated whether tDCS of the motor cortex (M1) would elicit an analgesic response to exercise-induced pain (EIP).

METHODS

Nine participants completed a VO2max test and three time to exhaustion (TTE) tasks on separate days following either 10 min 2 mA tDCS of the M1, a sham or a control. Additionally, seven participants completed 3 cold pressor tests (CPT) following the same experimental conditions (tDCS, SHAM, CON). Using a well-established tDCS protocol, tDCS was delivered by placing the anodal electrode above the left M1 with the cathodal electrode above dorsolateral right prefrontal cortex. Gas exchange, blood lactate, EIP and ratings of perceived exertion (RPE) were monitored during the TTE test. Perceived pain was recorded during the CPT.

RESULTS

During the TTE, no significant differences in time to exhaustion, RPE or EIP were found between conditions. However, during the CPT, perceived pain was significantly (P < 0.05) reduced in the tDCS condition (7.4 ± 1.2) compared with both the CON (8.6 ± 1.0) and SHAM (8.4 ± 1.3) conditions.

CONCLUSION

These findings demonstrate that stimulation of the M1 using tDCS does not induce analgesia during exercise, suggesting that the processing of pain produced via classic measures of experimental pain (i.e., a CPT) is different to that of EIP. These results provide important methodological advancement in developing the use of tDCS in exercise.

Individualized treatment with transcranial direct current stimulation in patients with chronic non-fluent aphasia due to stroke

While evidence suggests that transcranial direct current stimulation (tDCS) may facilitate language recovery in chronic post-stroke aphasia, individual variability in patient response to different patterns of stimulation remains largely unexplored. We sought to characterize this variability among chronic aphasic individuals, and to explore whether repeated stimulation with an individualized optimal montage could lead to persistent reduction of aphasia severity. In a two-phase study, we first stimulated patients with four active montages (left hemispheric anode or cathode; right hemispheric anode or cathode) and one sham montage (Phase 1). We examined changes in picture naming ability to address (1) variability in response to different montages among our patients, and (2) whether individual patients responded optimally to at least one montage. During Phase 2, subjects who responded in Phase 1 were randomized to receive either real-tDCS or to receive sham stimulation (10 days); patients who were randomized to receive sham stimulation first were then crossed over to receive real-tDCS (10 days). In both phases, 2 mA tDCS was administered for 20 min per real-tDCS sessions and patients performed a picture naming task during stimulation. Patients' language ability was re-tested after 2-weeks and 2-months following real and sham tDCS in Phase 2. In Phase 1, despite considerable individual variability, the greatest average improvement was observed after left-cathodal stimulation. Seven out of 12 subjects responded optimally to at least one montage as demonstrated by transient improvement in picture-naming. In Phase 2, aphasia severity improved at 2-weeks and 2-months following real-tDCS but not sham. Despite individual variability with respect to optimal tDCS approach, certain montages result in consistent transient improvement in persons with chronic post-stroke aphasia. This preliminary study supports the notion that individualized tDCS treatment may enhance aphasia recovery in a persistent manner.

Evidence-based guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS)

A group of European experts was commissioned to establish guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS) from evidence published up until March 2014, regarding pain, movement disorders, stroke, amyotrophic lateral sclerosis, multiple sclerosis, epilepsy, consciousness disorders, tinnitus, depression, anxiety disorders, obsessive-compulsive disorder, schizophrenia, craving/addiction, and conversion. Despite unavoidable inhomogeneities, there is a sufficient body of evidence to accept with level A (definite efficacy) the analgesic effect of high-frequency (HF) rTMS of the primary motor cortex (M1) contralateral to the pain and the antidepressant effect of HF-rTMS of the left dorsolateral prefrontal cortex (DLPFC). A Level B recommendation (probable efficacy) is proposed for the antidepressant effect of low-frequency (LF) rTMS of the right DLPFC, HF-rTMS of the left DLPFC for the negative symptoms of schizophrenia, and LF-rTMS of contralesional M1 in chronic motor stroke. The effects of rTMS in a number of indications reach level C (possible efficacy), including LF-rTMS of the left temporoparietal cortex in tinnitus and auditory hallucinations. It remains to determine how to optimize rTMS protocols and techniques to give them relevance in routine clinical practice. In addition, professionals carrying out rTMS protocols should undergo rigorous training to ensure the quality of the technical realization, guarantee the proper care of patients, and maximize the chances of success. Under these conditions, the therapeutic use of rTMS should be able to develop in the coming years.

Dual-Hemisphere Repetitive Transcranial Magnetic Stimulation for Rehabilitation of Poststroke Aphasia

Background. Recent neuroimaging studies on poststroke aphasia revealed maladaptive cortical changes in both hemispheres, yet their functional contribution in language recovery remains elusive. The aim of this study was to evaluate the long-term efficacy of dual-hemisphere repetitive transcranial magnetic stimulation (rTMS) on poststroke aphasia. Methods. Thirty patients with subacute poststroke nonfluent aphasia were randomly allocated to receive real or sham rTMS. Each patient received 1000 rTMS pulses (1 Hz at 110% of resting motor threshold [rMT] over the right unaffected Broca’s area and 1000 pulses (20 Hz at 80% rMT) over the left affected Broca’s area for 10 consecutive days followed by speech/language training. The language section of the Hemispheric Stroke Scale (HSS), the Stroke Aphasic Depression Questionnaire–Hospital Version (SADQ-H), and the National Institutes of Health Stroke Scale (NIHSS) were measured before, immediately after the 10 sessions, and 1 and 2 months after the last session. Results. At baseline, there were no significant differences between groups in demographic and clinical rating scales. However, there was a significantly greater improvement in the HSS language score as well as in the SADQ-H after real rTMS compared with sham rTMS, which remained significant 2 months after the end of the treatment sessions. Conclusion. This is the first clinical study of dual-hemisphere rTMS in poststroke aphasia. Combining dual-hemisphere rTMS with language training might be a feasible treatment for nonfluent aphasia; further multicenter studies are needed to confirm this result.

Non-invasive brain stimulation in neglect rehabilitation: an update

Here, we review the effects of non-invasive brain stimulation such as transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) in the rehabilitation of neglect. We found 12 studies including 172 patients (10 TMS studies and 2 tDCS studies) fulfilling our search criteria. Activity of daily living measures such as the Barthel Index or, more specifically for neglect, the Catherine Bergego Scale were the outcome measure in three studies. Five studies were randomized controlled trials with a follow-up time after intervention of up to 6 weeks. One TMS study fulfilled criteria for Class I and one for Class III evidence. The studies are heterogeneous concerning their methodology, outcome measures, and stimulation parameters making firm comparisons and conclusions difficult. Overall, there are however promising results for theta-burst stimulation, suggesting that TMS is a powerful add-on therapy in the rehabilitation of neglect patients.