tDCS combined with optokinetic drift reduces egocentric neglect in severely impaired post-acute patients

Interactions between tDCS treatment and COMT Val158Met in poststroke cognitive impairment

OBJECTIVE

This study aimed to explore the effect of catechol-O-methyltransferase (COMT) Val158Met and brain-derived neurotrophic factor (BDNF) Val66Met to post-stroke cognitive impairment (PSCI) and the interaction with transcranial direct current stimulation (tDCS).

METHODS

Seventy-six patients with PSCI were randomly assigned to Group (1) (n = 38) to receive anodal tDCS of left dorsolateral prefrontal cortex or Group (2) (n = 38) to receive sham stimulation. The intensity of the tDCS was 2 mA, and the stimulations were applied over the left DLPFC for 10 sessions. The Montreal Cognitive Assessment (MoCA) and backward digit span test (BDST) were assessed before, immediately after, and one month after stimulation.

RESULTS

After stimulation, patients in the tDCS group showed better improvement in both MoCA and BDST than those in the sham group. The results of GLMs also supported the main effects of tDCS on general cognitive function and working memory. Then we found that COMT genotype may have a main effect on the improvement of MoCA and BDST, and there may be an interaction between COMT genotype and tDCS in enhancing BDST. In contrast, BDNF genotype showed no significant main or interaction effects on any scales.

CONCLUSIONS

These findings demonstrate that tDCS can improve cognition after stroke. Gene polymorphisms of COMT can affect the efficacy of tDCS on PSCI, but BDNF may not.

SIGNIFICANCE

This study found that COMT Val158Met has an interaction on the efficacy of prefrontal tDCS in cognitive function, which provides reference for future tDCS research and clinical application.

Digital Therapeutics for the Egocentric and Allocentric Neglects in Patients with Brain Injury: A Mini Review

Various therapeutic approaches have been developed for neglect. Many studies have demonstrated the effect of digital therapeutics (DTx) on neglect. However, few studies have reported the effects of DTx on egocentric and allocentric neglect. The differentiation of types of neglect and separate interventions is crucial in the rehabilitation process. In this article, seven studies on DTx on egocentric and allocentric neglect were reviewed. DTx, which was employed in these studies, could be classified as follows: (1) software adaptation in traditional treatment, (2) VR game using the head-mount display as treatment, and (3) the development of a new digital program like ReMoVES. In addition, more studies and more effective results were reported for egocentric neglect than for allocentric neglect. In future studies, each effect on egocentric and allocentric neglect should be identified in detail with the appropriate use of differential evaluation and long-term application of independent DTx.

Innovative Therapy Combining Neck Muscle Vibration and Transcranial Direct Current Stimulation in Association with Conventional Rehabilitation in Left Unilateral Spatial Neglect Patients: HEMISTIM Protocol for a Randomized Controlled Trial

Unilateral spatial neglect (USN) rehabilitation requires the development of new methods that can be easily integrated into conventional practice. The aim of the HEMISTIM protocol is to assess immediate and long-term recovery induced by an innovative association of left-side neck-muscle vibration (NMV) and anodal transcranial Direct Current Stimulation (tDCS) on the ipsilesional posterior parietal cortex during occupational therapy sessions in patients with left USN. Participants will be randomly assigned to four groups: control, Left-NMV, Left-NMV + sham-tDCS or Left-NMV + anodal-tDCS. NMV and tDCS will be applied during the first 15 min of occupational therapy sessions, three days a week for three weeks. USN will be assessed at baseline, just at the end of the first experimental session, after the first and third weeks of the protocol and three weeks after its ending. Our primary outcome will be the evolution of the functional Catherine Bergego Scale score. Secondary outcome measures include five tests that investigate different neuropsychological aspects of USN. Left NMV, by activating multisensory integration neuronal networks, might enhance effects obtained by conventional therapy since post-effects were shown when it was combined with upper limb movements. We expect to reinforce lasting intermodal recalibration through LTP-like plasticity induced by anodal tDCS.

Transcranial direct current stimulation in neglect rehabilitation after stroke: a systematic review

Hemispatial neglect is one of the most frequent attention disorders after stroke. The presence of neglect is associated with longer hospital stays, extended rehabilitation periods, and poorer functional recovery. Transcranial direct current stimulation (tDCS) is a new technique with promising results in neglect rehabilitation; therefore, the objective of this systematic review, performed following the PRISMA guidelines, is to evaluate the effectiveness of tDCS on neglect recovery after stroke. The search was done in MEDLINE (PubMed), Web of Science, Scopus, Cochrane Library, and BioMed Central databases. A total of 311 articles were found; only 11 met the inclusion criteria, including 152 post-stroke patients in total. Methodological quality and risk of bias were assessed for all the studies, and methodological characteristics of the studies, sample sizes, methods, main results, and other relevant data were extracted. tDCS intervention ranged from one to twenty sessions distributed in 1 day to 4 weeks, with intensity ranged from 1 to 2 mA. We found moderate evidence for the efficacy of tDCS in the rehabilitation of hemispatial neglect after a stroke, being more effective in combination with other interventions. Nonetheless, the limited number of studies and some studies' design characteristics makes it risky to draw categorical conclusions. Since scientific evidence is still scarce, further research is needed to determine the advantage of this treatment in acute, sub-acute and chronic stroke patients. Future studies should include larger samples, longer follow-ups, and broader neurophysiological assessments, with the final aim of establishing the appropriate use of tDCS as an adjuvant intervention in neurorehabilitation settings.

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.

Efficacy of Unilateral and Bilateral Parietal Transcranial Direct Current Stimulation on Right Hemispheric Stroke Patients With Neglect Symptoms: A Proof-of-Principle Study

Different transcranial direct current stimulation (tDCS) protocols have been tested to improve visuospatial neglect (VSN). So far, methodological heterogenity limits reliable conclusions about optimal stimualtion set-up. With this proof-of-principle study behavioral effects of two promising (uni- vs. bilateral) stimulation protocols were directly compared to gain more data for an appropriate tDCS protocol in subacute neglect patients. Notably, each tDCS set-up was combined with an identical sham condition to improve comparability. In a double-blind sham-controlled cross-over study 11 subacute post-stroke neglect patients received 20 minutes or 30 seconds (sham) tDCS (2 mA, 0.8 A/m²) parallel to neglect therapy randomized in unilateral (anode-reference: P4-Fp2 10-20 electroencephalography [EEG] system) and bilateral manner (anode-cathode: P4-P3) and 48h wash-out in-between. Before and immediately after stimulation performance were measured in cancellation task (bell test), and line bisection (deviation error). Significant difference between active and assigned sham condition was found in line bisection but not cancellation task. Particularly, deviation error was reduced after bilateral tDCS (hedges g^* = 0.6) compared to bilateral sham, no such advantage were obtained for unilateral stimulation (hedges g^* = 0.2). Using a direct comparison approach findings add further evidence that stimulating both hemispheres (bilateral) is superior in alleviating VSN symptoms than unilateral stimulation in subacute neglect.

Prism Adaptation and Optokinetic Stimulation Comparison in the Rehabilitation of Unilateral Spatial Neglect

Prism adaptation (PA) is one of the most effective treatments for the rehabilitation of unilateral spatial neglect. Optokinetic stimulation (OKS) has also been demonstrated to be effective in ameliorating symptoms of neglect. The aim of this study is to compare the effectiveness of these two methods in a group of neglect patients using a crossover design. A group of 13 post-acute brain-damaged patients with unilateral spatial neglect, who had never been rehabilitated, were treated using PA and OKS. Each treatment was applied for 10 sessions, twice a day, to all patients with both treatments in crossed order (i.e., PA followed by OKS or vice versa). Neuropsychological assessments were performed: before the first (T1), at the end of the first/beginning of the second (T2) and at the end of the second training sessions (T3), and two weeks after the end of treatment (T4). Both procedures produced a significant improvement in clinical tests at T2, independent of the type of training. The results suggest that either PA or OKS induces a significant amelioration of neglect in right brain-damaged patients, mainly in the first block of treatment. Since no differences between treatments were found, they could be applied in clinical practice, according to the requirements of the individual patient.

Exploring the time-course and the reference frames of adaptation to optical prisms and its aftereffects

Prism adaptation (PA) is used to investigate visuo-motor plasticity and to rehabilitate the syndrome of Unilateral Spatial Neglect (USN). After PA, participants show aftereffects (AEs), contralateral to the side of the optical displacement in several tasks. This study explored the features of these AEs, specifically the "egocentric" versus "allocentric, object-based", reference frames involved, and their time course. In three experiments, healthy participants adapted to prismatic lenses inducing a horizontal displacement of the visual field. In Experiment #1, participants adapted to rightward displacing prisms. Four tasks were used requiring repeated pointings towards the participant's subjective egocentric straight-ahead, with the availability of proprioceptive or visual-proprioceptive signals, and, in some conditions, of an external allocentric visual frame (i.e., a rectangular paper sheet). Experiment #2 explored the role of the position of the allocentric frame, with AEs being tested by straight-ahead and frame bisection tasks, requiring pointing toward the external visual frame, placed in different positions of the working space. An egocentric visual proprioceptive task was administered after prism removal and after the execution of the allocentric tasks, to assess the effectiveness of the PA, as indexed by the AEs, and their persistence up to the end of the administration of the allocentric tasks. Experiment #3 differed from #2 in that participants adapted to leftward displacing lenses. Consistent with evidence from USN patients, in Experiment #1, in the egocentric tasks, AEs lasting up to 30 min after PA were found. In Experiment #2, AEs in "allocentric" tasks did not occur, regardless of frame position. Experiment #3 showed AEs in both the "egocentric" and the "allocentric" tasks, with the latter being minor in size. These findings illustrate that the spatial reference systems modulated by PA in extra-personal space primarily operate in spatial "egocentric" reference frames, with a comparatively minor and direction-specific role of "allocentric" frames.

Non-invasive brain stimulation in Stroke patients (NIBS): A prospective randomized open blinded end-point (PROBE) feasibility trial using transcranial direct current stimulation (tDCS) in post-stroke hemispatial neglect

Up to 80% of people who experience a right-hemisphere stroke suffer from hemispatial neglect. This syndrome is debilitating and impedes rehabilitation. We carried out a clinical feasibility trial of transcranial direct current stimulation (tDCS) and a behavioural rehabilitation programme, alone or in combination, in patients with neglect. Patients >4 weeks post right hemisphere stroke were randomized to 10 sessions of tDCS, 10 sessions of a behavioural intervention, combined intervention, or a control task. Primary outcomes were recruitment and retention rates, with secondary outcomes effect sizes on measures of neglect and quality of life, assessed directly after the interventions, and at 6 months follow up. Of 288 confirmed stroke cases referred (representing 7% of confirmed strokes), we randomized 8% (0.6% of stroke cases overall). The largest number of exclusions (91/288 (34%)) were due to medical comorbidities that prevented patients from undergoing 10 intervention sessions. We recruited 24 patients over 29 months, with 87% completing immediate post-intervention and 67% 6 month evaluations. We established poor feasibility of a clinical trial requiring repeated hospital-based tDCS within a UK hospital healthcare setting, either with or without behavioural training, over a sustained time period. Future trials should consider intensity, duration and location of tDCS neglect interventions.Trial registration: ClinicalTrials.gov identifier: NCT02401724.

Can auditory cues improve visuo-spatial neglect? Results of two pilot studies

Although neglect is known to be a multimodal deficit, current interventions often address the visual modality only. Experimental studies, however, found that neglect patients can partially overcome their spatial inattention temporarily when being exposed to auditory cues that move towards the neglected side of space. Two pilot studies investigated the impact of dynamic auditory cueing on egocentric neglect severity in a clinical-therapeutic setting. In both studies, the patient groups received 15 sessions of intervention. Study 1, designed as double-blinded trial with a historical control group, targeted severely impaired early-acute patients who listened to music or audio books which were presented as moving dynamically from right to left. Results showed a reduction in egocentric neglect severity that persisted after therapy termination in the intervention but not in the historical control group. In study 2, based on the comparison with reported effect sizes of previous studies, dynamic meaningful auditory cues and optokinetic stimulation were combined in a computer-based training. Both studies found a significant reduction of neglect severity. Results provide evidence for the reduction of egocentric neglect severity after repetitive auditory cueing therapy in both severely and moderately impaired patients. Our promising findings should be verified thoroughly in randomized-controlled trials.

Transcranial electric stimulation optimizes the balance of visual attention across space

OBJECTIVE

Transcranial direct current stimulation (tDCS) provides a way to modulate spatial attention by enhancing the ratio of neural activity between the left and right hemispheres, with a potential benefit for the rehabilitation of visual neglect.

METHODS

We tested the effect of bilateral tDCS in healthy individuals performing a visual detection task. This protocol consists in the positioning of the anode and cathode on mirror positions over the left and right parietal areas. The stimulation was repeated over three days to maximize the chance to observe a bias to the hemispace controlateral to the anode.

RESULTS

Compared to a sham treatment, left anodal - right cathodal stimulation enhanced attention across the full range of space, since the first day with no build-up effect on the next days, and modified the balance of left-right omissions when stimuli appeared at the same time.

CONCLUSION

Bilateral tDCS improved detection in both visual fields, with no privileged processing of one side, except when concurrent stimuli were presented. The results provide partial support to the hemispheric rivalry hypothesis.

SIGNIFICANCE

The technique has the potential to boost attention in neglect patients but should be used as an adjuvant rather than as an alternative to functional rehabilitation.

Unilateral Spatial Neglect After Stroke: Current Insights

INTRODUCTION

Unilateral spatial neglect (USN) is a disorder of contralesional space awareness which often follows unilateral brain lesion. Since USN impairs awareness of contralesional space/body and often of concomitant motor disorders, its presence represents a negative prognostic factor of functional recovery. Thus, the disorder needs to be carefully diagnosed and treated. Here, we attempted to present a clear and concise picture of current insights in the comprehension and rehabilitation of USN.

METHODS

We first provided an updated overview of USN clinical and neuroanatomical features and then highlighted recent progresses in the diagnosis and rehabilitation of the disease. In relation to USN rehabilitation, we conducted a MEDLINE literature research on three of the most promising interventions for USN rehabilitation: prismatic adaptation (PA), non-invasive brain stimulation (NIBS), and virtual reality (VR). The identified studies were classified according to the strength of their methods.

RESULTS

The last years have witnessed a relative decrement of interest in the study of neuropsychological disorders of spatial awareness in USN, but a relative increase in the study of potential interventions for its rehabilitation. Although optimal protocols still need to be defined, high-quality studies have demonstrated the efficacy of PA, TMS and tDCS interventions for the treatment of USN. In addition, preliminary investigations are suggesting the potentials of GVS and VR approaches for USN rehabilitation.

CONCLUSION

Advancing neuropsychological and neuroscience tools to investigate USN pathophysiology is a necessary step to identify effective rehabilitation treatments and to foster our understanding of neurofunctional bases of spatial cognition in the healthy brain.

Noninvasive Brain Stimulation and Noninvasive Peripheral Stimulation for Neglect Syndrome Following Acquired Brain Injury

OBJECTIVE

Hemispatial neglect is a frequent condition usually following nondominant hemispheric brain injury. It strongly affects rehabilitation strategies and everyday life activities. It is associated with behavioral and cognitive disability with a strong impact on patient's life.

METHODS

We reviewed the published literature on the use of noninvasive brain stimulation, including repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), and of noninvasive peripheral muscle stimulation, as therapeutic strategies for rehabilitation of neglect after acquired brain injury, such as in stroke or in traumatic injuries. The studies were grouped as controlled or uncontrolled studies in each stimulation techniques.

RESULTS

Thirty-four studies were identified and 16 on rTMS, 10 on tDCS, and 8 on vibration. All studies were conducted in adult patients who suffered a stroke, except for one that was conducted in a patient suffering traumatic acquired brain injury and another that was conducted in a patient with brain tumor. In spite of significant variability in treatment protocols, patients' features and assessment of neglect, improvement was reported in almost all studies with no side-effects.

CONCLUSIONS

Noninvasive brain stimulation and neuromuscular vibration are promising therapeutic neuromodulatory approaches for neglect. Further randomized-controlled studies are needed to corroborate their effectiveness as separate and combined techniques.

The Effect of Continuous Theta-Burst Transcranial Magnetic Stimulation Combined with Prism Adaptation on the Neglect Recovery in Stroke Patients

OBJECTIVES

This study was designed to investigate the effect of prism adaptation (PA) combined with continuous theta-burst transcranial magnetic stimulation (cTBS) on the neglect recovery of stroke patients with unilateral neglect.

METHODS

A total of 14 stroke patients with unilateral neglect were randomly assigned to 2 groups including an intervention group undergone PA combined with cTBS over the left intact parietal cortex and a control group. PA combined with sham cTBS was perfomed for 2 weeks in 10 daily sessions. Before and after the intervention, patients were evaluated for visuospatial neglect measured using the Star Cancellation Test (SCT), Line Bisection Task (LBT), Figure Copying Test, and Clock Drawing Task. Neurological function was evaluated using the Modified Rankin Scale (MRS).

RESULTS

Both groups (PA alone and PA+ cTBS) showed improvement in their neglected symptoms (measured by SCT, LBT, Figure Copying Test, and Clock Drawing Task), and in their disability in the neurological function (measured by MRS) (P< .05).

CONCLUSIONS

The results of the present study showed that, transcranial magnetic stimulation did not increase the effect of PA on neglect symptoms in stroke patients.