Posts Tagged cortical excitability

[ARTICLE] Null Effects on Working Memory and Verbal Fluency Tasks When Applying Anodal tDCS to the Inferior Frontal Gyrus of Healthy Participants – Full Text

Transcranial direct current stimulation (tDCS) is a technique used to modify cognition by modulating underlying cortical excitability via weak electric current applied through the scalp. Although many studies have reported positive effects with tDCS, a number of recent studies highlight that tDCS effects can be small and difficult to reproduce. This is especially the case when attempting to modulate performance using single applications of tDCS in healthy participants. Possible reasons may be that optimal stimulation parameters have yet to be identified, and that individual variation in cortical activity and/or level of ability confound outcomes. To address these points, we carried out a series of experiments in which we attempted to modulate performance in fluency and working memory probe tasks using stimulation parameters which have been associated with positive outcomes: we targeted the left inferior frontal gyrus (LIFG) and compared performance when applying a 1.5 mA anodal current for 25 min and with sham stimulation. There is evidence that LIFG plays a role in these tasks and previous studies have found positive effects of stimulation. We also compared our experimental group (N = 19–20) with a control group receiving no stimulation (n = 24). More importantly, we also considered effects on subgroups subdivided according to memory span as well as to more direct measures of executive function abilities and motivational levels. We found no systematic effect of stimulation. Our findings are in line with a growing body of evidence that tDCS produces unreliable effects. We acknowledge that our findings speak to the conditions we investigated, and that alternative protocols (e.g., multiple sessions, clinical samples, and different stimulation polarities) may be more effective. We encourage further research to explore optimal conditions for tDCS efficacy, given the potential benefits that this technique poses for understanding and enhancing cognition.

Introduction

Transcranial direct current stimulation (or tDCS) is a non-invasive form of brain stimulation which is used to modulate cognitive performance by applying a weak electric current via electrodes placed on the scalp. Early studies measuring effects of tDCS on motor cortical excitability suggested that the applied current can cause directional changes in the resting membrane potentials underneath the electrodes—with predominant depolarization under the anode (known as anodal tDCS) vs. hyperpolarization under the cathode (cathodal tDCS; de Berker et al., 2013). It is widely assumed that effects on cortical excitability map on to cognitive effects, with anodal vs. cathodal tDCS improving vs. worsening the cognitive function of targeted brains regions. However, though widely assumed, this might not necessarily be the case. Current flows between the electrodes with complex effects that are poorly understood. Moreover, an important confounding factor modulating the impact of tDCS may be individual variation in cortical activity and/or level of ability (for reviews, see Miniussi et al., 2013Horvath et al., 2015Li et al., 2015Westwood and Romani, 2017Westwood et al., 2017). These are widely cited as explanations for a number of recent reports of negative, inconsistent, and/or small effects linked to single applications of tDCS especially in healthy participants (see Horvath et al., 2015Mancuso et al., 2016Westwood et al., 2017). Our study will contribute to clarify the scope of tDCS effects by considering tasks that tax executive selection abilities, mediated by the frontal lobes, and where positive, but inconsistent, effects have been reported before. We will consider effects on the whole participant group, but crucially also on subgroups subdivided according to (a) general performance and control abilities; (b) working memory span; and (c) motivation levels to see whether these variables affect tDCS outcomes.[…]

 

Continue —> Frontiers | Null Effects on Working Memory and Verbal Fluency Tasks When Applying Anodal tDCS to the Inferior Frontal Gyrus of Healthy Participants | Neuroscience

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[Abstract] Importance and Difficulties of Pursuing rTMS Research in Acute Stroke

Abstract

Although much research has been done on repetitive transcranial magnetic stimulation (rTMS) in chronic stroke, only sparse research has been done in acute stroke despite the particularly rich potential for neuroplasticity in this stage.

We attempted a preliminary clinical trial in one active, high-quality inpatient rehabilitation facility (IRF) in the U.S. But after enrolling only four patients in the grant period, the study was stopped because of low enrollment.

The purpose of this paper is to offer a perspective describing the important physiologic rationale for including rTMS in the early phase of stroke, the reasons for our poor patient enrollment in our attempted study, and recommendations to help future studies succeed.

We conclude that, if scientists and clinicians hope to enhance stroke outcomes, more attention must be directed to leveraging conventional rehabilitation with neuromodulation in the acute phase of stroke when the capacity for neuroplasticity is optimal. Difficulties with patient enrollment must be addressed by reassessing traditional inclusion and exclusion criteria. Factors that shorten patients’ length of stay in the IRF must also be reassessed at all policy-making levels to make ethical decisions that promote higher functional outcomes while retaining cost consciousness.

Source: Importance and Difficulties of Pursuing rTMS Research in Acute Stroke | Physical Therapy | Oxford Academic

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[ARTICLE] Repetitive transcranial magnetic stimulation and transcranial direct current stimulation in motor rehabilitation after stroke: An update

Abstract

Stroke is a leading cause of adult motor disability. The number of stroke survivors is increasing in industrialized countries, and despite available treatments used in rehabilitation, the recovery of motor functions after stroke is often incomplete.

Studies in the 1980s showed that non-invasive brain stimulation (mainly repetitive transcranial magnetic stimulation [rTMS] and transcranial direct current stimulation [tDCS]) could modulate cortical excitability and induce plasticity in healthy humans.  These findings have opened the way to the therapeutic use of the 2 techniques for stroke. The mechanisms underlying the cortical effect of rTMS and tDCS differ.

This paper summarizes data obtained in healthy subjects and gives a general review of the use of rTMS and tDCS in stroke patients with altered motor functions. From 1988 to 2012, approximately 1400 publications were devoted to the study of non-invasive brain stimulation in humans. However, for stroke patients with limb motor deficit, only 141 publications have been devoted to the effects of rTMS and 132 to those of tDCS. The Cochrane review devoted to the effects of rTMS found 19 randomized controlled trials involving 588 patients, and that devoted to tDCS found 18 randomized controlled trials involving 450 patients.

Without doubt, rTMS and tDCS contribute to physiological and pathophysiological studies in motor control. However, despite the increasing number of studies devoted to the possible therapeutic use of non-invasive brain stimulation to improve motor recovery after stroke, further studies will be necessary to specify their use in rehabilitation.

via Repetitive transcranial magnetic stimulation and transcranial direct current stimulation in motor rehabilitation after stroke: An update.

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[ARTICLE] Enhancement of cortical excitability and lower limb motor function in patients with stroke by transcranial direct current stimulation

Highlights

  1. We evaluate the effect of anodal tDCS for improving motor impairment after stroke.
  2. We recruited 24 patients (tDCS and sham group) with early-stage stroke.
  3. The MEPs became shorter in latency and higher in amplitude in the tDCS group.
  4. Improvements in MI-LE were greater in the tDCS group.
  5. Anodal tDCS is beneficial for improving motor function in the lower limbs.

Abstract

Background: Motor dysfunction in the lower limbs is a common sequela in stroke patients.

Objective: We used transcranial magnetic stimulation (TMS) to determine if applying transcranial direct current stimulation (tDCS) to the primary motor cortex helps enhance cortical excitability. Furthermore, we evaluate if combination anodal tDCS and conventional physical therapy improves motor function in the lower limbs.

Methods

Twenty-four patients with early-stage stroke were randomly assigned to 2 groups: 1) the tDCS group, in which patients received 10 sessions of anodal tDCS and conventional physical therapy; and 2) the sham group, in which patients received 10 sessions of sham stimulation and conventional physical therapy. One day before and after intervention, the motor-evoked potential (MEP) of the affected tibialis anterior muscle was evaluated and motor function was assessed using the lower limb subscale of the Fugl-Meyer Assessment (FMA-LE), lower limb Motricity Index (MI-LE), Functional Ambulatory Category (FAC), Berg Balance Scale (BBS), and gait analysis.

Results: The MEPs in the tDCS group became shorter in latency and higher in amplitude after intervention in comparison with the sham group. Improvements in FMA-LE and MI-LE were greater in the tDCS group, but no significant differences in FAC or BBS scores were found. Also, the changes observed on the gait analyses did not significantly differ between the tDCS and sham groups.

Conclusion: Combination anodal tDCS and conservative physical therapy appears to be a beneficial therapeutic modality for improving motor function in the lower limbs in patients with subacute stroke.

via Enhancement of cortical excitability and lower limb motor function in patients with stroke by transcranial direct current stimulation.

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[WEB SITE] New App Helps Veterans Recover From Brain Injuries

“Constant Therapy,” developed at Boston University, is the latest tool to try to treat patients with traumatic brain injury.

It may look like a child’s memory game or the next addictive iPad app, but the brain games presented on “Constant Therapy” are much more than they appear.

The app, developed at Boston University, is the latest tool to try to treat patients with traumatic brain injury.

“Constant Therapy provides a mobile solution that is cloud-based that allows people to improve their brain function and learning after an event such as a stroke or a traumatic brain injury,” said CEO Veera Anantha…

via New App Helps Veterans Recover From Brain Injuries | NECN.

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[ARTICLE] Neurorehabilitation and Neural Repair

Abstract

Background. Motor deficits after a stroke are thought to be compounded by the development of asymmetric interhemispheric inhibition. Bilateral priming was developed to rebalance this asymmetry and thus improve therapy efficacy.

Objective. This study investigated the effect of bilateral priming before Wii-based Movement Therapy to improve rehabilitation after stroke.

Methods. Ten patients who had suffered a stroke (age, 23-77 years; 3-123 months after stroke) underwent a 14-day program of Wii-based Movement Therapy for upper limb rehabilitation. Formal Wii-based Movement Therapy sessions were immediately preceded by 15 minutes of bilateral priming, whereby active flexion-extension of the less affected wrist drove mirror-symmetric passive movements of the more affected wrist through a custom device. Functional movement was assessed at weeks 0 (before therapy), 3 (after therapy), and 28 (follow-up) using the Wolf Motor Function Test (WMFT), upper limb Fugl-Meyer Assessment (FMA), upper limb range of motion, and Motor Activity Log (MAL). Case-matched controls were patients who had suffered a stroke who received Wii-based Movement Therapy but not bilateral priming.

Results. Upper limb functional ability improved for both groups on all measures tested. Posttherapy improvement on the FMA for primed patients was twice that of the unprimed patients (37.3% vs 14.6%, respectively) and was significantly better maintained at 28 weeks (P = .02). Improvements on the WMFT and MAL were similar for both groups, but the pattern of change in range of motion was strikingly different.

Conclusions. Bilateral priming before Wii-based Movement Therapy led to a greater magnitude and retention of improvement compared to control, especially measured with the FMA. These data suggest that bilateral priming can enhance the efficacy of Wii-based Movement Therapy, particularly for patients with low motor function after a stroke.

via Neurorehabilitation and Neural Repair.

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