Influence of repetitive transcranial magnetic stimulation on tibialis anterior activity during walking in humans

The Effect of Non-invasive Brain Stimulation on Gait in Healthy Young and Older Adults: A Systematic Review of the Literature

BACKGROUND AND OBJECTIVES

Walking is an important function which requires coordinated activity of sensory-motor neural networks. Noninvasive brain stimulation (NIBS) is a safe neuromodulatory technique with motor function-improving effects. This study aimed to determine the effect of different types of NIBS interventions explored in randomized controlled trials on gait in healthy young and older adults.

METHODS

Based on the PRISMA approach, we conducted an electronic search in PubMed, Web of Science, Scopus, and PEDro for randomized clinical trials assessing the effect of NIBS on gait in healthy young and older adults and performed a narrative review.

RESULTS

Fourteen studies were included in this systematic review. According to the outcomes, transcranial direct current stimulation (tDCS) over the motor cortex and transcranial alternating current stimulation (tACS) over the cerebellum seem to be promising for improving gait characteristics such as speed, synchronization, and variability. Furthermore, tDCS over the dorsolateral prefrontal cortex (DLPFC) improved gait speed and reduced gait parameter variability under dual-task conditions. Only one repetitive transcranial magnetic stimulation was available, which showed no effects. No studies were available for transcranial random noise stimulation, and transcranial pulsed current stimulation. Moreover, the intervention parameters of the included studies were heterogeneous, and studies comparing directly specific intervention protocols were missing.

CONCLUSION

NIBS is a promising approach to improve gait in healthy young and older adults. Anodal tDCS over the motor areas and DLPFC, and tACS over the cerebellum have shown positive effects on gait.

Safety Considerations for Cerebellar Theta Burst Stimulation

PURPOSE

The cerebellum is an intricate neural structure that orchestrates various cognitive and behavioral functions. In recent years, there has been an increasing interest in neuromodulation of the cerebellum with transcranial magnetic stimulation (TMS) for therapeutic and basic science applications. Theta burst stimulation (TBS) is an efficient and powerful TMS protocol that is able to induce longer-lasting effects with shorter stimulation times compared with traditional TMS. Parameters for cerebellar TBS are traditionally framed in the bounds of TBS to the cerebral cortex, even when the 2 have distinct histologic, anatomical, and functional characteristics. Tolerability limits have not been systematically explored in the literature for this specific application. Therefore, we aimed to determine the stimulation parameters that have been used for cerebellar. TBS to date and evaluate adverse events and adverse effects related to stimulation parameters.

METHODS

We used PubMed to perform a critical review of the literature based on a systematic review of original research studies published between September 2008 and November 2019 that reported on cerebellar TBS. We recovered information from these publications and communication with authors about the stimulation parameters used and the occurrence of adverse events.

FINDINGS

We identified 61 research articles on interventions of TBS to the cerebellum. These articles described 3176 active sessions of cerebellar TBS in 1203 individuals, including healthy participants and patients with various neurologic conditions, including brain injuries. Some studies used substantial doses (eg, pulse intensity and number of pulses) in short periods. No serious adverse events were reported. The specific number of patients who experienced adverse events was established for 48 studies. The risk of an adverse event in this population (n = 885) was 4.1%. Adverse events consisted mostly of discomfort attributable to involuntary muscle contractions. Authors used a variety of methods for calculating stimulation dosages, ranging from the long-established reference of electromyography of a hand muscle to techniques that atone for some of the differences between cerebrum and cerebellum.

IMPLICATIONS

No serious adverse events have been reported for cerebellar TBS. There is no substantial evidence of a tolerable maximal-efficacy stimulation dose in humans. There is no assurance of equivalence in the translation of cortical excitability and stimulation intensities from the cerebral cortex to cerebellar regions. Further research for the stimulation dose in cerebellar TBS is warranted, along with consistent report of adverse events. © 2020 Elsevier HS Journals, Inc.

Cortical Oscillations during Gait: Wouldn't Walking be so Automatic?

Gait is often considered as an automatic movement but cortical control seems necessary to adapt gait pattern with environmental constraints. In order to study cortical activity during real locomotion, electroencephalography (EEG) appears to be particularly appropriate. It is now possible to record changes in cortical neural synchronization/desynchronization during gait. Studying gait initiation is also of particular interest because it implies motor and cognitive cortical control to adequately perform a step. Time-frequency analysis enables to study induced changes in EEG activity in different frequency bands. Such analysis reflects cortical activity implied in stabilized gait control but also in more challenging tasks (obstacle crossing, changes in speed, dual tasks…). These spectral patterns are directly influenced by the walking context but, when analyzing gait with a more demanding attentional task, cortical areas other than the sensorimotor cortex (prefrontal, posterior parietal cortex, etc.) seem specifically implied. While the muscular activity of legs and cortical activity are coupled, the precise role of the motor cortex to control the level of muscular contraction according to the gait task remains debated. The decoding of this brain activity is a necessary step to build valid brain-computer interfaces able to generate gait artificially.

Priming With Intermittent Theta Burst Transcranial Magnetic Stimulation Promotes Spinal Plasticity Induced by Peripheral Patterned Electrical Stimulation

This study explored the effect of corticospinal activity on spinal plasticity by examining the interactions between intermittent theta burst transcranial magnetic stimulation (iTBS) of the motor cortex and peripheral patterned electrical stimulation (PES) of the common peroneal nerve (CPN). Healthy volunteers (n = 10) received iTBS to the tibialis anterior (TA) muscle zone of the motor cortex and PES of the CPN in three separate sessions: (1) iTBS-before-PES, (2) iTBS-after-PES, and (3) sham iTBS-before-PES. The PES protocol used 10 100-Hz pulses every 2 s for 20 min. Reciprocal inhibition (RI) from the TA to soleus muscle and motor cortical excitability of the TA and soleus muscles were assessed at baseline, before PES, and 0, 15, 30, and 45 min after PES. When compared to the other protocols, iTBS-before-PES significantly increased changes in disynaptic RI for 15 min and altered long-loop presynaptic inhibition immediately after PES. Moreover, the iTBS-induced cortical excitability changes in the TA before PES were correlated with the enhancement of disynaptic RI immediately after PES. These results demonstrate that spinal plasticity can be modified by altering cortical excitability. This study provides insight into the interactions between modulation of corticospinal excitability and spinal RI, which may help in developing new rehabilitation strategies.