Effects of cerebellar transcranial direct current stimulation on the excitability of spinal motor neurons and vestibulospinal tract in healthy individuals.

Cerebellar transcranial direct current stimulation (ctDCS) modulates cerebellar cortical excitability in a polarity-dependent manner and affects inhibitory pathways from the cerebellum. The cerebellum modulates spinal reflex excitability via the vestibulospinal tract and other pathways projecting to the spinal motor neurons; however, the effects of ctDCS on the excitability of spinal motor neurons and vestibulospinal tract remain unclear. The experiment involved 13 healthy individuals. ctDCS (sham-ctDCS, anodal-ctDCS, and cathodal-ctDCS) was applied to the cerebellar vermis at 2 mA with an interval of at least 3 days between each condition. We measured the maximal M-wave (Mmax) and maximal H-reflex (Hmax) in the right soleus muscle to assess the excitability of spinal motor neurons. We applied galvanic vestibular stimulation (GVS) for 200 ms at 100 ms before tibial nerve stimulation to measure Hmax conditioned by GVS (GVS-Hmax) and calculated the change rate of Hmax by GVS as the excitability of vestibulospinal tract. We measured the Mmax, Hmax, and GVS-Hmax before, during, and after ctDCS in the sitting posture. No main effects of tDCS condition, main effects of time, or interaction effects were observed in Hmax/Mmax or the change rate of Hmax by GVS. It has been suggested that ctDCS does not affect the excitability of spinal motor neurons and vestibulospinal tract, as measured by neurophysiological methods, such as the H-reflex, in healthy individuals in a sitting posture. Effect of ctDCS on other descending pathways to spinal motor neurons, the neurological mechanism of tDCS and the cerebellar activity during the experiment may have contributed to these results. Therefore, we need to investigate the involvement of the cerebellum in Hmax/Mmax and the change rate of Hmax by GVS under different neuromodulation techniques and postural conditions.

Effects of Anodal tDCS Applied Over the Cerebellum Combined with Physical Therapy on Center of Gravity Sway in a Patient with Cerebellar Ataxia: A Single-Case Study.

Damage to the cerebellum results in dysfunctional standing postural control. Patients with cerebellar ataxia have a larger sway in the center of gravity (COG) while standing. Transcranial direct current stimulation (tDCS) has been applied in the rehabilitation of patients with central nervous system disorders; however, its effect on COG sway in patients with cerebellar ataxia remains unknown. We aimed to confirm the effects of anodal cerebellar tDCS (ctDCS) combined with physical therapy on COG sway in a patient with cerebellar ataxia using a retrospective ABA single-case study design. This study involved a patient with left cerebellar hemorrhage. Walking and postural balance rehabilitation were conducted in phase A. Anodal ctDCS was combined with the walking and postural balance rehabilitation in phase B. We measured COG sway in the open- and closed-eyes standing conditions daily throughout all the phases. In the open-eyes standing condition, there was no significant change in COG sway in phase B. Conversely, in the closed-eyes standing condition, the circumferential area, total sway path length, and anteroposterior sway path length decreased in phase B. No change was observed in the mediolateral sway path length. The combination of anodal ctDCS and physical therapy may decrease COG sway in patients with cerebellar ataxia in the closed-eyes standing condition, and its effect may be greater in the anteroposterior direction.

Characteristics of limb kinematics in the gait disorders of post-stroke patients.

Post-stroke gait disorders involve altered lower limb kinematics. Recently, the endpoint of the lower limb has been used as a control variable to understand gait kinematics better. In a cross-sectional study of sixty-seven post-stroke patients, the limb extension angle and effective limb length during gait were used as input variables with a mixed Gaussian model-based probabilistic clustering approach to identify five distinct clusters. Each cluster had unique characteristics related to motor paralysis, spasticity, balance ability, and gait strategy. Cluster 1 exhibited high limb extension angle and length values, indicating increased spasticity. Cluster 2 had moderate extension angles and high limb lengths, indicating increased spasticity and reduced balance ability. Cluster 3 had low limb extension angles and high limb length, indicating reduced balance ability, more severe motor paralysis, and increased spasticity. Cluster 4 demonstrated high extension angles and short limb lengths, with a gait strategy that prioritized stride length in the component of gait speed. Cluster 5 had moderate extension angles and short limb lengths, with a gait strategy that prioritized cadence in the component of gait speed. These findings provide valuable insights into post-stroke gait impairment and can guide the development of personalized and effective rehabilitation strategies.

Effects of Transcranial Direct Current Stimulation of Bilateral Supplementary Motor Area on the Lower Limb Motor Function in a Stroke Patient with Severe Motor Paralysis: A Case Study.

In patients with severe motor paralysis, increasing the excitability of the supplementary motor area (SMA) in the non-injured hemisphere contributes to the recovery of lower limb motor function. However, the contribution of transcranial direct current stimulation (tDCS) over the SMA of the non-injured hemisphere in the recovery of lower limb motor function is unclear. This study aimed to examine the effects of tDCS on bilateral hemispheric SMA combined with assisted gait training. A post-stroke patient with severe motor paralysis participated in a retrospective AB design. Assisted gait training was performed only in period A and tDCS to the SMA of the bilateral hemisphere combined with assisted gait training (bi-tDCS) was performed in period B. Additionally, three conditions were performed for 20 min each in the intervals between the two periods: (1) assisted gait training only, (2) assisted gait training combined with tDCS to the SMA of the injured hemisphere, and (3) bi-tDCS. Measurements were muscle activity and beta-band intermuscular coherence (reflecting corticospinal tract excitability) of the vastus medialis muscle. The bi-tDCS immediately and longitudinally increased muscle activity and intermuscular coherence. We consider that bi-tDCS may be effective in recovering lower limb motor function in a patient with severe motor paralysis.