Stimulus Intensity Affects Variability of Motor Evoked Responses of the Non-Paretic, but Not Paretic Tibialis Anterior Muscle in Stroke

Background: Transcranial magnetic stimulus induced motor evoked potentials (MEPs) are quantified either with a single suprathreshold stimulus or using a stimulus response curve. Here, we explored variability in MEPs influenced by different stimulus intensities for the tibialis anterior muscle in stroke. Methods: MEPs for the paretic and non-paretic tibialis anterior (TA) muscle representations were collected from 26 participants with stroke at seven intensities. Variability of MEP parameters was examined with coefficients of variation (CV). Results: CV for the non-paretic TA MEP amplitude and area was significantly lower at 130% and 140% active motor threshold (AMT). CV for the paretic TA MEP amplitude and area did not vary with intensity. CV of MEP latency decreased with higher intensities for both muscles. CV of the silent period decreased with higher intensity for the non-paretic TA, but was in reverse for the paretic TA. Conclusion: We recommend a stimulus intensity of greater than 130% AMT to reduce variability for the non-paretic TA. The stimulus intensity did not affect the MEP variability of the paretic TA. Variability of MEPs is affected by intensity and side tested (paretic and non-paretic), suggesting careful selection of experimental parameters for testing

Understanding the Neural Effects of Non-invasive Brain Stimulation enhanced Aerobic Exercise in Stroke

Background: Cortical priming is a promising adjuvant to conventional rehabilitation that can be used to facilitate neuroplasticity and improve behavioral outcomes. Acute aerobic exercise (AE) and transcranial direct current stimulation (tDCS) are priming tools that have shown individual effects on corticomotor excitability and motor skill learning in healthy individuals and stroke. Although the utility of tDCS has been demonstrated in combination with other motor tasks, the neurophysiological effects of a combination of acute aerobic exercise and tDCS on the lower limb M1 are unknown. Here, we sought to investigate the effects of a combination of aerobic exercise and tDCS on corticomotor excitability, intracortical and transcallosal inhibition and motor function for the lower limb in stroke. Methods: In this cross over study individals with stroke underwent imental sessions i.e. aerobic exercise training (AE) + tDCS, AE and tDCS-only conditions. The exercise conditions included moderate intensity (50 – 65% of heart rate maximum) exercise on a recumbent stepper (25 minutes total, 5 minutes warm up and cool down). Anodal tDCS was administered to the lesioned lower limb M1. Electromyography data was obtained from bilateral tibialis anterior muscles in response to single pulse and paired pulse transcranial magnetic stimulation (TMS). Outcomes included TMS measures of area under the recruitment curve (AURC) recorded from intensities corresponding to 80% – 140% active motor threshold, short interval intracortical inhibition (SICI), ipsilateral silent period (iSP) (an index of transcallosal inhibition (TCI)) and reaction time before and after each condition. SICI and TCI were also measured 30 minutes after each condition. Results: Three individuals withdrew from the study due to personal reasons. Corticomotor excitability (AURC) for the lesioned M1 showed a significant increase for the AE + tDCS and tDCS conditions compared to the AE condition. There were no differences between the AE + tDCS and tDCS conditions. There were no significant differences for the non-lesioned M1. There were no statistically significant differences in SICI, iSP measures and reaction time between all three conditions. Conclusions: Our findings suggest that a single session of exercise and tDCS may increase excitability of the lesioned hemisphere, however these effects were specific to the descending corticomotor pathways. There were no alterations in excitability of the inter-hemispheric and intracortical circuits. Moreover, exercise and tDCS did not affect ankle motor control. Our protocol suggests that a combination of exercise and tDCS may be promising for stroke rehabilitation, but further work is required to validate our findings in a larger cohort

Recumbent stepping aerobic exercise in amyotrophic lateral sclerosis: a pilot study.

Objectives Aerobic exercise can promote neuroplastic responses in the healthy and injured brain. Although the role of exercise in amyotrophic lateral sclerosis (ALS) is debated, new evidence suggests that exercise may reduce disease progression. While common exercise modalities such as the treadmill and cycle ergometer have been explored in ALS, the safety and feasibility of a total body recumbent stepper have not been investigated. Additionally, the functional and neurophysiological effects of recumbent stepping in ALS are still unknown. Here, we investigated the safety and feasibility of a 4-week recumbent stepping program to slow disease progression in ALS and possibly facilitate neuroplasticity. Method Nine individuals with ALS performed moderate intensity recumbent stepping for four weeks. Outcomes included participation satisfaction questionnaire, ALS Functional Rating Scale Revised (ALSFRS-R), clinical tests of walking and endurance, fatigue severity scale, Beck depression inventory, SF-12, and transcranial magnetic stimulation-induced motor evoked potentials (MEPs). All measurements were collected at baseline, post-intervention, and at the 1-month follow-up. Results Eight participants completed the study without any adverse events. The ALSFRS-R scores were similar at the end of the study and at follow-up. No significant differences were noted for any of the clinical outcomes. MEPs were present only in two participants and changes in corticomotor excitability after exercise were minimal. Conclusions Results from this preliminary study support the safety and feasibility of 12 sessions of total body recumbent stepping in individuals with ALS

Safety and Feasibility of Transcranial Direct Current Stimulation in Amyotrophic Lateral Sclerosis – A pilot study with a single subject experimental design.

Introduction: Transcranial direct current stimulation (tDCS) has been explored as a neuromodulatory tool to prime motor function in several neurological disorders. Studies using tDCS in amyotrophic lateral sclerosis (ALS) are limited. We investigated the safety, feasibility and effects of long term tDCS in an individual with ALS. Methods: A 36 year old male diagnosed with clinically definite ALS received twelve sessions each of anodal, sham and cathodal tDCS. Outcome measures included disease progression (revised ALS functional rating scale (ALSFRS-R)), clinical measures of endurance and mobility, and corticomotor excitability. Results: No adverse events or change in disease progression were noticed during the study. Small improvement in gait speed (15% increase) was noticed with anodal tDCS only. Conclusions: This case study demonstrates the safety and feasibility of long term facilitatory and inhibitory tDCS on a single participant with ALS. This study serves as a guideline for implementing tDCS in future ALS trials