Abstract
Reaching ability of the paretic upper extremity in individuals with stroke decreases with increased shoulder abduction (SABD) loads. Transcranial direct current stimulation (tDCS) has been implemented to improve movement ability following stroke. However, results from previous studies vary, perhaps due to the influence of impairment level and the type of motor tasks that were used to study the effects of tDCS. This study specifically examines the impact of SABD loading on the effects of tDCS in 9 individuals with moderate to severe chronic stroke. In 3 different sessions, participants repeated a reaching assessment with various SABD loads (supported on a haptic table, 25%, and 50% of maximum voluntary SABD torque) in random order, pre and post one of the following 15-min tDCS protocols: anodal stimulation of lesioned M1, cathodal stimulation of non-lesioned M1, or anodal stimulation of non-lesioned M1. Sham stimulation was also conducted preceding one of the tDCS sessions. The averaged maximum reaching distance over valid trials was calculated for each condition. We observed significant interactions between SABD load, tDCS protocol and time (i.e., pre or post-tDCS). Post hoc test showed that anodal stimulation of the lesioned M1 caused a clear trend (p = 0.058) of increasing the reaching ability at a medium level of SABD loading (25%), but not for higher loads (50%). This suggests that anodal stimulation increases residual corticospinal tract activity, which successfully increases reaching ability at moderate loads; however, is insufficient to make significant changes at higher SABD loads. We also found that cathodal stimulation of the non-lesioned M1 significantly (p = 0.018) decreased the reaching distance at a high level of SABD loading (50%). This study demonstrated, for the first time, that the effect of tDCS on the reaching ability is dependent on SABD loads in individuals with moderate to severe stroke.
Highlights
Stroke is the leading cause of disability in the United States (Roger et al, 2012)
The Z-scores of all data were in the range of ±1.96, except the normalized reaching distance for MVT_50 before the c-Transcranial direct current stimulation (tDCS) over the non-lesioned side (Z-score = −2.033)
The normalized reaching distances without data correction were used in the repeated measures ANOVA to test possible significant effects of shoulder abduction (SABD) loading, tDCS configuration (a-tDCS over lesioned side, c-tDCS and anodal tDCS (a-tDCS) over non-lesioned side, sham stimulation) and/or time
Summary
Stroke is the leading cause of disability in the United States (Roger et al, 2012). Despite novel interventions developed in recent years that emphasize task-specific repetition and increased intensity, only 20% of individuals regain normal arm function 3 months post-stroke (Kwakkel et al, 2003). In order to increase motor function, transcranial direct current stimulation (tDCS) has been tested in individuals with different pathological conditions, including stroke. One of the previous studies showed that effects of tDCS were different in mildly vs severely impaired individuals (Bradnam et al, 2012). These results suggest that the effects of tDCS may be affected by between-subject differences related to the amount of neural resources that are still available after a stroke. Never studied, within-subject differences related to the amount of neural resources that are required for different motor tasks may change the effects of tDCS in individuals with stroke
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
