Prism Adaptation-Induced Modulation of Cortical Excitability of Upper and Lower Limb Muscles is Enhanced with Electrical Stimulation
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Background
Prism adaptation (PA) is a behavioral training paradigm shown to induce immediate changes in visuospatial and motor function. PA may modulate the input and output stages of processing spatial cognitive information. However, the cortical plasticity mechanisms related to the behavioral effects of PA are poorly understood. Non-invasive sensorimotor electrical stimulation (Stim) may upregulate corticomotor excitability and is commonly used as a therapeutic adjunct during motor training.
Objective
To evaluate the effects of combining PA with Stim on corticomotor excitability and visuo-spatial-motor behavior.
Methods
We used a repeated-measures design to evaluate the effects of 1 session of PA with and without Stim in 15 young able-bodied individuals (18-35 years). Corticomotor output, intracortical inhibition, and facilitation were evaluated before and after PA with motor-evoked potentials (MEPs) elicited from single and paired-pulse transcranial magnetic stimulation (TMS) delivered to M1 hotspots of bilateral upper and left lower limbs.
Results
Behaviorally, both PA+Stim and PA+Sham showed significant sensorimotor aftereffects (visuo-spatial and proprioceptive pointing). Neurophysiologically, suprathreshold MEP amplitude increased in the left first dorsal interossei, left tibialis anterior, and left soleus following the PA+Stim condition compared to the PA+Sham condition. Additionally, following PA+Stim, Short Interval Intra-Cortical Inhibition (SICI) increased in the left tibialis anterior and left soleus.
Conclusion
Although both PA+Stim and PA+Sham had similar behavioral aftereffects, only PA+Stim increased cortical excitability in M1 representations of the left upper and lower limb (toward the direction of the PA aftereffect), suggesting that PA+Stim may elicit greater neurophysiological changes than PA alone.
