P258 Combining tDCS with prismatic adaptation for non invasive neuromodulation of the motor cortex

Introduction: Prismatic adaptation (PA) shifts visual field laterally and induces lateralized deviations of spatial attention. Recently, it has been suggested that prismatic goggles are also able to modulate brain excitability (Magnani, 2014), with cognitive after-effects documented even in tasks not necessarily spatial in nature (Oliveri, 2013). Objectives: The aim of the present study was to test whether prisms can modulate motor cortical excitability similarly as anodal transcranial direct current stimulation (tDCS) does; to test whether neuromodulatory effects obtained from tDCS and prismatic goggles could interact and induce homeostatic changes in brain excitability. Materials and methods: Twenty-four subjects were submitted to single-pulse transcranial magnetic stimulation (TMS) over the right M1 to measure their Input–Output (IO) curve as a measure of cortical excitability (Carroll, 2011). Assessment was made in three experimental groups: before and after rightward PA; before and after atDCS of the right M1; before and after rightward PA and atDCS of the right M1. Results: A significant increase of the steepness of the IO curve slope on the right motor cortex was found following either rightward PA or atDCS; on the other hand, a decrease of the steepness of the IO curve slope was found after the combination of rightward PA and atDCS. Conclusion: These findings suggest that PA could be an additional tool to modulate cortical plasticity in motor cortices and that an increase or a decrease in corticospinal excitability depends on the functional state of the M1 before or at the time of conditioning (Lang, 2004).