T004 Cognitive processes of motor behavior revealed by tDCS

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive tool, which effectively modulates behavior, and related brain activity. When applied to the primary motor cortex (M1), tDCS affects motor function, enhancing or decreasing motor learning and action execution in both healthy participants and brain-damaged patients. Evidence in both humans and macaques has shown that multiple cortical areas beyond M1 are involved in controlling and guiding movement, including the posterior parietal cortex (PPC) and the premotor cortex (PMC). Recent evidence in healthy humans and brain-damaged showed that the modulation of cortical excitability of PPC and PMC can be used to improve action-related cognitive processes, highlighting interesting hemispheric asymmetries. Indeed, the anodal tDCS of the PPC of the left hemisphere can be used to selectively facilitate action planning and gesture recognition, while excitability shifts within the PM of the right hemisphere affects action monitoring and awareness. These results indicate that a left parietal system contributes to the activation of motor engrams (such as the pattern and sequence of movements needed to execute an action), while left premotor areas are mostly involved in the operation of the motor monitoring, namely detecting the mismatch between the actual motor output and intended action goal. The final relay is M1, which converts the motor program into the desired action. In conclusion, this evidence offers a functional and anatomical framework for understanding how selective neuromodulatory effects on different higher-level (action planning and monitoring) stages of motor processing can be induced by tDCS in order to optimize motor control and learning. This knowledge opens up novel perspectives in the neurorehabilitation of stroke patients with apraxic and motor awareness disorders, which represents a considerable burden for motor and cognitive rehabilitation.