IS 23. Testing cortical connectivity with multifocal TMS

Multifocal transcranial magnetic stimulation (TMS) has been recently investigated as a powerful method able to detect, within a millisecond time scale, direct information on the causal connectivity between distant cortical areas. A conditioning stimulus (CS) is first used to activate putative pathways to the motor cortex from, for example, the posterior parietal cortex or the premotor cortex, while a second, test stimulus (TS), delivered over the M1 a few milliseconds later probes any changes in excitability that are produced by the CS. When tested at rest, the activation of these cortico-cortical projections may induce either a transient facilitation or inhibition in the M1 ipsilateral or contralateral to the site of conditioning. These interactions are not fixed, but may change critically during a certain motor task, giving important information on how the strength of the connection changes over time and during a specific task, and providing crucial information on the causal effects that a specific cortical region exerts over the M1. For instance the changes in the excitability of the connections between the parietal or the prefrontal cortex with the primary motor cortex (M1) explain how their activity may modulate the pattern of output from primary motor areas preceding execution of a movement. Moreover, it is possible to combine these measurements with magnetic resonance imaging methods such as resting-state fMRI or diffusion tensor imaging (DTI) to obtain further insight...
Source: Clinical Neurophysiology - Category: Neuroscience Authors: Tags: Society Proceedings Source Type: research