Speaker
Description
The introduction of the TMS cortico-cortical paired associative stimulation (ccPAS) technique has spurred a paradigm shift in the study of brain connectivity: ccPAS targets cortical pathways, repeatedly stimulating nodes to transiently enhance/hinder their coupling, exploiting Hebbian spike-timing dependent plasticity. This allows manipulation of cortical networks, to study their physiological characteristics and functional relevance from a causal perspective.
The aim of this thesis is to leverage ccPAS to deepen the understanding of human visuomotor circuits, focusing on the pathway between the ventral premotor (PMv) and primary motor cortex (M1). Through its copious projections to the M1, the PMv is believed to be crucial for various visuomotor behaviors, such as arbitrary visuomotor mapping and hyper-learnt visuomotor associations underlying automatic imitation. Yet, causal evidence for the PMv-to-M1 network's functional relevance is limited.
A first series of studies investigated the physiological bases of ccPAS, and tested how it can affect the strength of effective connectivity and excitability of targeted areas. Secondly, we focused on the role of the PMv-to-M1 circuit in forming visuomotor associations. The application of brain-state-coupled ccPAS demonstrated the relevance of PMv-to-M1 connectivity to arbitrary visuomotor mapping, and the combination of ccPAS with behavioral paradigms used to study automatic imitation provided causal evidence of the pathway’s role, within the action observation network, in automatic imitative behavior. Finally, we combined dual-coil TMS connectivity assessments and ccPAS in young and elderly individuals to trace the connectivity, plasticity, and relevance of premotor-motor networks to manual dexterity and strength in aging. In healthy elderly adults, we observed that a decline in connectivity and plasticity of the motor system predicted a decline in manual motor functions.
These findings highlight the efficacy of ccPAS in modulating cortical connectivity and behavior, offering valuable insights into visuomotor circuits. The research paves the way for clinical interventions based on connectivity manipulation.
