Understanding the neural mechanisms underlying action perception and dopaminergic modulation in the human brain

This thesis focuses on the neural mechanisms involved in action perception and motor cognition, combining the outcomes from object-based spatial correspondence effects and dopaminergic modulation through transcranial magnetic stimulation (TMS). The first section investigates how tool-object pairs are spatially coded in the human brain, demonstrating that perceptual grouping, rather than affordance-based action, causes response facilitation. The study explores how the motor interactions with both single tools and tool-object pairs are influenced by visual asymmetries created by protruding parts of the objects, not limited to just the handle. It was found that performance in tasks was faster and more accurate when the spatial responses correspond to the location of these protruding parts, highlighting the concept of object-based spatial correspondence effects. Two experiments were conducted to explore the mechanisms behind the spatial coding of tool-object pairs, particularly when semantic relationships and action alignments were manipulated independently. The results indicated that the spatial correspondence effects observed were dependent on the location of the protruding side of the tool-object pairs, rather than the non-protruding side of the tool handle. This supports the location coding account of the effects, challenging the affordance activation account, which suggests that the handle's orientation should drive the effects. The findings suggest that semantic relations and action alignments function independently as criteria for perceptual grouping, allowing the basic spatial coding of visual asymmetries. The second section of the thesis explores the neuromodulatory effects of excitatory intermittent theta burst stimulation (iTBS) on the release of endogenous dopamine in the striatum. Employing positron emission tomography (PET) imaging with 18F Desmethoxyfallypride (DMFP)- a dopamine receptor antagonist, it is demonstrated that time-spaced repeated blocks of iTBS to the left dorsolateral prefrontal cortex (DLPFC) enhance fronto-striatal connectivity and the release of endogenous dopamine in a dose-dependent manner. This scheme could provide an alternative to unpleasant and distressing long stimulation protocols in experimental and therapeutic settings. Specifically, it was demonstrated that three repeated bouts of iTBS, spaced by short intervals, achieve larger effects than a single stimulation. This finding has implications for the planning of therapeutic interventions, such as the treatment of major depression. By integrating cognitive-motor interactions with neuromodulation , this thesis provides a comprehensive framework for a deeper understanding of how spatial cognition and dopaminergic brain networks shape human action perception and decision-making and clinical neuromodulation.