Neural Mechanisms Underlying the Integration of Visual and Proprioceptive Perception, Attention, and Motor Control During Voluntary Reaching Movements

Voluntary movements are required to interact with the world around us. In order to perform precise interactions, it is necessary to integrate correctly sensory feedback of different modalities, filtered by attention. Sensory signals like vision and proprioception are essential to monitor the world and to interact with it through the means of different effectors, such as arm movements. Attention is instead a core cognitive mechanism that filters and prioritizes relevant sensory data within a given context, ignoring irrelevant noise at the same time. Among the various forms of attention, spatial attention plays a crucial role in everyday life. By highlighting what matters, spatial attention helps us understand the world effectively, supporting adaptive behavior and ultimately promoting survival. Therefore, vision, proprioception and spatial attention are fundamental components of human cognition, essential not only for perceiving the environment but also for enabling dynamic interaction with it. When effectively integrated with motor planning, these processes support real-time adjustments and enable precise, goal-directed actions. However, the neural mechanisms underlying the integration of perception and of attention with motor control are far from being fully understood. Over the years, increasing interest has been directed toward the posterior parietal cortex (PPC), a region of the brain known for its remarkable integrative functions. It is known that the PPC processes and combines various sources of information, including visual, attentional, and proprioceptive inputs, to support a wide range of functions. These include movement planning, real-time movement adjustments, spatial awareness, navigation, and many others. Its complex role makes the PPC a key relay station in the coordination of action and perception. Nevertheless, the precise functional specialization among PPC subregions remain largely unknown. To investigate the causal role of the PPC, with a specific focus on its medial part, in mediating the interaction between sensory processing, attention, and voluntary motor control, I conducted a series of experimental studies on healthy human participants during my doctoral research. In the first study, conducted at the University of Bologna, I delivered online repetitive transcranial magnetic stimulation (rTMS) to understand the causal role of areas hV6A and hPEc of the medial PPC while participants performed reaching corrections guided by visual or by proprioceptive feedback. The findings revealed a functional specialization within the medial PPC, demonstrating that these subregions are differentially engaged in processing specific types of sensorimotor information during corrective motor actions. In the second study, also conducted at the University of Bologna, I applied rTMS to investigate the causal role of hV6A in the interaction between spatial attention and reach planning. The results demonstrated that hV6A plays a critical role in linking 7 spatial attention with motor intention, while not being essential for reach planning or sustained attention when considered independently. A third study was conducted during an 8-months period as a visiting PhD student at the Active Perception Laboratory at University of Rochester, under the supervision of Professor Martina Poletti. In this behavioral study, I have found that microsaccades, tiny gaze shifts occurring during fixation, are differently modulated during motor planning than during a basic attentional task, suggesting that the neural mechanisms underlying their generation are differentially influenced by motor preparation compared to spatial attention. To summarize, this dissertation investigates the intricate neural processes behind multisensory integration, attention and motor control, with a particular emphasis on the role of the medial PPC. Grounded in the research I conducted throughout my PhD, this work offers insights into how visual, proprioceptive and attentional mechanisms, along with motor processes, relate to each other. This knowledge is essential not only for advancing fundamental neuroscience, but it is also crucial for future applications in fields such as neurorehabilitation and neural prosthetics.