Moving “in tune”: neuro-functional mechanisms mediating auditory-motor associations

In everyday life, our senses are constantly surrounded by many different sensory signals. Our cognitive system may combine information from different sensory modalities in order to choose the appropriate responses and ultimately promote a more adaptive behavior. A large body of research now shows that individuals exhibit consistent crossmodal correspondences between many stimulus features in different sensory modalities. Thus, the human brain shows a systematic tendency to preferentially associate certain features of stimuli across senses. The first two chapters of the present dissertation aim to investigate the human tendency to spontaneously map the pitch dimension in a spatial format, exploring the experiential bases that could modulate this correspondence. Specifically, in three different studies, we investigated whether and how prior visual experience and musical expertise impact on the pitch-space association, testing two particular populations: congenitally blind individuals and professional musicians. We found that sensorimotor experience due to musical training affects the mental representation of pitch on the horizontal space, impacting on both motor responses and the representation of peri-personal space. Conversely, prior visual experience seems not to be critical for the pitch-space association to develop, at least in the vertical dimension. In the third chapter we considered the association between auditory pitch and visual size, which refers to the finding that high-pitched sounds are perceptually associated with smaller visual stimuli, whereas low-pitched sounds with larger ones. Pushing this mapping one step further, the goal of the study described in the third chapter was to verify whether this crossmodal correspondence, reported so far for perceptual processing, also modulates motor planning. To address this issue, we carried out a series of kinematic experiments to verify whether actions implying size processing are affected by auditory pitch. Our results provide evidence for a close link between musical cognition and motor control, by demonstrating an interaction between representation of pitch dimension and representations of action-coded information for grasping, partially modulated and strengthened by musical expertise. In the last chapter of the thesis, we tested the possible causal role of different brain regions in mediating auditory-motor associations by means of Transcranical Magnetic Stimulation (TMS). Our findings showed that inhibitory TMS over premotor cortex impairs the ability to learn and apply auditory-motor associations, and that this effect is greater when a novel association must be explicitly acquired. Furthermore, we demonstrated a crucial role of the cerebellum in pitch processing, extending prior neuroimaging and neuropsychological evidence that suggest a cerebellum involvement in perceptual tasks. Overall, the findings reported in this final section provides new evidence in favor of a strong link between the perceptual and the motor systems.