AbstractsPhysics

This thesis focuses on audiotactile integration, brain areas activated by vibrotactile stimulation, transfer of vibrotactile information to motor output, and reactivity of the human primary motor and somatosensory cortices in action observation. Human experience of the outside world results from integration of information obtained simultaneously via multiple senses. Accumulating evidence, from studies in both primates and humans, suggests that integration between different sensory modalities also occurs at early stages of cortical processing, in areas classically considered as purely unisensory. In Study I we studied integration between auditory and somatosensory systems. We showed, in a loudness-matching task, that subjects chose lower intensities for the probe than for the reference tone, when auditory and vibrotactile stimuli were presented simultaneously. In Studies II and III we explored brain areas involved in processing vibrotactile and tactile information, respectively. We showed that, besides primary and secondary somatosensory areas, auditory areas are also activated. In Study II we characterized the time course of brain activations and showed convergence of vibrotactile information to auditory areas. On the other hand, in Study III we identified, with good spatial accuracy, common neural substrates that process auditory and tactile information in auditory belt areas. In Study IV we assessed whether frequency information transfers from touch to vocal utterance in normal-hearing female adults. We demonstrated that such information transfer occurs clearly between 150–400 Hz. Based on findings in Studies II and III, we hypothesized that this transfer may involve at least primary and secondary somatosensory and auditory areas. Our social skills rely on the capability to understand others. In the human brain, the mirror-neuron system matches observation and execution of actions. This system comprises at least the inferior frontal gyrus, premotor areas, primary motor cortex, and the inferior parietal lobule. In Study V we investigated similarities in sensorimotor oscillatory activity between own, observed, and heard actions. We demonstrated that the primary motor cortex is activated before own and observed actions and stabilizes similarly. We also showed that rhythmic activity in the primary somatosensory cortex recovers later during own actions, which may be related to proprioceptive input and contribute to maintaining the sense of agency.