General results of the project
We explored the fundamental mechanisms behind processing of auditory sounds. We showed that processing language information is strongly affected by the mother tongue of the perceiver, most probably due to experiential differences during early language development and formation of memory traces. In language with tonal properties, the processing of pitch is supported by brain networks involved in speech processing, whereas in the non-tonal language pitch is processed differently. In language with clear distinction between voiced and unvoiced consonants perceivers are more sensitive to the voicing properties in speech. These results are important for diagnostic tools or study protocols where language-related material is used. To clarify which stimuli to use in clinical and laboratory settings, we compared natural and computer-based synthesized stimuli, and showed the preferred perception of natural stimuli. We investigated the plasticity of auditory system and its structural and metabolic determinants using the mismatch negativity (MMN) paradigm, which reflects the brain’s automatic response to changes in stimulation. Drug challenge studies indicate that NMDA receptor-mediated synaptic plasticity is particularly involved in the MMN, therefore we studied the role of excitatory neurotransmitter glutamate and showed for the first time that the inter-individual variation in the glutamatergic neurotransmission affects the MMN in healthy individuals in the absence of pharmacological manipulation. We also showed an increase in the MMN amplitude after rapid, short-term LTP-like auditory training. The mechanisms of cortical plasticity following training are important to study due to their importance for learning and memory, as well as possibilities for intervention in case of disturbances in sensory processing.