Aquisição simultânea de eletroencefalografia e ressonância magnética funcional para investigação da plasticidade neural

Abstract

This thesis presents a study on neuronal plasticity based on simultaneous recording of electroencephalography (EEG) and functional magnetic resonance (fMRI). There is an accumulating body of evidence indicating that neuronal functional specificity to basic sensory stimulation is mutable and subject to experience. One way to look at this plasticity is by means of perceptual learning, which is an improvement in sensory discrimination after a period of training. For that purpose, a frequency discrimination task was performed with standard and deviant tones presented to subjects. The hypothesis investigated is whether focused attention enhanced the discrimination of the deviant tones. The first original contribution of this study is that brain activity is explored during the process of learning whereas most works have investigated brain activity after relative to before perceptual learning. The results obtained show that perceptual learning can be assessed in rapid early performance having the improvement in behavioral performance as reference. Moreover, recording EEG and fMRI simultaneously provides better spatial and temporal localization of activated sources. This is important in the problem of localizing the activated sources that generated the signals measured at the scalp (inverse problem). Based on data from both modalities, this thesis employs a method in which the EEG inverse solutions are constrained to regions where fMRI indicates large hemodynamic activation. The variational hierarchical Bayesian method used overcomes problems such as false positive, incorporating fMRI information as a hierarchical prior on the variance distribution. Finally, the main contribution of this work is to show that even fast learning changes are not confined to sensory cortex, providing a potential neural substrate for top-down modulation of auditory selective attention that gives rise to auditory perceptual learning.