Neural correlates of prior information integration in perceptual decision-making: an EEG and TMS study

Predictive coding states that perception is not a passive process but instead an active one which incorporates the prior information with the sensory information to build the perception. These two sides that form one's perceptual reality use two different, hierarchical pathways which are feed-forward and feedback mechanisms. The integration of prior information in perceptual decision-making is crucially supported by neural mechanisms that modulate brain activity in response to expectations. In this dissertation, we investigated the influence of modulation in brain oscillations on integration of prior information, which is presented right before the stimulus onset, by employing electroencephalography (EEG) and transcranial magnetic stimulation (TMS) on healthy participants performing a simple detection task. In this context, prior information refers to cues or signals presented in the form of probability bars which are shown right before the stimulus appears and they give a clue about the likelihood of target appearance in the simple detection task. Particular attention is given to the alpha range (8-13 Hz) in the pre-stimulus time interval (-400 to 0 ms) in order to observe the changes in anticipation of the stimulus. The analysis of EEG data revealed significant alpha and low-beta power desynchronization in the pre-stimulus period between different prior information conditions prior to continuous theta burst stimulation (cTBS) application. However, this modulation was absent in post-cTBS, suggesting that inhibition of the posterior parietal areas disrupts the brain's ability to integrate prior information, as reflected in alpha and low-beta band activity. On the contrary to these findings, SHAM group does not reflect the expected outcome completely. Our findings contribute to the broader understanding of how the brain integrates expectations into ongoing cognitive tasks and the markers of this process.