Date(s) - 07/10/2013
Title: Single-trial analysis and its applications in EEG and simultaneous EEG-fMRI studies
Electrophysiological recordings such as human electroencephalogram (EEG) and monkey local field potentials (LFP) are traditionally thought to be comprised of a deterministic event-related potential (ERP) plus a task-irrelevant random noise. However, evidence has long suggested that the ERP waveform can vary from trial to trial. Such trial-to-trial variability often bears important information about the dynamics of the underlying cognitive processes. With recent advancements in single-trial analysis methods, we seek to explore in this dissertation the dynamics of cognitive processes underlying higher-level cognitive functions including visual attention, emotional processing, and classical conditioning.
First, we applied a recently developed single-trial analysis method, Analysis of Single-trial ERP and Ongoing signals (ASEO), to study the trial-to-trial temporal dynamics of sensory facilitation during classical aversive conditioning. Estimating the amplitude of the P1 component elicited by the conditioned stimuli (CSs), we found that P1 amplitude fluctuations within the acquisition session followed three distinct phases. Further, the effects of sensory facilitation toward the CS predicting aversive outcomes, compared to the CS predicting neutral outcomes, were manifested by differences in the rate of P1 amplitude changes within each phase. Second, we investigated brain structures involved in the generation and modulation of the late positive potential (LPP) during emotional processing. Correlating single-trial LPP amplitude with the simultaneously recorded blood-oxygen-level-dependent (BOLD) activity, we found that regions contributing to scalp-recorded LPP included the visual cortices and emotional processing structures. Moreover, the degree of contribution to scalp LPP from these structures was valence specific. Finally, we investigated brain areas contributing to the attentional modulation of alpha (8–12 Hz) in spatial visual attention. Our results suggest that the intraparietal sulcus, a core region within the frontoparietal attention network, modulates the trial-to-trial alpha desynchronization. Further, we found a positive correlation between alpha lateralization and BOLD in dorsal anterior cingulate cortex (dACC), suggesting a role for dACC in facilitating the attentional set via executive influences over attentional control systems.
In conclusion, the results suggest that trial-to-trial variability is an important aspect of the cognitive process. Exploring such variability can gain us valuable insights into the neuronal mechanisms of higher-level cognitive processes.