Neural Basis of Social and Perceptual Decision-making in Humans

We make decisions in every moment of our lives. How the brain forms those decisions has been an active topic of inquiry in the field of brain science in recent years. In this dissertation, I discuss our recent neuroimaging studies in trying to uncover the functional architecture of the human brain during social and perceptual decision-making processes. Our decisions in social context vary tremendously with many factors including emotion, reward, social norms, treatments from others, cooperation, and dependence to others. We studied the neural basis of social decision-making processes with a functional magnetic resonance imaging (fMRI) experiment using three economic exchange games with undercompensating, nearly equal, and overcompensating offers. Refusals of undercompensating offers recruited the right dorsolateral prefrontal cortex (dlPFC). Accepting of overcompensating offers recruited the brain reward pathway consisting of the caudate, the cingulate cortex, and the thalamus. Protesting of decisions activated the network consisting of the right dlPFC, the left ventrolateral prefrontal cortex, and midbrain in the substantia nigra. These findings suggested that social decisions are the results of coordination between evaluated fairness norms, self-interest, and reward. In the topic of perceptual decision-making, we contributed to answering how diverse cortical structures are involved in relaying and processing of sensory information to make a sense of environment around us. We conducted two fMRI experiments. In the first experiment, we used an audio-visual (AV) synchrony and asynchrony perceptual categorization task. In the second experiment, we used a face-house categorization task. Stimuli in the second experiment included three levels of noise in face and house images. In AV, we investigated the effective connectivity within the salience network consisting of the anterior insulae and anterior cingulate cortex. In face-house, we discovered that the BOLD activity in the dlPFC, the bidirectional connectivity between the fusiform face area (FFA) and the parahippocampal place area (PPA), and the feedforward connectivity from these regions to the dlPFC increased with the noise level – thus with difficulty of decision-making. These results support that the FFA-PPA-dlPFC network plays an important role for relaying and integrating competing sensory information to arrive at perceptual decisions of face and house