An Information System in the Brain: Evidence from fMRI BOLD Responses

In this study, we will show in three visual experiments that there are several brain regions in which induced blood oxygenation level-dependent (BOLD) responses are reproducible between visual tasks and between individual subjects. The reproducible BOLD responses indicate that the specific-sensorial structure (e.g., the lingual gyrus) and non-specific structure (e.g., the precuneus) both exhibit increased and decreased BOLD responses, while the associative structure (e.g., the intraparietal sulcus) shows only increased responses. The response patterns remain stable even during task switching from visual-spatial attention to central eye-fixation. Based on the response patterns in different cortical structures, this study will discuss two issues pertinent to applying BOLD contrast to research on high-level cognitive functions. First, there may exist a large-scale information system reproducible between visual tasks that only affect changes in the response sign in the system nodal regions (i.e., positive or negative BOLD responses). If the information system remains faithful to all visual tasks, localization of cognitive functions might not be a priority in functional magnetic resonance imaging (fMRI) studies. Second, the reproducible BOLD responses have partially reflected functional roles of neurotransmitter systems in different cortical structures. Recent studies using MR spectroscopy have suggested that γ-aminobutyrate (GABA) activity is negatively correlated with BOLD responses. Since GABA concentration is relatively low in the associative regions as compared with that in other regions, the spatial resolution of BOLD signal may be insufficient in recovering possible negative activity in the associative regions. This also calls special attention to a recent discovery on glutamateand GABA-mediated signaling in regulating blood flows and BOLD signal changes. We conclude the study by hypothesizing three inter-related functional loops for future research on the information system using BOLD contrast.