Depending on the goal of the task -- whether subjects were asked to make an orthographic (spelling) judgment or a phonological (rhyming) judgment ?the Northwestern researchers found that different convergence zones in the network were involved in the task.
"The existence and the identity of convergence zones --areas in which information from multiple sources meets in the brain -- have been debated since they were proposed in the late 20th century," said Bitan. "Now, with new techniques to analyze brain imaging data, we can examine the specific role played by different brain regions in the network that are required for any cognitive task. These techniques examining effective connectivity enable us to learn how the brain changes its interconnectivity according to the task at hand."
The Northwestern researchers also propose to explain the role of each brain region as it interacts within a complex network to achieve a specific cognitive goal.
The conventional method for analyzing fMRI data, which can only show which brain regions are active in a given task, showed two brain regions that were specifically active for each of the studied tasks: the lateral temporal cortex (LTC) for the rhyming task and the intraparietal sulcus (IPS) for the spelling task.
In addition to the task-specific regions, the inferior frontal gyrus (IFG) and the fusiform gyrus (FG) were engaged by both tasks. Dynamic Causal Modeling, the new method examining the influences between brain regions, indicates that each task preferentially strengthened the influences converging on the task specific regions (LTC for rhyming, IPS for spelling). This finding suggests that task specific regions serve as convergence zones that integrate information from other parts of the brain.
The results also show that switching between tasks -- in this case between rhyming and spelling -- led to changes in the influence of th