Structure of the Brain: Does a Strongly Connected Giant Component exist?
When we think of the human brain as a large network, one natural inquiry we may have is how is it structured. Upon consideration of the structure of the web and its underlying strongly connected giant component, one may question whether or not such a giant component also describes the structure of the brain and if so, what would happen if the brain becomes separated into more than one giant component.
In understanding the network structure of the brain, scientists from Yale University analyzed brain activity in 268 separate regions through a MRI scanner for 126 participants. While each participant completed a fixed set of activities, such as remembering items to test working memory, listening to a story, solving math problems and looking at different facial emotions, the set of regions that were activated for each participant was drastically different. To address the issue of whether a strongly connected giant components exists, another set of findings by the scientists may shed some insights. The scientists discovered that many pairs of regions across the brain exhibited strong functional connection, which meant that they consistently increased and decreased their activity in tandem. Given the network mapping diagram the scientists have drawn out, one can also perceive that the brain does in fact have a strongly connected giant component but also consists of various larger clusters around regions of the brain. Another interesting discovery from the study is the uniqueness of each individual’s brain network structure. The scientists considered an individual’s brain structure as unique as his/her fingerprint, where there were consistent brain patterns regardless of the activity the individual was undertaking. This suggests that although the overall structure of the brain is a strong connected giant component, the underlying connections between nodes differ tremendously between individuals.
Functional Connectivity of the Brain as depicted by scientists involved in the study
Another question we can address is what if the strongly connected giant component gets split up or the nodes that form this giant component is damaged? In a report by a unique case where a patient had suffered reflex epilepsy, the patient developed seizures whenever he was induced by an external stimuli, such as solving a Sudoku puzzle. It turned out that the reason for these seizures was the damaging of the fibers connected to the region of the brain that was used for tempering excitation from external stimuli. This suggests that although the brain is can be considered a single giant component, it may not be strongly connected after all, as damaging a single path between nodes may mean a function is lost completely.
To read more about the studies and the case, please visit the links below:
http://www.cbsnews.com/news/the-puzzling-case-of-sudoku-induced-seizures/