The quantitative spatiotemporal relationship of whole brain activity of human brains revealed by fMRI

Human brain consists of many functional systems from the essential sensory, motor, attention and memory systems to higher order cognitive functions such as reasoning and language. Performing even a simple task may evoke multiple systems and cognitive functions, resulting in a whole brain activity across the entire brain. Despite the importance of studying task-evoked brain activated networks, investigating this whole brain activity may be crucial for understanding the neural bases of individual behavioral and clinical traits. BOLD-fMRI measures the four-dimensional (3 spatial and 1 temporal) neural activity across the entire brain at large-scale systems level. All local activities across the entire brain constitute the whole brain activity and each local activity is a part of that whole brain activity. Unlike a local activity that is characterized by its temporal neural activity, the whole brain activity is characterized by its spatial variation across the entire brain. We present a novel data-driven method to analyze the whole brain activity when performing tasks. The method enabled us to analyze the whole brain activity for each task trial and each individual subject with no requirement of a priori knowledge of task-evoked BOLD response. Our study revealed a quantitative spatiotemporal relationship of the whole brain activity with the local activities. The whole brain activity demonstrated a remarkable dynamic activity that varied from trial to trial when performing the same task repeatedly, showing the importance of analyzing the whole brain activity for investigating the neural bases of personal traits.