Home Page Overview Site Map Index Appendix Illustration About Contact Update FAQ

Nervous System

Default State (Network)

A common perception (or misperception) about a resting brain is to assume that it is doing nothing. But according to PET scan (in the old days) and fMRI scan on hundred of volunteers, whenever the brain is not working, it switches to some kind of internal processing with a lot of activities in the prefrontal cortex and hippocampus (Figure 32). Blood flow to the brain during rest is typically just 5 - 10% lower than during
Default State task-based experiments. One theory likens it to daydream with a very serious purpose - for incorporating lessons learned in the past (by activating the hippocampus) into our plans for the future (using the higher function in the prefrontal cortex), such process is called default network. Another analogy to the activity is the idling of a vehicle : "an idling car is more ready to move than waiting for it to start up and warm up". The association of default network with very slow brain wave (0.1 Hz or less) even in sedated humans and heavily anaesthetized monkeys leads to suggestion linking it with sorting and preserving memories. Since it devours huge amounts of glucose (used up 30% more energy than other area of the brain) in the process and its impairment is related to many brain diseases, it must be very important whatever function it serves.

Figure 32 Default State
[view large image]

Go to Next Section
 or to Top of Page to Select
 or to Main Menu