**2.2. A default mode of brain function**

"Whilst part of what we perceive comes through our senses from the object before us, another part (and it may be the larger part) always comes out of our own head." William James (1890)

In classical studies of brain function, the main accepted model is based in task-evoked responses. In general, the used experiments encourage a reflexive view of how the brain works, ignoring that brain functions may be mainly intrinsic, connecting by themselves information and processing it to respond to environmental demands. By carefully analyzing the allocation of the brain's energy resources, Raichel [4] argues that the essence of brain function is indeed mainly intrinsic and components of signal transduction and metabolic pathways are all in a continuous state of flux.

Consider this functional aspect of human brain, described in Raichel's research [3, 4]:

*"In the mid-1990s we noticed quite by accident that, surprisingly, certain brain regions experienced a decreased level of activity from the baseline resting state when subjects carried out some task. These areas—in particular, a section of the medial parietal cortex (a region near the middle of the brain involved with remembering personal events in one's life, among other things)—registered this drop when other areas were engaged in carrying out a defied task such as reading aloud. Befuddled, we labeled the area showing the most depression MMPA, for "medial mystery parietal area. This cuing among the visual and auditory parts of the cortex, for instance—probably ensures that all regions of the brain are ready to react in concert to stimuli. Further analyses indicated that performing a particular task increases the brain's energy consumption by less than 5 percent of the underlying baseline activity. A large fraction of the overall activity—from 60 to 80 percent of all energy used by the brain—occurs in circuits unrelated to any external event."*

According to [3, 4], the human brain has a default mode of function controlled by a default mode network (DMN) which serves as a master organizer of its dark energy. The DMN is thought to behave like an orchestra conductor, issuing timing signals, much as a conductor waves a baton, to coordinate activity among different brain regions. This orchestrated way of doing things is described in a neat story in [4] where during a quite beach afternoon a placid tourist does daydreaming watching nowhere. In his lap rests a magazine that he's been reading for a while, suddenly a weird looking insect lands in its naked leg, firing a cascade of stimulus. The point is that during the following chains of events, where the human tries to get rid of a potential danger, the brain in fact consumes less energy during daydreaming. Raichel found that the default mode network burns energy and maintains the control of the whole body, while many other powerful neural processors (vision, sense of touch, etc.) return to the borderline of activity and keep on burning energy, ready to actuate.

The lesson about this biological brain story is that to survive in a complex physical world, our robots and robot controllers should have a safe default mode that keeps itself in charge, burns energy, preserves the mechanical structure in a safe condition, and is ready to evocate other behaviors under stimuli.
