Guest post by Robin Stevens Payes
“The default brain relates to the fact that your brain is conscious all of the time, regardless of whether you’re awake or asleep or engaging in a particular activity or daydreaming. The brain is engaged pretty much at full capacity all of the time.” So summarizes Marcus Raichle, M.D., researcher and faculty member at the Washington University in St. Louis School of Medicine, in defining the brain’s default mode network (DMN).
Raichle was at the Carnegie Institution for Science in Washington, DC, on December 8, giving this year’s Kavli Lecture in Neuroscience on the topic “The Restless Brain.” The Dana Alliance member, who received the 2014 Kavli award that he shares with fellow Dana Alliance member Brenda Milner, Ph.D., and John O’Keefe, Ph.D., was met by an enthusiastic overflow crowd.
Raichle and his lab first detected and deciphered the DMN, showing that when we are in a quiet non-focused state of mind, many brain areas keep percolating and interacting, countering the then-standard idea that the resting brain must show less electrical or metabolic activity than a task-oriented brain. Drawing on his key discovery of the DMN, he has observed that the brain exhibits a high level of “intrinsic activity,” meaning that most of what the brain’s doing, it’s doing all the time.
The DMN is only one of several brain networks that have now been identified and shown to be interconnected. Others include executive control, visual, auditory, salience, sensorimotor, and dorsal attention (playing an important role in selecting visual information based on internal expectations or the sensory salience of visual object) networks. Much of Raichle’s latest work is trying to understand this interconnectivity—how these networks “talk” to one another to make up total neural function.
Based on his work and that of others, he concludes that our earlier understandings about brain function, typically drawing from task-focused experiments that demonstrate activity in specific brain regions, “ignores the alternative possibility that brain functions are mainly intrinsic and ongoing, involving information processing for interpreting, responding to, and predicting environmental demands.”
During his talk, Raichle covered the history of brain discoveries in these areas and offered glimpses into future research. A sampling of insights and implications from findings by Raichle and his colleagues:
The brain is a vast consumer of energy. While the brain represents about 2 percent of total body weight, it accounts for 20 percent of all the energy consumed, 10 times that predicted by its weight alone, Raichle said, citing his 2015 paper, “The restless brain: how intrinsic activity organizes brain function.”
When we are 10 years old, our brain consumes 50 percent of the body’s energy. “We need to protect it,” Raichle said, pointing to the fact that young brains are especially vulnerable to injury in contact sports.
Electrical activity in the resting brain shows that its activities “are mainly intrinsic, ongoing, costly, and largely non-conscious.”
Conscious perception is limited. In the 2015 article Raichle noted that, “…visual information is significantly compressed as it passes from the eye to the visual cortex.” Perception enters the visual center of the brain as a sort of low-resolution file for all the information that exists in our environment. There is a lot that goes on outside of our conscious awareness.
The brain functions as a prediction machine. It draws on the scanty information drawn from the low-res sensory download and communication across brain networks to revisit what it’s likely to see in the future. The brain is “intrinsically organized in space and time,” Raichle observes.
Understanding normal brain functioning and connectivity may help us understand brain diseases including autism, ADHD, Parkinson’s, and Alzheimer’s disease, and perhaps point to methods of prevention and treatment.
“To me, it’s been an amazing adventure to be at the table when all of this has unfolded, as we think of human behavior and our understanding of why we do what we do, and why we feel what we feel,” Raichle concluded. “In the vast majority of [the brain’s] ongoing activity—anticipating your every need—it’s going about its business without your conscious awareness.
“The brain is like an iceberg. The majority of what we see is the minority of what’s really there. We have an immensely interesting and challenging task before us.”
The recorded lecture is available to view online in its entirety: http://library.fora.tv/2015/12/08/Kavli_Laureate_Lecture_-_The_Restless_Brain