A fundamental question that fascinates me is if the brain is unified in its perception of the world. Or is it just the sum of separate parts, like a computer?
The cerebral cortex is very plastic and can adapt to a wide variety of functions, dynamically building areas for specific functions . This plasticity extends through the entire human lifespan, so the it is fundamentally a dynamic and adaptive organism. So we see the brain has the physical abilities to form a decentralized network.
In another view of the brain, it is set up like a computer; separate parts such as the visual cortex and the motor cortex connected to the sensory organs and some sort of Central Processing Unit (CPU). So we should be able to find the “hard drive” where all the memories are stored, and a tweak fixes it and cures Alzheimer’s. Just as fMRI’s can scan the visual cortex and infer what picture a subject is looking at , we can scan the hard drive and lift memories. This explains why a hit to the head can cause extensive amnesia, the hard drive is knocked out.
However, we have not been able to find such a centralized hard drive. In fact, rats who learn to navigate a maze can still do so, after we remove up to half of their brains . This suggests that memory is stored across a distributed network spanning the entire brain. Extensive trauma to the brain often does not critically impair memory or higher order thinking, because the brain-wide network is still basically intact.
This is damning to the view that the brain is the sum of parts. If memory persists through the removal of 90% of the brain, it seems even more unlikely that there is a part from which consciousness arises. This sort of God module seems like a pipe dream of reductive materialism, when in fact consciousness is just distributed throughout the brain, without a central processing unit to direct it.
How does this network function? We don’t remember our infancy. We haven’t formed mental building blocks; basic sensory qualia such as the color red or the shape of a hand. Memory could boil down to connecting and associating these blocks. We only remember things for which we have building blocks, and without those blocks, the network does not form .
Similar to our memory-less infancy is the case of the “snap trip” in psychedelic experience, where the subject finds himself jumped hours forward, without even the vaguest sensation of passed time. The psychedelic experience may be composed of no recognizable building blocks, leading to a situation like infancy. Without basic qualia blocks, the network of memory does not form. In this view, time itself may just be another qualia.
This decentralized network would have to span the entire brain. Visual qualia exist in the visual cortex, emotional qualia in the amygdala, and movement in the motor cortex. These are located in entirely different regions. So memory is a physical network between these different regions. Even if one region is knocked out, the network still persists and memory is preserved.
More to come on the brain as a distributed, decentralized network…
1. “Patterning and Plasticity of the Cerebral Cortex” by Mriganka Sur, John L. R. Rubenstein. http://science.sciencemag.org/content/310/5749/805
2. “Scientists use brain imaging to reveal the movies in our mind” by Yasmin Anwar. http://news.berkeley.edu/2011/09/22/brain-movies/
3. “Karl Lashley”. http://www.newworldencyclopedia.org/entry/Karl_Lashley#Work
4. Late night discussions with Austin Thornbury