Here is an issue from Scientific American that all of us in the HTM community should take a much closer look at. I happen to be subscribed to the printed version and found this cover article by Max Bertolero and Danielle S. Bassett (both at Complex Systems Group at the University of Pennsylvania) very insightful into the higher level network dynamics of the neocortex. I beleive they may help us shed some light on the H in HTM (Hierarchy).
Network Neuroscience is the new term, coined by Bassett. The article explores the recent discovery via fMRT studies of network dynamics in the cortex, which can be broken down into 7 brain modules. (I would call these modular ensembles, because these modules are not strictly isolated, localized regions). These modules have the property of always firing in sync, within the module. Each module contains nodes that tend to activate all sections within its boundaries. Graph theory and simulations run by Olaf Sporns have been applied in this study.
The seven brain modules are listed as:
- Frontoparietal Control,
- Somatic Motor,
- Default and
A series of psychological tests with given tasks, has allowed the team to understand which of these modules are involved and associated with each task-type. Some tasks linked to the visual module are, for example: Braille reading, Visual tracking, Action observation, Picture naming (silently), Brightness perception, Silent reading, etc. Interestingly, Braille reading also activates the Attention module. So some tasks activate multiple modules (ensembles). The Salience module seems to be involved in recognizing exceptions. Tasks like Breath Holding, or Awareness of need to urinate, or Stimulation monitoring or Word stem completion (silent). The Frontoparietal Control module is key to Reasoning, as in the Wisconsin Card Sorting Test, or Counting, or Tower of London (complex planning task), or Task Switching Control.
Each of these seven modules includes a set of regions, usually clustered but not always contiguous. So what keeps them together are a set of nodes (small node regions) that interlink the areas in each of the seven modules. There are also some hubs (super-nodes) that inter-connect some of the nodes across some the seven modules. (These are like bridges that connect two modules). These inter-modular hubs activate two or three of the modules during certain given tasks. The article shows the links between a long list of tested tasks (around 73) and the association of each task to some of the seven modules. The strength of these associations is also shown in the diagram.
I highly recommend reading this issue and this article. I am attaching a link to the website from Scientific American, but the aricle is unfortunately not free to access without purchase.
Look forward to some of your feedback, HTM-Community.
Kind regards, Joe Perez (in Germany)