Concepts and the default mode network
Appendix D endnote 17, from Lisa Feldman Barrett.
Some context is:
When discussing concepts, we must be mindful not to essentialize because it’s super easy to imagine concepts as “stored” in your brain. For example, you could think concepts live in the default mode network alone (as if the summaries exist apart from their sensory and motor details). There is abundant evidence (and very little doubt), however, that any instance of any concept is represented by the entire brain. [...] Some scientists try to find a compromise between these two views of concepts (that they involve sensory and motor representations versus that they are “abstract,” meaning they are stored without reference to sensory and motor details).
Sometimes, scientists try and find a happy compromise and hypothesize that the default mode network contains the true concepts, but you still need sensations and movements to trigger them. So who is correct? I think the answer depends on how you define things in the first place.
Some of the neural groupings in the the default mode network are among the most well-connected in the whole brain (i.e., they are hubs of the rich club), carrying information to and from sensory networks and coordinating processing across multiple networks. When one neuron synapses onto another, how can you know whether (1) they are part of the same network or (2) they are in different networks passing information to one another? The answer is: you can't. (Or so I've been told by every neuroanatomist I've asked.) This disagreement cannot be settled by science because it's not a scientific question. Scientists impose a functional architecture on structural connections
The best evidence that anybody has for "mental organs," that concepts live in one brain location and perceptions in another, comes from lesion studies, but as I mention in chapter 2, those studies don't take account of degeneracy. Nevertheless, when scientists assume that the brain is a collection of separate mental organs, they look at default mode network wiring and see evidence that abstract concepts live in the default mode network and are triggered by sensations and movements. In contrast, scientists who start off with more holistic assumptions about the brain's connectome, like me, see evidence that concepts are constructed by the whole brain. They are summarized in the default mode network, but the finest details stretch all the way to the sensory and motor networks. The concept cascade in figure 6-1 of How Emotions are Made depicts that process in detail. The entire cascade is an instance of a concept.
For a single human concept, whether it's "Car" or "Happiness" or "Things You Don't Bring Onto Airplanes," multiple instances of that concept in the brain will be represented, in part, by efficient neural summaries that overlap in the default mode network. The same is true of concepts that are are similar to one another, such as "Car" and "Truck," or "Happiness" and "Elation."
My view is that summarizing in the default mode network is about invariance. When multiple instances of a concept share common features, a.k.a., similarities among the different instances, they also likely share neurons.
Notes on the Notes
- E.g., see writing by Chris Eliasmith, Michael Arbib, Rolf Zwaan and Jeff Binder
- Braga, Rodrigo M., David J. Sharp, Clare Leeson, Richard JS Wise, and Robert Leech. 2013. "Echoes of the brain within default mode, association, and heteromodal cortices." Journal of Neuroscience 33 (35): 14031-14039.
- Chanes, Lorena, and Lisa Feldman Barrett. 2016. “Redefining the Role of Limbic Areas in Cortical Processing.” Trends in Cognitive Sciences 20 (2): 96–106.
- Hagmann, Patric, Leila Cammoun, Xavier Gigandet, Reto Meuli, Christopher J. Honey, Van J. Wedeen, and Olaf Sporns. 2008. "Mapping the structural core of human cerebral cortex." PLoS Biology 6 (7): e159.
- Van den Heuvel, Martijn P., and Olaf Sporns. 2013. “An Anatomical Substrate for Integration Among Functional Networks in Human Cortex.” Journal of Neuroscience 33 (36): 14489–14500.