Functional Connections of Cortical Areas: A New View from the Thalamus

Depending on the gender, there are 302 or 385 neurons in C. Elegans, a nematode with 1000 cells in its body. Even with this animal, it isn’t known how its central nervous system produces the ensemble of its behaviors. In an era where the technology exists to beat the best human player at several games (closed systems) where creativity is involved, to produce transistors with gate lengths spanning tens of atoms, and to alter species’ genetic code, why does this remain a mystery?

Perhaps one reason could be epistemological? If one thinks of the brain as a computer, one will project metaphors from computing onto its study. Neurons will be like transistors. Neural activity like boolean logic. It seems to me like the state space resulting from treating those 302 or 385 neurons as a circuit is relatively small, vs a dynamical system having a temporal component (akin to “if neurons are instruments, consciousness is a symphony”). Then, the state space becomes enormous: in terms of assigning causation of some output behavior to an input configuration, it would not be a snapshot of state, but how the neural activity evolves between points in time.

In any case, I only sort of know what I’m talking about. So don’t quote me…

But this, just the study of the exact neural correlates of behavior for the most simple organism, that’s anywhere from someone’s PHD to an entire career.

How many horizons will there be, before the human brain can be fully understood? To illustrate what I mean,

new discoveries are constantly changing the previous picture. For one example, the thalamus is thought to be a relay center from the senses to the cortex, although besides afferents it also contains cortical-cortical pathways. Cortical areas are already wired up to other cortical areas directly, so why have additional (thalamocortical) wiring?

Evolution is so different than a human designer, as it builds on more ancient [mechanisms, circuits, pathways] rather than designing from scratch. For instance, there are three copies of all information that reaches the spinal cord: one goes to the most ancient central pattern generators residing in the spinal cord and brain stem (which produce walking, reflexes, heartbeat, chewing, etc), the second goes to the more modern cerebellum, which is nowadays thought of as an adaptive filter (both modulating a signal and reporting the difference between expected and observed back to the cortex), and the third goes through the thalamus to the cortex (my guess is that this pathway could be involved in concept formation and other aspects of cognition). For cortical efferents (IE sensorimotor drivers) it is similar: one copy to the cerebellum, one directly to the spinal cord, one through the thalamus towards other cortical areas.

The way dendritic spines and glial cells (astrocytes, microglia) create and remodel synapses on different timescales is another.

https://www.goodreads.com/book/show/17349913-functional-connections-of-cortical-areas