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This is: How uniform is the neocortex?, published by Alex Zhu on the AI Alignment Forum.
How uniform is the neocortex?
The neocortex is the part of the human brain responsible for higher-order functions like sensory perception, cognition, and language, and has been hypothesized to be uniformly composed of general-purpose data-processing modules. What does the currently available evidence suggest about this hypothesis?
"How uniform is the neocortex?” is one of the background variables in my framework for AGI timelines. My aim for this post is not to present a complete argument for some view on this variable, so much as it is to:
present some considerations I’ve encountered that shed light on this variable
invite a collaborative effort among readers to shed further light on this variable (e.g. by leaving comments about considerations I haven’t included, or pointing out mistakes in my analyses)
There’s a long list of different regions in the neocortex, each of which appears to be responsible for something totally different. One interpretation is that these cortical regions are doing fundamentally different things, and that we acquired the capacities to do all these different things over hundreds of millions of years of evolution.
A radically different perspective, first put forth by Vernon Mountcastle in 1978, hypothesizes that the neocortex is implementing a single general-purpose data processing algorithm all throughout. From the popular neuroscience book On Intelligence, by Jeff Hawkins[1]:
[...] Mountcastle points out that the neocortex is remarkably uniform in appearance and structure. The regions of cortex that handle auditory input look like the regions that handle touch, which look like the regions that control muscles, which look like Broca's language area, which look like practically every other region of the cortex. Mountcastle suggests that since these regions all look the same, perhaps they are actually performing the same basic operation! He proposes that the cortex uses the same computational tool to accomplish everything it does.
Mountcastle [...] shows that despite the differences, the neocortex is remarkably uniform. The same layers, cell types, and connections exist throughout. [...] The differences are often so subtle that trained anatomists can't agree on them. Therefore, Mountcastle argues, all regions of the cortex are performing the same operation. The thing that makes the vision area visual and the motor area motoric is how the regions of cortex are connected to each other and to other parts of the central nervous system.
In fact, Mountcastle argues that the reason one region of cortex looks slightly different from another is because of what it is connected to, and not because its basic function is different. He concludes that there is a common function, a common algorithm, that is performed by all the cortical regions. Vision is no different from hearing, which is no different from motor output. He allows that our genes specify how the regions of cortex are connected, which is very specific to function and species, but the cortical tissue itself is doing the same thing everywhere.
If Mountcastle is correct, the algorithm of the cortex must be expressed independently of any particular function or sense. The brain uses the same process to see as to hear. The cortex does something universal that can be applied to any type of sensory or motor system.
The rest of this post will review some of the evidence around Mountcastle’s hypothesis.
Cortical function is largely determined by input data
When visual inputs are fed into the auditory cortices of infant ferrets, those auditory cortices develop into functional visual systems. This suggests that different cortical regions are all capable of general-purpose data processing.
Humans can learn how to perform forms...
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