Cognitive focus: generalist vs specialist bias

A neocortex is loosely organized in a hierarchy of generalization: stimuli propagate from primary to association areas of both sensory & motor cortices. The minimal iterative node or "step" of generalization is probably a column or a minicolumn (see "The columnar organization of the neocortex" by Vernon Montcastle, "Cortex & Mind" by Joaquin Fuster, "On intelligence" by Jeff Hawkins). Given a relatively fixed volume & resources, the neocortex must trade between the number & the range of connections per such node. In other words, this cortical hierarchy can be relatively dense or sparse.
Generalization, or learning as distinct from passive recording, is selective: the inputs must be reinforced by matches to other concurrent or previously recorded inputs. The choice of such reinforcement is exponentially greater in a sparse hierarchy with longer-range connections. Thus, the best match will be better, increasing generality of discovered patterns. However, it will take correspondingly longer to "wire" such network, & fewer total connections means less detailed representation. So, tradeoff is between the speed & detail of learning by a dense hierarchy, & the generality of patterns/concepts discoverable by a sparse hierarchy.

A common unit of neocortex (the "iso" in isocortex) is a minicolumn: a group of ~100 neurons vertically connected across six layers of neocortex & derived from the same group of progenitor cells during embrionic development. Although lateral separation between adjacent minicolumns is disputed, they are ontogenetically distinct, & their vertical wiring & differentiation pattern is largely genetically determined. A hyper or functional column, on the other hand, is highly variable across cortex. It appears to be an emergent rather than inherited structure, defined by a common receptive field. The structure that initiates learning must be inherited & iterative, & minicolumn seems to be the only likely candidate. Given my definition of learning as generalization & prediction (for more on that see my Intelligence knol), such innate architecture would "implement" an atomic comparison/projection algorithm, iterated by vertically "chaining" minicolumns.

My insufficiently-educated guess (Langbrain, William H. Calvin, 1995) is that lateral connections among minicolumns, from layer I to layers II & III, mostly mediate lateral inhibition within a functional column, to adjust for redundancy in receptive field representation. On the other hand, the vertical connections: from layer V,VI of a source minicolumn to layer IV of a target minicolumn, via thalamus, should mediate generalization: the output should represent compressed/generalized inputs. I may be wrong on the specific nature of a node that implements an interative step of generalization, but that would not make the "sparse vs dense" premise any less valid. This premise itself depends only on the "hierarchy of generalization" premise, & I don't see any alternative to that.

I've come across three levels of evidence for neuroarchitectural differences that seem to bias cognitive focus: between brain regions, differences among individuals, & cortical features that distinguish humans & higher mammals:

The first level includes the evidence on the correlation between neuroarchitecture & cognitive bias in cortical hemispheric asymmetry. It seems that the left hemisphere represents higher-generality, especially semantic concepts, while the right hemisphere works mostly in the background, likely searching for contextual patterns (Cortex & Mind, p. 184, Split Brain, Michael Gazzaniga). The difference is mostly in degree. Accordingly, Jeffrey Hutsler and Ralf A.W. Galuske showed in "Hemispheric asymmetries in cerebral cortical networks" that macro-columns in the left hemisphere contain relatively fewer mini-columns than corresponding areas in the right hemisphere. The axons in the left hemisphere are better myelinated, even though the total volume & number of synapses is the same in corresponding areas of both hemispheres. This asymmetry seems to be greater in humans than in other animals. The hemispheres do not normally operate independently, they are densely interconnected by Corpus Callosum. Some of this connectivity is to provide simple fault-tolerance & sensory-motor field integration, as in animals. But because of greater asymmetry ("lateralization") in humans, the transfer of data between hemispheres will likely be between different levels of generality. This mismatch means that the transfer will add another level of generalization to the hierarchy of the left hemisphere.

Another type of regional differences is between prefrontal & parietal cortices: association areas of, correspondingly, motor (pressumably higher) & sensory (pressumably lower) cortices. The neocortex is myelinated sequentinally from primary to association areas at correspondingly increasing age (up to ~20 years for prefrontal cortex), & myelination then seems to decline in the same order ("Human Neurophysiology", page 197). Allowing for a multi-year delay in knowledge accumulation, this probably reflects &/or determines the age at which abilities peak in fields that require knowledge of corresponding generality. It's known that athletic abilities (primary cortices) peak in the 20s, & mathematical skills (likely parietal cortex) in the 30s. On the other hand, performance in business, politics, social sciences, & literature (prefrontal cortex?) doesn't peak until late in life. This is probably even more true in philosophy, but the performance metrics there are questionable.
Also very suggestive is the observation that such cortical development sequence is delayed by several years for ADHD subjects. Obviously, the attention span is directly correlated with the generality of discovered concepts.

A hint of corresponding architectural bias is reported here: "Neuroscientists Timothy Busch­man and Earl Miller of the Massachusetts Institute of Technology, for instance, have found two types of attention in two separate regions of the brain. The prefrontal cortex is in charge of willful concentration; if you are studying for a test or writing a novel, the impetus and the orders come from there. But if there is a sudden, riveting event—the attack of a tiger or the scream of a child—it is the parietal cortex that is activated. The MIT scientists have learned that the two brain regions sustain concentration when the neurons emit pulses of electricity at specific rates—faster frequencies for the automatic processing of the parietal cortex, slower frequencies for the deliberate, intentional work of the prefrontal." I'd speculate that higher frequency corresponds to a shorter feedback loop, - a "denser" architechture of lower levels of generalization. More generally, brain waves with higher frequencies (mostly Beta waves) are associated with a focus on speed & detail, while lower frequencies (Alpha & Theta waves) with less specific "default network" activity.

The best evidence for neuroarchitectural differences among individuals seems to come from research on autism spectrum disorder (ASD), or broader autism phenotype (BAP). Much of my info on this is via "A Shade of Gray" blog: an excellent review of relevant research, highly recommend. Among other things, BAP is known to increase a focus on specifics at the expense of higher level generalization ability, thus being a good proxy for a "specialist phenotype". 
This bias seems to be partially caused by the fact that BAP individuals have greater number of smaller & more densely packed minicolumns per macrocolumn. Their minicolumns contain the same number of smaller-size neurons, which probably drive signals over shorter range between the macrocolumns, producing local vs global connectivity bias in BAP ( from Casanova - "Abnormalities Of Cortical Circuitry In The Brains Of Autistic Individuals", via A Shade of Gray). Weaker inter-macrocolumn signals likely result in inhibited transfer of information between the levels of generalization. This would leave higher levels (associative areas) under-utilized, & my personal guess is that they will re-specialize into more "primary" areas by re-orienting toward less mediated (attenuated) specific thalamocortical inputs. Suggestive research: Partially enhanced thalamocortical functional connectivity in autism. In other words, instead of differentiating by the generality of data, the areas will differentiate by its spatio-temporal & modality-specific origin.

Very interesting study "Comparison of the Minicolumnar Morphometry of Three Distinguished Neuroscientists and Controls" by Dr. Casanova is reported in "Minicolumns, Genius, and Autism". The connectivity pattern of the neuroscientists appears to be similar to autistics in the density & size of minicolumns, but different in better inhibitory isolation between adjacent minicolumns. This should focus the output of minicolumns toward vertical vs lateral connections, increasing the vertical range even for smaller minicolumns. The other likely difference is in their corpus callosi, the structure that connects the left and right cerebral hemispheres, which seems to be smaller in autistics. Another relevant article by Claus C. Hilgetag and Helen Barbas has recently appeared in "Scientific American": Exploring the Folds of the Brain--And Their Links to Autism. It supports the premise: "in autistic people, communication between nearby cortical areas increases, whereas communication between distant areas decreases".

Yet another set of evidence is the difference in cortical architecture between humans (with obviously vastly greater generalization ability) & other animals. Beside a larger neocortex & greater hemispheric assymetry, a salient difference is the Spindle neurons, which are present only in humans &, to a far lesser extent, in other primates & whales. From Wikipedia: "Spindle cells appear to play a central role in the development of intelligent behavior and adaptive response to changing conditions and cognitive dissonance. They emerge postnatally and eventually become widely connected with diverse parts of the brain, evidencing their essential contributions to the superior capacity of hominids to focus on difficult problems." Because they're much bigger, & their axons are longer & less branched than those of pyramidal neurons, the spindle neurons should radically extend the range of vertical connections between the minicolumns. This increased range is probably not free, it should come at the expense of reduced density of connections.
However, the spindle cells span vast areas of the cortex, often connecting prefrontal & parietal cortices within a hemisphere. That means they are not a good substrate for a iterative generalization step: there's no space in the neocortex to iterate such spans. Their function is probably not directly cognitive but behavioral: balancing short-term (parietal) & long-term (prefrontal) priorities. Perhaps that's why the spindle cells in the right hemisphere outnumber those in the left one. The span of incremental cognitive generalization, on the other hand, is likely implemented by non-specific thalamo-cortical connections. Still, behavioral integrity would help "the generalist bias" by blocking short-term distractions to focus on higher-generality concepts.

Possibly more profound difference is the ratio of glia to neurons, which I think is also a good sign of a "sparse" architecture. This is an excerpt from the upcoming book "The Root of Thought": "As we move up the evolutionary ladder, in a widely researched worm, Caenorhabditis elegans, glia are 16 percent of the nervous system. The fruit fly’s brain has about 20 percent glia. In rodents such as mice and rats, glia make up 60 percent of the nervous system. The nervous system of the chimpanzee has 80 percent glia, with the human at 90 percent. The ratio of glia to neurons increases with our definition of intelligence." However, the book's interpretation of glia as as the main information processing component is very controversial. The mainstream opinion in neuroscience is still that they are mostly support cells for neurons. Thus, the increasing ratio of glia would reduce the "density" of neurons, but should enable more active longer-range connections of a "sparse" architecture.

The above discussion considered neuroarchitecturally determined trade-offs. Cognitive focus is also biased by the variation in temporal attention span. The causal mechanisms of attention span probably determine the architectural bias during cortical development. Attention span, or a stimuli "decay rate" in the neocortex, likely results from the speed of reuptake for excitatory neurotransmitters. Most likely candidates are dopamine & norepinephrine, "the pay attention" neurotransmitters, necessary for signal propagation from primary to higher association areas. The evidence here is contradictory because there are many feedback loops, but there're some interesting hints in the following study: http://jcn.sagepub.com/cgi/content/abstract/9/2/18:  To advance our understanding of attention-deficit hyperactivity disorder and medication effects we draw upon the evidence for (1) a neurotransmitter imbalance between norepinephrine and dopamine in attention-deficit hyperactivity disorder and (2) an asymmetric neural control system that links the dopaminergic pathways to left hemispheric processing and links the noradrenergic pathways to right hemispheric processing. It appears that attention-deficit hyperactivity disorder may involve a bihemispheric dysfunction characterized by reduced dopaminergic and excessive noradrenergic functioning. In turn, favorable medication effects may be mediated by a restoration in neurotransmitter balance and by increased control over the allocation of attentional resources between hemispheres. (J Child Neurol 1994;9:181-189).
I'd speculate that during prenatal / early postnatal development high levels of cortisol / low levels of serotonin increase the levels of  phasic dopamine, which in turn upregulates dopamine reuptake. This leads to greater fluctuations in the levels of tonic dopamine and increased novelty seeking, as opposed to long term focus.
It's also known that ADHD sufferers have fewer dopamine autoreceptors, leading to greater fluctuations in its levels. This probably causes lower sensitivity to to dopamine due to less efficient receptors, such as D1. Faster dopamine reuptake should reduce "vertical" signal propagation, causing constant novelty seeking for "primary" stimulation to keep the neocortex busy. ADHD can be remedied by the use of stimulants, most efficiently by reuptake inhibitors such as Bupropion.

The generalist vs specialist trade-offs are somewhat ambiguous in terms modern societal utility:

- On one hand, speed & precision was far more important for survival "in the wild", which probably explains why apes likely have a photographic memory, superior to humans: Chimps beat humans in memory test.
- On the other hand, more recent functional differentiation of modern society rewards specialization, thus precision, probably more so than a generalization ability on the opposite end of cognitive diversity spectrum.

IQ tests are inherently incapable of capturing high generalization ability because of their time limits. The tests are supposed to be background-neutral, which means they can only measure an ability to discover patterns within data given to a subject during relatively brief test (except for verbal & math IQ, which are not background-neutral). That means they’re biased toward the speed of learning, & "sparse & slow" subjects will be at disadvantage. This is conformed by the finding that lobotomy, a procedure that effectively disables prefrontal cortex (the seat of highest generalization levels), has little or no impact on IQ.
The same bias is built into an educational system: the detail-oriented "dense" subjects would be better at passive knowledge acquisition. "Sparse" architecture will excel at independent knowledge discovery & critical thinking, but this is far more difficult to evaluate. Also, modern science already accumulated a very substantial body of knowledge, which must be "passively acquired" prior to being able to make a novel discovery. This is major disadvantage for a generalist.

There's been a lot of talk about association between "genius" & autism, which I think is misleading for two reasons. First, the diagnosis of ASD is open to interpretation. It includes asocial behaviour, which is really irrelevant, - anyone with a confidence to pursue "unusual" interests will be correspondingly "asocial", be he a specialist or a generalist. It also includes "repetitive" behaviour, in which an ASD subject may focus on minute distinctions that a neurotypical observer is too "lossy" to recognize. Or, if the subject is a detached generalist, he may simply avoid "novelty" as trivial distractions, & focus on "invisible" generalizations instead.
Second, it's a lot easier to recognize & quantify exceptional abilities of a specialist than those of a generalist: we all share lower generality levels, - that's where we get the original data. On the other hand, the effective generality of the top associative levels definitely differs among individuals, & to evaluate it an observer must be a competent generalist himself. I would speculate that this is why the quality of work in social sciences, & especially philosophy, is so vastly inferior to that in "hard" sciences.

Well, if you've with me so far, this is why I researched the subject on the first place: 
A mindset for AI discovery.