Importance of cortical spacing

I’m a real sceptic of supposed dichotomies in brain processing. I think they are often so simplistic as to be misleading and incorrect, and ultimately lead to such profound misunderstandings, supposedly ground in science, as to be actively damaging g (c.f gender differences – aka neurosexism – left/right brain processing, etc). However, I may well be a convert over big picture-fine grained brain processing, which is rooted in the understanding of cortical minicolumns.

The cortex in the brain is arranged into minicolumns, made up of between 80 and 100 neurons sitting in a vertical column (Mountcastle, 1997). The neurons within a column work together to excite or inhibit electrical signals. The fascinating aspect of these minicolumns is that they are regularly spaced throughout the cortex which turns out to have a fairly profound impact on processing skill. Although minicolumns are regularly spaced throughout an individuals cortex (by which I mean, the minicolumns are spaced at the same interval)* this distance varies between individuals. The spacing distance directly correlates with the length of connections that are made between columns: Those with relatively wide spacing between their minicolumns have longer axonal connections down which an electrical signal travels to be passed on; those with relatively narrow spacing have shorter axonal connections (Casanova, & Williams 2010).

This sounds a mundane, even trivial point: if minicolumns are packed tighter together then of course the distance the axons need to span is shorter to connect to the same number of minicolumns as compared to a looser packing of columns. However, the reality is that this is no trivial relationship and the larger impacts of the spacing of minicolumns and the length of axonal connections permeate through to the very way that we experience the world we inhabit.

Michael Casanova in particular has been key in demonstrating the variability of minicolumn spacing and the implications this has (see for example, Williams & Casanova, 2010; Opris & Casanova, 2014). He suggests that the spacing of minicolumns is distributed across a bell curve in the human population, and as in all bell curves the edge cases at the tails can tell us something interesting. Casanova has found evidence that at the two extremes of minicolumnar spacing there is a very different way of interacting with the world. Densely packed minicolumns has been associated with autistic spectrum disorder (ASD) and loosely packed minicolumns associated with dyslexia (Casanova et al 2002a and 2002b). Along with denser packing of minicolumns in ASD, axonal connections are also shorter, and vice versa in dyslexia. Although these two disorders aren’t commonly considered part of the same continuum, perhaps this neuroscientific finding sheds light on the peculiarities of these types of brain processing, and in turn sheds light on the differences that exist between all of us.

A disproportionate quantity of innovators, artists (novelists, painters, musicians, …) entrepreneurs, scientists, game changers are dyslexic. Some parts of dyslexic processing can be characterised as big-picture thinking: making unusual connections between different areas, seeing patterns between superficially disconnected topics, visualising the path from beginning to end, clearly, without being hung up on the fine detail. Lack of skilled fine detail processing can also be characteristic of dyslexia: struggling with phonics – the smallest elements of words – and how they combine to form words, having difficulty with symbol differentiation – confusing b/d when reading, writing letters and symbols the wrong way round, etc. – problems, in short, with the fine detail of reading and writing. (For more on this, see Eide & Eide, 2011).

Conversely, high-functioning individuals with ASD tend to get obsessively caught up with the fine detail, making extraordinary mathematicians, scientists, techies where strong academic abilities coupled with an ability to sift through reams of technical details plays to their strengths. Equally, the social difficulties often experienced by those with ASD can be cast as a failure of big-picture thinking: small behavioural clues get wound together in a rich behavioural pattern from which typically functioning individuals can interpret inner states and motivations with varying degrees of success. The more low-functioning characteristics of ASD can also be understood in these terms: repetitive actions are indicative of a need for focus on the minimal details and an inability to countenance even small changes to routine demonstrating an inability to recognise that a different pattern of activity can lead to the same end point.

If the hypothesis that these two types of brain functioning are in fact two extremes of the same continuum that every individual is on (afterall, we all have minicolumns spaced at some interval) then we must all fall on this continuum somewhere. Because minicolumn density distribution is a bell curve, most of us will fall in the middle, with similar natural abilities in both big-picture and fine-detail processing , but let me caveat this, with pure conjecture. It may well be that we all have at least a small preference for one type of thinking: perhaps I am slightly to the more densely packed side of the bell, perhaps you are slightly to the more loosely packed side. It’s not clear whether these small differences would make a profound difference or not, but let’s assume that there is at least a very slight natural preference. The brain, like all the muscles in our body, requires practice at tasks to get better at them. In everything, we naturally favour the task or activity which is slightly easier. So, if I have a very slight disposition towards fine-detail reasoning, over time I will practice this more than I practice big-picture thinking, widening the gap between my ability to think in fine detail as compared to big-picture.

I’ll reiterate my very thought from this blog post: I am not a fan of theories of dichotomies of thinking: they are often lazy and inaccurate. Having said that, the idea that we have a tendency towards big-picture or fine-detailed brain processing, directly correlated to the spacing of our cortical minicolumns and the distance our axonal connections spans, feels like a pretty good explanation of some of the individual differences that can be observed in the way we all approach and interpret the world.

*Spacing is regular within cortical area: the spacing within the occular cortex is regular, but different to that in visual cortex, which is again constituted of regularly spaced minicolumns, etc.

Citations

Casanova, M. & Trippe, J., (2009) Radial cytoarchitecture and patterns of cortical connectivity in autism, Philos. Trans. R Soc. Lond. B Biol. Sci. 364(1522): 1433-1436

Casanova, M., & Williams, E., (2010) Autism and dyslexia: A spectrum of cognitive styles as defined by minicolumnar morphometry, Medical Hypotheses, 74: 59–62

Casanova M., Buxhoeveden D., Switala A., Roy E., (2002a) Minicolumnar pathology in autism. Neurology 58: 428–432.
Casanova M., Buxhoeveden D., Cohen M., Switala A., Roy E., (2002b) Mini-columnar pathology in dyslexia, Ann Neurol 52: 108–110.
Eide, B., & Eide, F., (2011) The Dyslexic Advantage: Unlocking the hidden potential of the dyslexic brain. Hay House: London
Mountcastle, V., (1997) The columnar organisation of the neocortex, Brain, 120: 701–722
Opris, I., & Casanova, M., (2014) Prefrontal cortical minicolumn: from executive control to disrupted cognitive processing, Brain, 137: 1863–1875
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Importance of cortical spacing

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