Ok, first things first. I'm going to have to break this up into several parts. I've tried doing figuring out how to shrink it to one concise post, but haven't found out how. There are prerequisites that must be explained before we get to what I was referring to as Esparanto's Apple.
The first thing that must be made clear is the modern conception of memory and concepts in the brain. It is a theory that Donald Hebb put forward in 1949 and according to Calvin is
the way of looking at it.
Hebb said that concepts were implemented by a characteristic firing pattern in a small group of cortical neurons, which he dubbed a "cell-assembly." To recall someone's name, you needed to recreate that musical spatiotemporal firing pattern. But, because of the way that a long term memory survived episodes such as coma and seizure, it had to be a spatial-only pattern like washboarded ruts in well worn roads, something that didn't require ongoing neural activity such as impulses firing away. (The washboarded rut idea is that at a certain speed, the ruts vibrate the hell out of your car. There is another pattern in the ruts that would do the same for a truck. It's an overlay of patterns idea.)
These ruts are conceived somewhat like the grooves of a phonograph record. It's all about spatiotemporal firings being recorded in a strictly spacial manner. This is how they are able to survive coma and seizure. He speaks of resonance quite a bit. Kind of like the 'burned in' effects of an epileptic seizure. The smell of chocolate or whatever precursor there may be. Nowadays, it is more in style to use terms such as "chaotic attractor" to emphasize the way pattern variations conform to a standard. (I'm not entirely sure about the mechanics of this chaotic attractor. It sounds familiar and perhaps I've come across it in the past, but the details are eluding me and the book doesn't clarify. Maybe you could shed some light on it. Heard of it?)
Ok, pretty basic so far, right? I'm sure nothing new has been introduced to you here.
Now, Calvin gives credit to J.W.S. Pringle, a contemporary of Hebb, for the idea of a 'plainchant' chorus. For a concept, memory, whatever to achieve any type of cohesion, force, clarity it must be shouted out by a large number of neurons (cell-assemblies) simultaneously. The more that shout the praises of a concept the more powerful the concept is within your mind. It also acts to solidify a standard pattern from variable patterns. This is a key concept in thought. Single neurons are messy and sloppy. It takes many working in unison and in parallel to achieve the clarity of thought which we apparently have.
Ok, next, he brings in the topic of pyramdal neurons. These are tall with triangular-shaped bodies and are the most numerous of the cortical neurons. Input: They have a large dendritic tree ascending up towards the cortical surface before breaking into finer branches. Output: A single axon which branches eventually as well. Some of the branches end up quite close, some far away.
Ok, there are two types of pyramidal neurons. There are those with their cell bodies in the upper layer of cortex and those with their cell bodies in a lower layer.
Here's a diagram. Now, these deep-seated neurons are neurons of a different sort and I won't be discussing them. But, the surface neurons have a curious tendency. Their axons (which drift to the side, not up or down) tend to skip neurons. They tend to make synaptic connections at 0.5, 1.0, 1.5 mm distance. Now, since neurons have the same average gap length, there's a good chance that they will have reciprocal connections. I.e. A will excite B and B will excite A back. This allows neurons to fire simultaneously without being directly adjacent to each other. He gives this explanation why it works this way rather than them chasing their tails.
"Many models of coupled oscillators exhibit such entrainment; it was first reported in 1665 by the Danish physicist Christian Huygens, who noticed that two pendulum clocks sitting on the same shelf would synchronize their ticks via vibrations within a half hour after being started at different times. Fireflies do the same thing much more quickly; whole trees full of fireflies can be observed flashing in synchrony."
So, one neuron may fire (along with it's partners about the area) then it's neighbor may fire (along with it's partners). With this mechanism, the plainchant choirs begin to form.
In the above diagram, there is also mention made of microcolumns. Groups of 100 neurons or so that share a common dendritic bush. For effects and purposes, these can be considered to be one neuron. Now,
here's another diagram that shows a hexagonal structure made up of 300 or so microcolumns. This is the essence of this idea of thought. This hexagonal structure is like a 300 key piano. Inside it, all sorts of tunes can be played out. The hex is about 0.5 mm in width, so this linking capacity that the neurons show would connect this hex with other hex's nearby. Therefore, if a hex begins to play a tune, it can reach out to neighbouring hexes and begin to acquire territory. In this way, the chorus begins.
An explanation for why the 0.5 mm hex.
"So how many keys does the cortical piano have? Well, the largest collection of active nodes (from all arrays taken together) that has no redundancies (just one member of each active array) could be no larger than a hexagon 0.5 mm across (the corresponding points -- say the upper left corners -- of a mosaic of hexagonal tiles are always connected by triangular arrays)."
Are you following me? I think I've got this part completed rather well. I think I'll finish this post here and begin with the next step in a later post.
One more idea. This idea of hex's doesn't necessarily mean that this is
the only hex that contains any particular neuron. There can be many overlapping hexes that take part in different functions, concepts, etc... Get me?
Coming up next. Darwinian competition for cortical territory.
