Searching For Selection
This response submitted by Vladimir on 8/8/97.
I also think that 0.5 mm thing requires some explanation but to build the whole theory on it seems a little over the edge to me. I'm neglecting Calvin's book for now and focusing on "Selectionism and the Brain" from 1994 edited by Sporns and Tononi. You should look at this book. It contains Olaf's article where he tries to define clearly neuronal groups, Tononi's article where he tries to define reentry, Reeke's article where he describes Darwin 3 and NOMAD (there is even a picture there) and many other interesting articles. I found especially interesting the article of Ramachandran about phantom limbs and anasognosia. I also found an interesting book from 1977 (before Edelman) by Valentino Braitenberg called "On Texture of Brains". Braitenberg tries to build a sketch of brain theory baised on anatomy. His ideas are very similar to mine (there is nothing new under the sun). He also talks about columns as neuronal groups but doesn't mention darwinian selection.
This brings me to a conclusion which is reinforced by the conversations I had with the people here. Edelman didn't invent 90% of the ideas he writes about. Many of them are even widely accepted. However the idea of selection from random variability formed during embryonic development is really original and can be the key to the whole thing. However, it is not the only possible key. Therefore, our primary task must be to test this idea. And to do this we need to define clearly neuronal groups and find the connection between them and columns. Some kind of columnar organization does exist though the columns aren't square as in pictures. Check out the work of Amiram Grinvald from Weizmann institute. He showed that the structures in V1 are not orientation columns but a kind of circles with fuzzy borders between regions sensitive to different angles.
However the spatiotemporal resolution of his method is not very high because he looks at changes in blood supply and oxihemoglobin concentration.
I looked at the paper by Rafael Yuste that I mentioned earlier. They really found some kind of cell groups very similar to Mountcastle's minicolumns in the cortex of neonatal rat. They showed that the cells were connected with GAP JUNCTIONS and fired together which caused influx of Ca. Therefore minicolums exist!!! The question is whether they really are what we think they are.
We should perform theoretical calculation based on data about number of cells in the cortex and their density to determine whether non-overlapping minicolumns can form primary repertoire large enough for Edelmanian process to take place. If not, we'll be forced to admit that the groups must be overlapping and this will really complicate the picture. If there is "Winner Take All" process we must determine how big is the region each winner represents. Is it macrocolumn? The whole map? or something else. This process is not that different from what is widely known as "lateral inhibition".We should look for selection. If there is no selection Edelmanism is not much better than Calvinism.
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The above was a post to a discussion forum I once hosted on an old Mac IICX.