I write this after I read Eric Kandel's lecture at the Heineken prize 2000, because I found the level of misunderstanding that it shows in the discussion of individuality quite shocking when it comes from a noble laureate.
I always write that neuroscientists know that the connectivity inside the cortex varies randomly across individuals (e.g. here and here), but in the case of Kandel I am not sure any more. That is because of the way he discusses "structural changes and the biological basis of individuality". In the end of the section he writes (p. 48 (26 in the PDF numbering)):
The finding of the anatomical changes are potentially significant for understanding the biological basis of individuality for they suggest that even identical twins that share an identical genome are likely to have somewhat different brains because they are certain to have somewhat different life experiences.That suggests very strongly that Kandel believes that without the "anatomical changes" which are caused by "different life experiences", identical twins will be really identical. Of course, even between identical twins the connectivity of the cortex will vary randomly. We know that from non-human mammals, where it is possible to actually compare the connectivity. If it was identical between genetically identical animals, at any stage of their development, we would have already been able to find the circuitry.
I can think of two explanations for what Kandel writes:
Thus, the unique functions of the hippocampus had to arise not so much from the intrinsic properties of pyramidal neurons but from the pattern of functional interconnections of these cells, and how those interconnections are affected by learning.Thus he doesn't completely ignore patterns of connectivity ("functional interconnection"). It is therefore not obvious to me which of the explanations is the correct explanation. Either case, it is a clear demonstration of deep misunderstanding of the mammalian system.
In the section about "Place cells as a test of models of memory in the hippocampus" (p. 48 (26 in the PDF numbering)), Kandel writes:
The hippocampal pyramidal cells are place cells.Hey? And they don't do anything else? That certainly the way the sentence is written. Kandel explains what he means in the following sentence:
They fire when an animal occupies a specific area in its environment (this area is called the place field for a specific cell).But of course they also fire when the animal is in other locations, just much less frequently. That, however, is not something that you can read in the text, you have to already know it. The next sentence is very slightly better:
Any pyramidal cell can function as a place cell and, in any given environment, about half of the cells in the hippocampus function as place cells.But you have either to know already about the hippocampus, or to be an extremely alert reader, to realize that it leaves open the possibility that the pyramidal cells may also do other things than just firing when the animal is in the right place. It gives a very strong impression that Kandel himself believes that this firing is the only significant activity of the pyramidal cells.
22 Sep 2003