# Is the ordering of Brodmann areas arbitrary?

A single Brodmann area is defined based off cellular composition. Are the Brodmann areas ordinal, and if so for what reason? (e.g. is there something that makes Brodmann area 1 the "first one", and area 2 the "second one"?)

• Why do you assume that there is any meaningful ordinal relation at all? (Cardinal) Numbering can be a convenient way of naming and the sequence may just follow whatever sequence was convenient for Brodmann, even if it has no useful meaning afterwards. And I've never heard ordinal numbers applied to Brodmann's areas, only the cardinal numbering. – Livius Mar 6 '16 at 4:05
• I have no idea if the sequence is arbitrary or not, hence why I'm asking the question. – RECURSIVE FARTS Mar 6 '16 at 4:12
• I also just want to add on, If Brodmann areas are rooted in cytology, I don't see how they could express the cardinality of something in the brain--it would imply some sort of a numerical relation. So I guess the question is: are they being used in a nominal sense or a ordinal sense? Lemme know if I'm missing something here though :) – RECURSIVE FARTS Mar 6 '16 at 4:19
• The question you're asking presupposes that the sequence is not arbitrary ("what makes..."). If you don't wan that assumption, then the question should be "Is there something that that makes ...., and " if so, what is it?" or something similar. In linguistic use, "cardinal numbers" are simply one, two, three, etc. (what you refer to as nominal) and "ordinal numbers" are first, second, third, etc. This is somewhat different from (albeit deeply related to) the mathematical notion of cardinality of sets, which include such things as $\aleph_0$. – Livius Mar 6 '16 at 4:25
• Sure, I thought you were using cardinal in a set-theoretic sense, I'll update the title to be a bit more clear. – RECURSIVE FARTS Mar 6 '16 at 4:27

## 1 Answer

The place to find this answer is of course Brodmann's original 1909 manuscript Vergleichende Lokalisationslehre der Großhirnrinde: in ihren Prinzipien dargestellt auf Grund des Zellenbaues available here in German or here in English (Brodmann's Localisation in the Cerebral Cortex: The Principles of Comparative Localisation in the Cerebral Cortex Based on Cytoarchitectonics).

The English version is unfortunately not open access (and I don't have the inclination to pay US\$90 for it) and the German version is a scanned copy of the original printing, so there's no easy way to search the text without reading all of it. However, skimming through it, I see that the description of the areas (which he calls Felder, lit. 'fields') begins in Kapitel IV (Chapter 4), page 130. He mentions that this work is largely an extension of his previous 1907 work, but beyond that there doesn't appear to be any mention of why he choose his numbering, at least not that I could find with a quick skim. It appears though that he choose a more or less arbitrary starting point and worked more or less counter clockwise from there, with a few small exceptions.

Elsewhere in the manuscript, Brodmann discusses the division of the cortex into larger homologous regions in both humans and other mammals (p. 129), and it's clear from the description of the areas that they are not divided up based on any study of homology. For example, he mentions that the regio postcentralis (lat. "post central region") is divided up into the cytoarchitectural areas 1, 2, 3 and 43 (pp. 130--132). The regions appear to correspond loosely with our modern notion of "lobes", but tend to be somewhat smaller (for example, there are additional subdivisions near the central sulcus).