During our analysis, we detected the following four types of concordance: (a) a particular NB area corresponds with a single HCP area; (b) a particular NB area corresponds with a set of HCP areas; (c) a particular HCP area corresponds with a set of NB areas, and (d) a set of NB areas corresponds with a set of HCP areas (but further concordances within these two groups are uncertain). The various entities showing concordance are collectively denoted as loci of concordance.
The results of our analysis are presented in Table 1. All loci of concordances found are collectively colored orange in Figs. 5, 6, 7, 8).
Table 1 Loci of Concordance in Map NB and Map HCPThe frontal lobeAs has already been mentioned, we do not trust the correctness of the parcellation of the frontal lobe, as shown in Nieuwenhuys and Broere (2023: Figs. 4A, B) anymore. In these figures, the areas 38–40 and 42–43 are extraordinarily wide, with spatial consequences for the areas located in the remainder of the lobe. A preliminary reanalysis of our material, including the study of Hopf (1956), indicates that the antero–posterior dimensions of the areas mentioned are much smaller, and that area 40 is not only smaller, but also forms part of area 38. Because of these discrepancies, we decided to replace the lateral and superior views of the frontal lobe in our original 3D parcellation of the frontal lobe, by 2D maps, reflecting our new insights (Fig. 5A, B). The NB areas 38 + 40, 39, 42 and 43 in these new maps are all heavily myelinated, and are obviously collectively concordant with the likewise heavily myelinated HCP area 4. A phenomenon, described by Vogt and Vogt (1919) and Hopf (1956), viz. that in the frontal lobe the overall density of the myelin decreases stepwise from the precentral (motor) cortex to the frontal pole, could be confirmed by Glasser et al. (2016a, Fig. 10B of the Supplemental Neuroanatomical Results). It may be added that the areas that receive the large sensory projections (somatosensory, auditory, visual) are also heavily myelinated, and that the myelination decreases stepwise from all of these areas.
Several of the areas, observed on the lateral aspect of the frontal lobe, including NB areas 36, 37, 38 + 40, 39 and 42, and their HCP concordances (cf. Table 1) extend, via the superior aspect (Figs. 5B, 6B), over the medial aspect of the frontal lobe (Figs. 7A, 8A). The remaining concordances detected on the medial aspect of the frontal lobe are mainly confined to the zone adjacent to the corpus callosum (Figs. 7A, 8A).
It has already been mentioned that the human neocortex contains, apart from the primary sensory and motor areas, several other densely myelinated loci, each consisting of one or more areas. One of these dark loci is found in the orbitofrontal cortex, and consists of NB areas 60 + 61 (Fig. 4A) and HCP area 47m (Fig. 4B). This cluster facilitated the identification of some adjacent areas, viz. NB areas 62 and 63 and HCP areas 13l and 47s.
Two loci of concordance occupy the medial part of the orbitofrontal cortex. These loci are represented by the HCP areas OFC and pOFC (Fig. 5B). HCP area OFC (Fig. 8A, B) is concordant with the set of NB areas 1, 4, 5, 6, 8 (Fig. 7A, B), whereas HCP area pOFC (Fig. 8B) is concordant with NB area 66 (Fig. 7B). Note that HCP area OFC is located in a region where the MRI-based parcellation is inaccurate because of MRI signal loss. The olfactory sulcus (Figs. 2, 3) occupies a central position in the concordant NB loci 1 + 4 + 5 + 6 + 8 and HCP locus OFC.
A large number of concordances could be determined in the parietal lobe. The postcentral gyrus, bounded anteriorly by the central sulcus and posteriorly by the postcentral sulcus (Figs. 2, 3), contains four elongated, strip-like areas, the NB areas 67, 69, 70 and 71 (Fig. 5A, B), which are evidently concordant with the HCP areas 3a, 3b, 1 and 2, respectively (Fig. 6A, B). The superior parietal lobule, which is partly separated from the inferior parietal lobule by the intraparietal sulcus (Fig. 2), contains a heavily myelinated locus, consisting of the NB areas 86 and 87 (Fig. 5A, B), concordant with the HCP areas LIPd + MIP and LIPv, respectively (Fig. 6A, B). Some of the areas in the inferior parietal lobule show one-to-one concordances in the two maps, as e.g. NB area 68 (Fig. 5A) with HCP area OP4 (Fig. 6A), and NB area 72 (Fig. 5A) with HCP area PFop (Fig. 6A), but by far most of the other areas in this lobule, and all remaining areas in the superior parietal lobule, show one-to-two or one-to-many concordances. Here, we confine ourselves to two examples: NB area 83 (Fig. 5A, B) corresponds with HCP areas VIP + 7AM + PCV (Figs. 6A, B), and NB area 90 (Fig. 5A, B) corresponds with HCP areas PGi + PGs + PGp + TPOJ2 + TPOJ3 (Fig. 6A, B). Note, however, that VIP has a substantially higher myelin content than 7AM and PCV in the MRI-based myelin maps. On the medial side of the parietal lobe, the superior parietal lobule and the precuneus are occupied by medial extensions of the NB areas 75, 83 and 85 (Fig. 7A) and their concordant composite HCP loci (Fig. 8A). It is noteworthy that HCP area POS2 is substantially more heavily myelinated than other portions of NB area 85 (Glasser and Van Essen 2011) and this large hotspot of heavier myelination appears to have been missed by the classical myeloarchitectonic maps, perhaps because the parieto-occipital sulcus was the border zone between several of the maps that confined themselves to the parietal or occipital lobes (Vogt 1911; Lungwitz 1937; Batsch 1956) but was itself perhaps not studied intensively. Finally, the pericallosal NB areas 91, 92 and 93 (Fig. 7A), which are more heavily myelinated than their adjacent areas, are collectively concordant with HCP area RSC (Fig. 8A).
In the insular lobe six concordances could be detected: NB areas 97, 98, 99, 100, 101 and 102 (Fig. 5A) correspond with HCP areas AAJC, AVI, MI, Pol2, Pol1 and 52, respectively (Fig. 6A).
The occipital lobeAs is well known, Brodmann (1909) divided the human occipital cortex into three concentrically arranged areas, the area striata (BA17), area occipitalis (BA18) and area preoccipitalis (BA19). Areas BA17 and BA18 are in all classical mapping studies of the human cortex recognized as distinct entities (cf. Braak 1980); hence, NB included these areas in their map (Fig. 7A, B). They are obviously concordant with the HCP areas V1 and V2 (Figs. 6B; 8A, B). Area 17BA/V1 is found within the calcarine sulcus (Fig. 2). Glasser et al. (2016a, Fig. 2B of the Supplemental Neuroanatomical Results) found that both of these areas are heavily myelinated, area V1 even stronger than V2. Contrary to areas BA17 and BA18, area BA19 has appeared to be heterogeneous. Lungwitz (1937), who studied its myeloarchitecture, divided it into no less than 17 different areas. These are included in our NB map, where they are numbered 103–119 (Figs. 5A, B and 7A, B) They correspond collectively with the 13 HCP areas V3, V3A, V3B, V4, V4t, V6, V6A, V7, V8, VMV1, VMV2, VMV3 and VVC (Figs. 6A, B and 8A, B). We failed, however, to detect concordances between the individual areas of these two parcellations, except for NB area 111 (Fig. 7A), which corresponds topologically with HCP area V6 (Fig. 8A).
The temporal lobeThe parcellation of the temporal lobe of the NB map (Figs. 5A and 7A, B), appeared to be so different from that of the HCP map (Figs. 6A and 8A, B), that we succeeded in finding only two loci of concordance in these two maps, one in the posterolateral temporal region, the other in the planum temporale. The posterolateral locus is composed of the NB areas 171 + 172 (Fig. 5A), and of the HCP areas MT + MST (Fig. 6A). The areas forming this locus are characterized by a very high myelin content. The likewise very heavily myelinated locus in the planum temporale, is formed by the primary auditory cortex, which includes in the NB map no less than 14 areas: 145–157 + 161 (Fig. 5A). This cortex is in the HCP map represented by 5 areas: R1, A1, LBelt, PBelt and MBelt (Fig. 6A).
In total, we detected 61 loci of concordance, 33 of type a, 13 of type b, 12 of type c, and 3 of type d. All concordances of type a (i.e. one-to-one), and all concordances, primarily based on heavy myelination, are presented in Figs. 5, 6, 7, 8 in dark orange; all remaining concordances in light orange.
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