Abstract
The insula has been classically divided into vast granular, dysgranular and agranular sectors. Over the years, several distinct studies proposed subdivisions of these sectors, with however no consensus. We recently proposed a cyto- and myelo-architectonic partition in which each sector contained sharply delimited areas (Evrard et al. 2014 J Comp Neurol 522: 64-97). Some of these areas were further divided into distinct subareas with obvious functional implications. Here, we examined the spatial relationship between architectonic boundaries and tract-tracing labeling in the insula in the macaque monkey. Injections of neuronal tracers in distinct areas of the prefrontal or anterior cingulate cortices produced heterogeneous and discontinuous patterns of anterograde and retrograde labeling in the insula. These patterns were made of sharply delimited patches forming anteroposterior stripes across consecutive coronal sections. While the overall pattern of labeling varied with the injection site, the patches systematically coincided with specific architectonic subareas, particularly in the dysgranular insula. This unequivocally validates our prior architectonic partition and strongly supports the idea of a refined modular Bauplan of the primate insula. This modular organization may underlie a serial stream of integration of interoception with ‘self-agency’ and ‘social’ activities across distinct insulo-prefrontal processing units that need to be explored.
Competing Interest Statement
The authors have declared no competing interest.
Abbreviations
- BDA
- Biotinylated dextran amine
- CTb
- Cholera toxin subunit B
- FR
- Fluororuby
- Iai
- intermediate agranular area of the insula
- Ial
- lateral agranular area of the insula
- Iam
- medial agranular area of the insula
- Iap1-2
- posterior agranular area of the insula, subareas 1 and 2
- Iapl
- posterior lateral agranular area of the insula
- Iapm
- posterior medial agranular area of the insula
- Idd1-5
- dorsal dysgranular area of the insula, subareas 1 to 5
- Idfa
- anterior (granular) area of the dorsal fundus of the insula
- Idfp
- posterior (granular) area of the dorsal fundus of the insula
- Idm1-3
- mound dysgranular area of the insula, subareas 1 to 3
- Idv1-2
- ventral dysgranular area of the insula, subareas 1 and 2
- ILS
- Inferior limiting sulcus of the insula
- Ivfa
- anterior (agranular) area of the ventral fundus of the insula
- Ivfp
- posterior (dysgranular) area of the ventral fundus of the insula
- LY
- Lucifer yellow
- SLS
- superior limiting sulcus of the insula