Subcortical neuroanatomical hypotheses

Dataset characteristics relative to the social grade.

In red: social tolerance grade 1, orange: grade 2, olive: grade 3, and green: grade 4. (A) Social tolerance grade distribution, where grade 1 is overrepresented due to the prevalence of Macaca mulatta in laboratories. (B) Sex distribution: There was a significant imbalance in the sample, with females outnumbering males (2:1 ratio). (C) Husbandry distribution of the individuals (enclosed and semi-free ranging conditions) (D) Age distribution: The cohort had a relatively even age distribution with a notable peak in the 20s. (E) The frozen status distribution. (F) Total brain volume distribution, excluding the myelencephalon and cerebellum due to variation in their preservation.

Model predictors of the amygdala and hippocampus, and volume predictions across social tolerance grades.

First row (A–D): Model predictors and responses for amygdala volume. The volume ratio is calculated as the amygdala volume divided by the total brain volume (excluding the myelencephalon and cerebellum). (A) Distribution of amygdala volume ratios across social tolerance grades. (B) Distribution of amygdala volume ratios by sex. (C) Distribution of amygdala volume ratios by husbandry condition (enclosed vs. semi-free). (D) Distribution of amygdala volume ratios by the frozen status. (E) Distribution of amygdala volume ratios by age. Second row (F–J): Model predictors and responses for hippocampal volume. The volume ratio is calculated as the hippocampal volume divided by the total brain volume (excluding the myelencephalon and cerebellum). (F) Distribution of hippocampal volume ratios across social tolerance grades. (G) Distribution of hippocampal volume ratios by sex. (H) Distribution of hippocampal volume ratios by husbandry condition (enclosed vs. semi-free). (I) Distribution of hippocampal volume ratios by the frozen status. (I) Distribution of hippocampal volume ratios by age.

Parameters of the model.

(A) Parameters of the model for the amygdala volume. (B) Parameters of the model for the hippocampal volume. SG [x]: Social Grade [x] vs Social Grade [1]; SG[x]:Age (10 years): Social Grade-Age interaction.

Volume predictions across social tolerance grades of the amygdala and hippocampus.

All panels represent the predictions of the multivariate Bayesian linear model, where all the variables are kept constant (including total brain volumes) in order to represent the effect of age only on the volume of amygdala and hippocampus. First row (A–D): Predicted amygdala volume across social tolerance grades over the lifespan. (A) Predicted amygdala volume as a function of age for grade 1 individuals. (B) Predicted amygdala volume as a function of age for grade 2 individuals. (C) Predicted amygdala volume as a function of age for grade 3 individuals. (D) Predicted amygdala volume as a function of age for grade 4 individuals. Second row (E–H): Predicted hippocampal volume across social tolerance grades over the lifespan. (E) Predicted hippocampal volume as a function of age for grade 1 individuals. (F) Predicted hippocampal volume as a function of age for grade 2 individuals. (G) Predicted hippocampal volume as a function of age for grade 3 individuals. (H) Predicted hippocampal volume as a function of age for grade 4 individuals.

Sequence of dissection steps and MRI acquisition.

(A) Craniotomy step: Position of the cadaver and cut site. (B) Steps of scalp and skull removal using a Dremel tool® associated with a flex shaft rotary tool. (C) View of the skull after skull and dura removal. (D) Extraction and formaldehyde fixation of the brain. Right lateral view of the brain after a 7 day-formaldehyde-fixation. (E) SARM Regions (SARM2) and 3D MRI acquisition with atlas (bottom right). Amygdala (purple) (Hartig et al., 2021).

Set of photographs of the preparation of the fixed brain for MRI acquisitions.

(A) Air bubble removal stages in a vacuum chamber. The brain is immersed in FluorinertTM FC-770 and held in position by the aquarium foam squares. The container is placed in a receptacle to catch any FluorinertTM FC-770 that may spill out of the container during the procedure; (B) Placement of the aquarium foam squares inside the container of brain immersed in FluorinertTM FC-770 and sealed with parafilm; (C) Placement of the container with a lift foam square to contain the residual air bubble in the top third of the container; (D) Placement of the container in the MRI antenna.

Species and data collection centers in the dataset

Necessary materials for NHP brain extraction– name and description.

Information relating to the acquisition of anatomical MRI images and the procedures for fixing and preserving post-mortem samples according to the different centers.