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. 2015 Feb;156(2):252-62.
doi: 10.1002/ajpa.22646. Epub 2014 Oct 31.

Brain Organization of Gorillas Reflects Species Differences in Ecology

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Free PMC article

Brain Organization of Gorillas Reflects Species Differences in Ecology

Sarah K Barks et al. Am J Phys Anthropol. .
Free PMC article

Abstract

Gorillas include separate eastern (Gorilla beringei) and western (Gorilla gorilla) African species that diverged from each other approximately 2 million years ago. Although anatomical, genetic, behavioral, and socioecological differences have been noted among gorilla populations, little is known about variation in their brain structure. This study examines neuroanatomical variation between gorilla species using structural neuroimaging. Postmortem magnetic resonance images were obtained of brains from 18 captive western lowland gorillas (Gorilla gorilla gorilla), 15 wild mountain gorillas (Gorilla beringei beringei), and 3 Grauer's gorillas (Gorilla beringei graueri) (both wild and captive). Stereologic methods were used to measure volumes of brain structures, including left and right frontal lobe gray and white matter, temporal lobe gray and white matter, parietal and occipital lobes gray and white matter, insular gray matter, hippocampus, striatum, thalamus, each hemisphere and the vermis of the cerebellum, and the external and extreme capsules together with the claustrum. Among the species differences, the volumes of the hippocampus and cerebellum were significantly larger in G. gorilla than G. beringei. These anatomical differences may relate to divergent ecological adaptations of the two species. Specifically, G. gorilla engages in more arboreal locomotion and thus may rely more on cerebellar circuits. In addition, they tend to eat more fruit and have larger home ranges and consequently might depend more on spatial mapping functions of the hippocampus.

Keywords: cerebellum; hippocampus; primate brain evolution.

Figures

Figure 1
Figure 1
Example of measures of brain structure volume using stereology. Four coronal sections from a mountain gorilla brain are shown, anterior to posterior (see inset for level of each section). Structures shown, section 1: frontal gray (light yellow) and white matter (dark yellow). Section 2: parietal and occipital gray (light green) and white matter (dark green), temporal gray (light blue) and white matter (dark blue), hippocampus (tan). Section 3: parietal and occipital gray (light green) and white matter (dark green), thalamus (medium blue), insula gray (pink), external capsule/claustrum/extreme capsule (purple), striatum (orange), amygdala (red), temporal gray (light blue) and white matter (dark blue). Section 4: parietal and occipital gray (light green) and white matter (dark green), cerebellar vermis (dark yellow) and hemispheres (light yellow).
Figure 2
Figure 2
3-D “cloud” of all points measured in one mountain gorilla brain, representing the complete volume of all structures measured. “Claustrum area” refers to the region encompassing external capsule, claustrum, and extreme capsule.
Figure 3
Figure 3
PCA results. Blue circles represent G. gorilla; red squares represent G. b. beringei; red triangles represent G. b. graueri. A. Variance explained by each principal component (PC) for absolute volume of brain structures. B. PCA plot for absolute volumes, PCs 1 and 2. C. PCA plot for absolute volumes, PCs 3 and 4. D. Variance explained by each PC for proportional volume of brain structures. E. PCA plot for proportional volumes, PCs 1 and 2. F. PCA plot for proportional volumes, PCs 3 and 4.
Figure 4
Figure 4
Comparison of mean brain structure volumes in eastern (G.b.b., gray) and western gorillas (G.g.g., black), all subjects, assessed by Mann-Whitney pairwise tests. Error bars indicate +1 SD. Asterisks denote significant differences after correction for multiple comparisons, p < 0.05 (corrected α = 0.002). Bullets denote significant differences after correction for multiple comparisons, p < 0.10 (corrected α = 0.004). “Claustrum area” refers to the region encompassing external capsule, claustrum, and extreme capsule. A. Absolute volume (cm3). B. Proportional volume.
Figure 5
Figure 5
Comparison of mean brain structure volumes in eastern (G.b.b., gray) and western gorillas (G.g.g., black), adult subjects, assessed by Mann-Whitney pairwise tests. Error bars indicate +1 SD. Asterisks denote significant differences after correction for multiple comparisons (corrected α = 0.002). “Claustrum area” refers to the region encompassing external capsule, claustrum, and extreme capsule. A. Absolute volume (cm3). B. Proportional volume.

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