Brain organization of gorillas reflects species differences in ecology.

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.

Cyclic changes in hormonal, physical, behavioral, and linguistic measures in a female lowland gorilla.

Since 1972, Koko, a captive-born female lowland gorilla, has been the subject of longitudinal linguistic and behavioral research. Data on behavioral and physical concomitants of Koko's estrous cycle have been gathered since her cycles began at the age of 5 years, 9 months. This study presents evidence of endocrinological influence on cognitive functioning: It demonstrates that frequency of sign-language use by Koko is greater in the follicular phase of her reproductive cycle. This finding supports an earlier report on Koko and is in agreement with recent studies correlating human menstrual-cycle phases with patterns of manual sequencing and verbal fluency. This study also confirms that nonlaboratory hormone tests designed for human female urine samples appear to be useful for detecting luteinizing hormone (LH) in gorilla urine and establishes the applicability of such tests for determining pregnanediol-3-glucuronide (PdG) levels in gorilla urine. Analyses of preliminary test results indicate that these enzyme immunoassay (EIA) tests match earlier radioimmunoassay (RIA) findings on the relationship between reproductive hormones and variables such as genital swelling and proceptivity in female gorillas.