Sexual Dimorphic Rightward Lateralization of Cerebral Sulcal Infolding in Cynomolgus Monkeys (Macaca fascicularis)

Abstract

Cerebral sulcal infolding exhibits unique species-related lateralization patterns. The present investigation aimed to characterize the asymmetric patterns of sulcal infolding in cynomolgus monkeys and their sexual dimorphism. Three-dimensional magnetic resonance (MR) images were acquired at 7-Tesla from the fixed brains of adult male (n = 5) and female (n = 5) monkeys. The gyrification index (GI) was estimated on MR images throughout the cerebral cortex (global-GI) or in the representative primary sulci (sulcal-GI). The global-GI did not differ between the sexes when the ipsilateral sides were compared. Although there was no sex difference in the sulcal-GI of the ipsilateral sides of any primary sulci, a significant right bias of the sulcal-GI was noted in the inferior rams of the arcuate sulcus and circular sulcus in males but not in females. Secondary sulcal emergence was examined to assess sulcal infolding asymmetry at the individual and population levels. Nonbiased asymmetric emergence was noted in the posterior supraprincipal dimple in both sexes and the rostral sulcus in females. Notably, the emergence of the superior postcentral dimple was significantly right-lateralized in females. The findings revealed right-biased sulcal infolding in male and female cynomolgus monkeys, although the lateralized cortical regions differed between the sexes.