Tracking Development of the Corpus Callosum in Fetal and Early Postnatal Baboons Using Magnetic Resonance Imaging

Although the maturation of the corpus callosum (CC) can serve as a sensitive marker for normative antenatal and postnatal brain development, little is known about its development across this critical period. While high-resolution magnetic resonance imaging can provide an opportunity to examine normative brain development in humans, concerns remain over the exposure of developing fetuses to non-essential imaging. Nonhuman primates can provide a valuable model for normative brain maturation. Baboons share several important developmental characteristics with humans, including a highly orchestrated pattern of cerebral development. Developmental changes in total CC area and its subdivisions were examined across the antenatal (weeks 17 – 26 of 28 weeks total gestation) and early postnatal (to week 32) period in baboons (Papio hamadryas anubis). Thirteen fetal and sixteen infant baboons were studied using high-resolution MRI. During the period of primary gyrification, the total area of the CC increased by a magnitude of five. By postnatal week 32, the total CC area attained only 51% of the average adult area. CC subdivisions showed non-uniform increases in area, throughout development. The splenium showed the most maturation by postnatal week 32, attaining 55% of the average adult value. The subdivisions of the genu and anterior midbody showed the least maturation by postnatal week 32, attaining 50% and 49% of the average adult area. Thus, the CC of baboons shows continued growth past the postnatal period. These age-related changes in the developing baboon CC are consistent with the developmental course in humans

Conducting Publishable Research From Special Populations: Studying Children and Non-Human Primates with Undergraduate Research Assistants

Collecting publishable data with only undergraduate research assistants (RAs) is difficult; conducting research with young children or non-human primates (NHPs) adds a layer of difficulty, yet we have been able to successfully sustain and grow research programs in Developmental Psychology and primate Behavioral Neuroscience at Trinity University (TU), a primarily undergraduate institution (PUI) in San Antonio. We each have been conducting research for over 25 years, with most of that time at this type of institution, and have developed effective strategies for publishing articles with undergraduates in this environment

Cross-Sectional Analysis of the Association Between Age and Corpus Callosum Size in Chimpanzees (\u3cem\u3ePan troglodytes\u3c/em\u3e)

The CC is the major white matter tract connecting the cerebral hemispheres and provides for interhemispheric integration of sensory, motor and higher‐order cognitive information. The midsagittal area of the CC has been frequently used as a marker of brain development in humans. We report the first investigation into the development of the corpus callosum and its regional subdivisions in chimpanzees (Pan troglodytes). Magnetic resonance images were collected from 104 chimpanzees (female n = 63, male n = 41) ranging in age from 6 years (pre‐pubescent period) to 54 years (old age). Sustained linear growth was observed in the area of the CC subdivision of the genu; areas of the posterior midbody and anterior midbody displayed nonlinear growth during development. After adjusting for total brain size, we observed linear growth trajectories of the total CC and CC subdivisions of the genu, posterior midbody, isthmus and splenium, and nonlinear growth trajectories of the rostral body and anterior midbody. These developmental patterns are similar to the development of the CC in humans. As the growth curves of the CC mirrors growth seen in the percentage of white matter in humans, our results suggest chimpanzees show continued white matter development in regions related to cognitive development

Hand Preference for Tool-Use in Capuchin Monkeys (\u3cem\u3eCebus apella\u3c/em\u3e) is Associated with Asymmetry of the Primary Motor Cortex

Skilled motor actions are associated with handedness and neuroanatomical specializations in humans. Recent reports have documented similar neuroanatomical asymmetries and their relationship to hand preference in some nonhuman primate species, including chimpanzees and capuchin monkeys. We investigated whether capuchins displayed significant hand preferences for a tool use task and whether such preferences were associated with motor-processing regions of the brain. Handedness data on a dipping tool-use task and high-resolution 3T MRI scans were collected from 15 monkeys. Capuchins displayed a significant group-level left-hand preference for this type of tool use, and handedness was associated with asymmetry of the primary motor cortex. Left-hand preferent individuals displayed a deeper central sulcus in the right hemisphere. Our results suggest that capuchins show an underlying right-hemisphere bias for skilled movement

Age-Related Differences in Corpus Callosum Area of Capuchin Monkeys

Capuchin monkeys (Cebus apella) are New World primates with relatively large brains for their body size. The developmental trajectories of several brain regions-including cortical white matter, frontal lobe white matter, and basal ganglia nuclei-are similar to humans. Additionally, capuchins have independently evolved several behavioral and anatomical characteristics in common with humans and chimpanzees-including complex manipulative abilities, use of tools, and the use of precision grips-making them interesting species for studies of comparative brain morphology and organization. Here, we report the first investigation into the development of the corpus callosum (CC) and its regional subdivisions in capuchins. CC development was quantified using high-resolution structural magnetic resonance imaging (MRI) images from 39 socially reared subjects (male n=22; female n=18) ranging in age from 4 days (infancy) to 20 years (middle adulthood). The total area of the CC and the subdivisions of the genu, rostral midbody, medial midbody, caudal midbody, and splenium were traced from the midsagittal section. Total CC area displayed significant differences across this time span and was best explained by quadratic growth. Sustained linear growth was observed in the subdivisions of the genu, rostral midbody, and splenium; sustained quadratic growth was seen in the subdivision of the medial midbody. Differences in growth were not detected in the subdivision of the caudal midbody. Females had a larger raw area of the total CC and of the medial midbody and caudal midbody throughout the lifespan. Our results indicate that capuchins show continued white matter development beyond adolescence in regions related to cognitive and motor development

The Effect of Body Region on Hair Cortisol Concentration in Common Marmosets (\u3cem\u3eCallithrix jacchus\u3c/em\u3e)

Common marmosets (Callithrix jacchus) are a valuable research model for the study of neuroscience and the biologic impact of aging due to their adaptivity, physiologic characteristics, and ease of handling for experimental manipulations. Quantification of cortisol in hair provides a noninvasive, retrospective biomarker of hypothalamics-pituitary-adrenal (HPA) axis activity and information on animal wellbeing, including responses to environmental and social stimuli. To obtain valid and reliable measurements of long-term HPA activity, we investigated the variability of cortisol concentration in the hair depending on the body region of marmosets. Hair was collected from the back and tail of 9 adult common marmosets during annual health screenings (male n = 3; female n = 6) and these samples were analyzed for cortisol via methanol extraction and enzyme immunoassay. We found that hair cortisol concentration differed between the tail and back regions, with the tail samples having a significantly higher cortisol concentration. These results indicate intraindividual and interindividual comparisons of hair cortisol concentration should use hair obtained from the same body region in marmosets

Corpus Callosal Microstructure Influences Intermanual Transfer in Chimpanzees

Learning a new motor skill with one hand typically results in performance improvements in the alternate hand. The neural substrates involved with this skill acquisition are poorly understood. We combined behavioral testing and non-invasive brain imaging to study how the organization of the corpus callosum was related to intermanual transfer performance in chimpanzees. Fifty-three chimpanzees were tested for intermanual transfer of learning using a bent-wire task. Magnetic resonance and diffusion tensor images were collected from 39 of these subjects. The dominant hand showed greater performance benefits than the nondominant hand. Further, performance was associated with structural integrity of the motor and sensory regions of the CC. Subjects with better intermanual transfer of learning had lower fractional anisotropy values. The results are consistent with the callosal access model of motor programming

Myelin Characteristics of the Corpus Callosum in Capuchin Monkeys (\u3cem\u3eSapajus\u3c/em\u3e [\u3cem\u3eCebus\u3c/em\u3e] \u3cem\u3eapella\u3c/em\u3e) Across the Lifespan

The midsagittal area of the corpus callosum (CC) is frequently studied in relation to brain development, connectivity, and function. Here we quantify myelin characteristics from electron microscopy to understand more fully differential patterns of white matter development occurring within the CC. We subdivided midsagittal regions of the CC into: I—rostrum and genu, II—rostral body, III—anterior midbody, IV—posterior midbody, and V—isthmus and splenium. The sample represented capuchin monkeys ranging in age from 2 weeks to 35 years (Sapajus [Cebus] apella, n = 8). Measurements of myelin thickness, myelin fraction, and g-ratio were obtained in a systematic random fashion. We hypothesized there would be a period of rapid myelin growth within the CC in early development. Using a locally weighted regression analysis (LOESS), we found regional differences in myelin characteristics, with posterior regions showing more rapid increases in myelin thickness and sharper decreases in g-ratio in early development. The most anterior region showed the most sustained growth in myelin thickness. For all regions over the lifespan, myelin fraction increased, plateaued, and decreased. These results suggest differential patterns of nonlinear myelin growth occur early in development and well into adulthood in the CC of capuchin monkeys

Performance Asymmetries in Tool Use are Associated with Corpus Callosum Integrity in Chimpanzees (\u3cem\u3ePan troglodytes\u3c/em\u3e): A Diffusion Tensor Imaging Study

The authors examined the relationship of corpus callosum (CC) morphology and organization to hand preference and performance on a motor skill task in chimpanzees. Handedness was assessed using a complex tool use task that simulated termite fishing. Chimpanzees were initially allowed to perform the task wherein they could choose which hand to use (preference measure), then they were required to complete trials using each hand (performance measure). Two measures were used to assess the CC: midsagittal area obtained from in vivo magnetic resonance images and density of transcallosal connections as determined by fractional anisotropy values obtained from diffusion tensor imaging. The authors hypothesized that chimpanzees would perform better on their preferred hand compared to the nonpreferred hand, and that strength of behavioral lateralization (rather the direction) on this task would be negatively correlated to regions of the CC involved in motor processing. Results indicate that the preferred hand was the most adept hand. Performance asymmetries correlated with fractional anisotropy measures but not area measures of the CC