Developmental trajectory of the corpus callosum from infancy to the juvenile stage: Comparative MRI between chimpanzees and humans

<div><p>How brains develop during early life is one of the most important topics in neuroscience because it underpins the neuronal functions that mature during this period. A comparison of the neurodevelopmental patterns among humans and nonhuman primates is essential to infer evolutional changes in neuroanatomy that account for higher-order brain functions, especially those specific to humans. The corpus callosum (CC) is the major white matter bundle that connects the cerebral hemispheres, and therefore, relates to a wide variety of neuronal functions. In humans, the CC area rapidly expands during infancy, followed by relatively slow changes. In chimpanzees, based on a cross-sectional study, slow changes in the CC area during the juvenile stage and later have also been reported. However, little is known about the developmental changes during infancy. A longitudinal study is also required to validate the previous cross-sectional observations about the chimpanzee CC. The present longitudinal study of magnetic resonance imaging scans demonstrates that the CC development in chimpanzees and humans is characterized by a rapid increase during infancy, followed by gradual increase during the juvenile stage. Several differences between the two species were also identified. First, there was a tendency toward a greater increase in the CC areas during infancy in humans. Second, there was a tendency toward a greater increase in the rostrum during the juvenile stage in chimpanzees. The rostral body is known to carry fibers between the bilateral prefrontal and premotor cortices, and is involved in behavior planning and control, verbal working memory, and number conception. The rostrum is known to carry fibers between the prefrontal cortices, and is involved in attention control. The interspecies differences in the developmental trajectories of the rostral body and the rostrum might be related to evolutional changes in the brain systems.</p></div

Sample characteristics of the corpus callosum areas relative to adult areas (normalized areas) in chimpanzees.

<p>Sample characteristics of the corpus callosum areas relative to adult areas (normalized areas) in chimpanzees.</p

Differences in normalized areas among CC subdivisions in humans.

<p>Differences in normalized areas among CC subdivisions in humans.</p

Differences in normalized areas among CC subdivisions in chimpanzees.

<p>Differences in normalized areas among CC subdivisions in chimpanzees.</p

Sample characteristics of the corpus callosum areas relative to adult areas (normalized areas) in humans.

<p>Sample characteristics of the corpus callosum areas relative to adult areas (normalized areas) in humans.</p

Evaluation of the normalized corpus callosum areas during development.

<p>Age-related changes in the total CC and the CC subdivisions relative to the adult areas during infancy and the juvenile stage are shown for chimpanzees (n = 4) and humans (n = 72). (A) total, (B) rostrum, (C) genu, (D) rostral body, (E) anterior midbody, (F) posterior midbody, (G) isthmus, and (H) splenium. The bar below the graphs indicates the developmental stage. The indicated developmental stages are infancy (open bar) and the juvenile stage (hatched bar).</p

Evaluation of the corpus callosum areas during development.

<p>Age-related changes in the total CC and the CC subdivisions during infancy and the juvenile stage are shown for chimpanzees (n = 4) and humans (n = 72). (A) total, (B) rostrum, (C) genu, (D) rostral body, (E) anterior midbody, (F) posterior midbody, (G) isthmus, and (H) splenium. The bar below the graphs indicates the developmental stage. The indicated developmental stages are infancy (open bar) and the juvenile stage (hatched bar).</p

Sample characteristics of the corpus callosum areas in humans.

<p>Sample characteristics of the corpus callosum areas in humans.</p

An ontogenetic series of the regional subdivisions of the chimpanzee corpus callosum from a midsagittal view.

<p>Regional subdivisions: 1 = rostrum (red); 2 = genu (green); 3 = rostral body (yellow); 4 = anterior midbody (blue); 5 = posterior midbody (magenta); 6 = isthmus (cyan); 7 = splenium (white). The bars below the figures indicate the developmental stage. The indicated developmental stages are infancy (open bar), the juvenile stage (hatched bar), and the adult stage (horizonal striped bar).</p

Regional subdivisions of the chimpanzee corpus callosum from a midsagittal view.

<p>The total CC midsagittal area was divided into seven equally spaced subdivisions: 1 = rostrum (red); 2 = genu (green); 3 = rostral body (yellow); 4 = anterior midbody (blue); 5 = posterior midbody (magenta); 6 = isthmus (cyan); 7 = splenium (white).</p