Nishio Monami, Liu Xingyu, Mackey Allyson P, Arcaro Michael J
Department of Psychology, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
bioRxiv. 2025 Feb 6:2025.02.06.636851. doi: 10.1101/2025.02.06.636851.
Myelination is fundamental to brain function, enabling rapid neural communication and supporting neuroplasticity throughout the lifespan. While hierarchical patterns of myelin maturation across the cortical surface are well-documented in humans, it remains unclear which features reflect evolutionarily conserved developmental processes versus human-characteristic adaptations. Moreover, the laminar development of myelin across the primate cortical surface, which shapes hierarchies and supports functions ranging from sensory integration to network communication, has been largely unexplored. Using neuroimaging to measure the T1-weighted/T2-weighted ratio in tissue contrast as a proxy for myelin content, we systematically compared depth-dependent trajectories of myelination across the cortical surface in humans and macaques. We identified a conserved "inside-out" pattern, with deeper layers exhibiting steeper increases in myelination and earlier plateaus than superficial layers. This depth-dependent organization followed a hierarchical gradient across the cortical surface, progressing from early maturation in sensorimotor regions to prolonged development in association areas. Humans exhibited a markedly extended timeline of myelination across both cortical regions and depths compared to macaques, allowing for prolonged postnatal plasticity across the entire cortical hierarchy - from sensory and motor processing to higher-order association networks. This extended potential for plasticity may facilitate the shaping of cortical circuits through postnatal experience in ways that support human-characteristic perceptual and cognitive capabilities.
髓鞘形成对于大脑功能至关重要，它能实现快速的神经通讯，并在整个生命周期中支持神经可塑性。虽然人类大脑皮质表面髓鞘成熟的分层模式已有充分记录，但尚不清楚哪些特征反映了进化上保守的发育过程，哪些是人类特有的适应性特征。此外，灵长类动物皮质表面髓鞘的分层发育塑造了层级结构，并支持从感觉整合到网络通讯等多种功能，但这方面在很大程度上尚未得到探索。我们利用神经成像技术测量组织对比度中的T1加权/T2加权比值，以此作为髓鞘含量的替代指标，系统地比较了人类和猕猴皮质表面髓鞘形成随深度变化的轨迹。我们发现了一种保守的“由内向外”模式，即深层的髓鞘形成增加更为陡峭，且比浅层更早达到平稳期。这种随深度变化的组织模式在皮质表面遵循分层梯度，从感觉运动区域的早期成熟发展到联合区域的延长发育。与猕猴相比，人类在皮质区域和深度上的髓鞘形成时间线显著延长，这使得从感觉和运动处理到高阶联合网络的整个皮质层级在出生后都具有更长时间的可塑性。这种延长的可塑性潜力可能通过出生后的经验以支持人类特有的感知和认知能力的方式促进皮质回路的塑造。
