Limited options exist to evaluate the development of hippocampal function in young children. Research has established that trace eyeblink conditioning (EBC) relies on a functional hippocampus. Hence, we set out to investigate whether trace EBC is linked to hippocampal structure, potentially serving as a valuable indicator of hippocampal development. Our study explored potential associations between individual differences in hippocampal volume and neurite density with trace EBC performance in young children. We used onset latency of conditioned responses (CR) and percentage of conditioned responses (% CR) as measures of hippocampal-dependent associative learning. Using a sample of typically developing children aged 4 to 6 years (N = 30; 14 girls; M = 5.70 years), participants underwent T1- and diffusion-weighted MRI scans and completed a 15-min trace eyeblink conditioning task conducted outside the MRI. % CR and CR onset latency were calculated based on all trials involving tone-puff presentations and tone-alone trials. Findings revealed a connection between greater left hippocampal neurite density and delayed CR onset latency. Children with higher neurite density in the left hippocampus tended to blink closer to the onset of the unconditioned stimulus, indicating that structural variations in the hippocampus were associated with more precise timing of conditioned responses. No other relationships were observed between hippocampal volume, cerebellum volume or neurite density, hippocampal white matter connectivity and any EBC measures. Preliminary results suggest that trace EBC may serve as a straightforward yet innovative approach for studying hippocampal development in young children and populations with atypical development.

中文翻译：

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海马体的神经突密度与 4 至 6 岁儿童的微量眨眼条件反射潜伏期相关

评估幼儿海马功能发育的选择有限。研究表明，微量眨眼调节（EBC）依赖于功能性海马体。因此，我们着手研究微量 EBC 是否与海马结构有关，是否有可能作为海马发育的一个有价值的指标。我们的研究探讨了幼儿海马体积和神经突密度的个体差异与微量 EBC 表现之间的潜在关联。我们使用条件反应的起始潜伏期 （CR）和条件反应的百分比（% CR）作为海马依赖性联想学习的衡量标准。使用 4 至 6 岁正常发育儿童样本（N  = 30；14 名女孩；M  = 5.70 岁），参与者接受 T1 和扩散加权 MRI 扫描，并完成 MRI 之外进行的 15 分钟微量眨眼调节任务。% CR和CR 起始潜伏期是根据涉及音调呈现和仅音调试验的所有试验计算的。研究结果揭示了左侧海马神经突密度较高与CR 发作潜伏期延迟之间存在联系。左侧海马体神经突密度较高的儿童往往在接近非条件刺激开始时眨眼，这表明海马体的结构变化与更精确的条件反应时间相关。在海马体积、小脑体积或神经突密度、海马白质连接性和任何 EBC 测量之间没有观察到其他关系。初步结果表明，微量 EBC 可能是研究幼儿和非典型发育人群海马发育的一种简单而创新的方法。