School of Psychology, Shandong Normal University, Jinan 250014, China.
F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland 21205.
J Neurosci. 2023 Apr 19;43(16):2874-2884. doi: 10.1523/JNEUROSCI.1488-22.2023. Epub 2023 Mar 22.
The hierarchically organized structures of the medial temporal lobe are critically important for episodic memory function. Accumulating evidence suggests dissociable information processing pathways are maintained throughout these structures including in the medial and lateral entorhinal cortex. Cortical layers provide an additional dimension of dissociation as the primary input to the hippocampus derives from layer 2 neurons in the entorhinal cortex, whereas the deeper layers primarily receive output from the hippocampus. Here, novel high-resolution T2-prepared functional MRI methods were successfully used to mitigate susceptibility artifacts typically affecting MRI signals in this region providing uniform sensitivity across the medial and lateral entorhinal cortex. During the performance of a memory task, healthy human subjects (age 25-33 years, mean age 28.2 ± 3.3 years, 4 female) showed differential functional activation in the superficial and deep layers of the entorhinal cortex associated with task-related encoding and retrieval conditions, respectively. The methods provided here offer an approach to probe layer-specific activation in normal cognition and conditions contributing to memory impairment. This study provides new evidence for differential neuronal activation in the superficial versus deep layers of the entorhinal cortex associated with encoding and retrieval memory processes, respectively, in cognitively normal adults. The study further shows that this dissociation can be observed in both the medial and the lateral entorhinal cortex. The study was achieved by using a novel functional MRI method allowing us to measure robust functional MRI signals in both the medial and lateral entorhinal cortex that was not possible in previous studies. The methodology established here in healthy human subjects lays a solid foundation for subsequent studies investigating layer-specific and region-specific changes in the entorhinal cortex associated with memory impairment in various conditions such as Alzheimer's disease.
内侧颞叶的层次结构对于情景记忆功能至关重要。越来越多的证据表明，包括在内侧和外侧内嗅皮层在内的这些结构中维持着可分离的信息处理途径。皮质层提供了另一个分离维度，因为海马体的主要输入来自内嗅皮层的 2 层神经元，而较深的层主要接收来自海马体的输出。在这里，新的高分辨率 T2 准备功能磁共振成像方法成功地用于减轻通常影响该区域 MRI 信号的磁化率伪影，从而在内侧和外侧内嗅皮层提供均匀的灵敏度。在执行记忆任务期间，健康的人类受试者（年龄 25-33 岁，平均年龄 28.2 ± 3.3 岁，4 名女性）在与任务相关的编码和检索条件相关的内嗅皮层的浅层和深层显示出不同的功能激活。这里提供的方法提供了一种在正常认知和导致记忆障碍的条件下探测层特异性激活的方法。该研究为与编码和检索记忆过程相关的内嗅皮层浅层与深层的神经元激活提供了新的证据，分别在认知正常的成年人中。该研究进一步表明，这种分离可以在内侧和外侧内嗅皮层中观察到。该研究通过使用新的功能磁共振成像方法来实现，该方法允许我们在以前的研究中不可能的情况下在内侧和外侧内嗅皮层中测量稳健的功能磁共振成像信号。在健康人类受试者中建立的方法学为随后的研究奠定了坚实的基础，这些研究旨在调查与各种情况下的记忆障碍相关的内嗅皮层的层特异性和区域特异性变化，例如阿尔茨海默病。
