Shaul Druckmann^{1, 5}, Linqing Feng^{2, 5}, Bokyoung Lee^{2, 3}, Chaehyun Yook^{2, 4}, Ting Zhao¹, Jeffrey C. Magee¹, Jinhyun Kim²

¹ Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, Virginia 20147, USA
² Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), 39-1 Hawolgokdong, Seoul, 136-791, Korea
³ Neuroscience program, University of Science and Technology, 176 Gajeongdong, Daejeon, 305-350, Korea
⁴ Department of Biological Science, KAIST, 373-1 Guseongdong, Daejeon, 305-701, Korea
⁵ These authors contributed equally to this work

Corresponding author : Jeffrey C. Magee, Jinhyun Kim

Summary
The organization of synaptic connectivity within a neuronal circuit is a prime determinant of circuit function. We performed a comprehensive fine-scale circuit mapping of hippocampal regions (CA3-CA1) using the newly developed synapse labeling method, mGRASP. This mapping revealed spatially nonuniform and clustered synaptic connectivity patterns. Furthermore, synaptic clustering was enhanced between groups of neurons that shared a similar developmental/migration time window, suggesting a mechanism for establishing the spatial structure of synaptic connectivity. Such connectivity patterns are thought to effectively engage active dendritic processing and storage mechanisms, thereby potentially enhancing neuronal feature selectivity.