library_construction_protocol: cortical brain tissue was removed and flash frozen using liquid nitrogen. Cortices were then homogenized using a Dounce homogenizer in lysis buffer (10mM Tris-HCl, ph 7.5, 10mM NaCl, 3mM MgCl2, and 0.1% Nonidet P40 in nucleuase-free water). Homogenized tissue was incubated for 15 minutes and subsequently filtered through a 30 μm cell strainer. The filtered cell suspension was centrifuged (to pellet the nuclei. Nuclei were washed and filtered twice through a 40 μm cell strainer using 2% BSA in sterile PBS with 0.2 U/μl RNase inhibitor (nuclei wash). After resuspension in 500 μl nuclei wash and 900 μl 1.8M sucrose, nuclei were carefully layered on top of 500 μl of 1.8M sucrose and centrifuged (13000g, 45 min, 4°C) to remove myelin debris. The pellet was resuspended in nuclei wash and filtered again through a 40 μm Cell Strainer.