Human tissue was obtained under a protocol approved by the Research Compliance Office at Stanford University. The tissue was processed using an adapted protocol47. Briefly, GW18 or GW20 frontal brain tissue was embedded in 4% low-melting point agarose in bubbled artificial cerebrospinal fluid (ACSF: 125 mM NaCl, 2.5 mM KCl, 1 mM MgCl2, 2 mM CaCl2, 1.25 mM NaH2PO4, 25 mM NaHCO3, 25 mM D-(+)-Glucose) and either sectioned using a Leica VT1200 Vibratome at 300–500 μm in ice-cold, bubbled ACSF, or cut using the sharp end of a gauge–22 needle to obtain 1–2 mm thick sections. The sections were then placed in tissue culture plates containing culture media (66% BME, 25% Hanks, 5% FBS, 1% N-2, 1% penicillin, streptomycin and glutamine; all from Invitrogen) and 0.66% D-(+)-Glucose (Sigma) and incubated (37°C, 5% CO2) with the Dlxi1/2b::eGFP lentivirus for 30 min to 1 hr. Sections were then transferred to cell culture membrane inserts (diameter, 13 mm; pore size, 8 μm; Costar) and incubated in culture media at 37°C, 8% O2, 5% CO2 for up to 8 days. Half media changes were
