Mice

This study is based on data from 71 mice (age > P60, we used both male and female) (Supplementary Table 1, 2). We used six transgenic mouse lines: PV-IRES-Cre⁴⁵, Ai32 (Rosa-CAG-LSL-ChR2(H134R)-EYFP-WPRE, JAX 012569)⁴⁶, VGAT-ChR2-EYFP³², Gad2-IRES-Cre (a gift from Boris Zemelman), Ai35D (Rosa-CAG-LSL-Arch-GFP-WPRE, JAX 012735)⁴⁶, and Olig3-cre⁴⁷.

All procedures were in accordance with protocols approved by the Janelia Institutional Animal Care and Use Committee. Detailed information on water restriction, surgical procedures and behavior have been published^3,28. All surgical procedures were carried out aseptically under 1-2 % isofluorane anesthesia. Buprenorphine HCl (0.1 mg/kg, intraperitoneal injection; Bedford Laboratories) was used for postoperative analgesia. Ketoprofen (5 mg/kg, subcutaneous injection; Fort Dodge Animal Health) was used at the time of surgery and postoperatively to reduce inflammation. After the surgery, mice were allowed free access to water for at least three days before start of water restriction. Mice were housed in a 12:12 reverse light:dark cycle and behaviorally tested during the dark phase. A typical behavioral session lasted 1 to 2 hours and mice obtained all of their water in the behavior apparatus (approximately 1 ml per day; 0.3 ml was supplemented if mice drank less than 0.5 ml). On other days mice received 1 ml water per day.

Mice were implanted with a titanium headpost ²⁸. For ALM photoinhibition, mice were implanted with a clear skull cap³. Optical fibers for photostimulation or cannulae for muscimol infusion were implanted during the headpost surgery or after behavioral training. Craniotomies for recording were made after behavioral training. All coordinates are given with respect to bregma (anterior-posterior, AP; medial-lateral, ML; dorso-ventral, DV).