Supplemental Experimental Procedures Stereotaxic Surgery

movement had ceased, the animals were placed into a stereotaxis apparatus (Kopf). Approximately 15 min before virus delivery the mice received an intraperitoneal injection of 1 ml 20 % Manitol to increase virus spread (Burger 2005). A small incision was made to expose the skull and a 28 gauge Hamilton syringe was inserted into the brain at bregma level, 2 mm lateral to the midline. Injection flow was controlled with a micro-injector (Micro 4 ™, World Precission Instruments), by pushing down the plunger at controlled speed. At 4.2 mm dorsal from bregma, a 1 s pulse injection was given at 80 nl/sec, then the needle was pulled up 0.2 mm and injection was continued at 80 nl/min to inject a total of 2 µl. After each 400- 600 µl the needle was pulled up 0.5 mm to cover a ventral to dorsal range of 4 mm to 2.5 mm within the striatum. The needle was left for another minute at the 2.5 mm position, pulled up for 0.5 mm and left at this position for 1 min without injection, before it was removed. The skin incision was closed with Vetbond ™ glue (3M) and locally treated with Marcaine ® (Hospira) for pain relief. The animal received a 150 µl subcutaneous injection of 3 µg/ml ketoprofen for additional pain relief and help with dehydration, and was kept on a heating pad until waking up. Open Field Tests Animals were transferred into the open field apparatus directly from their home cage. The movement of u