Supplementary Figure 1: Striatal recordings and cerebellar stimulation.

(a) Single-unit recordings were made in the dorsolateral striatum by using a drivable 8 wire microarray. The left photograph is a Nissl stained section of the striatum and shows the initial implant site in the dorsal edge of the dorsolateral striatum (DLS). Wires were advanced through the DLS after the initial implant in ≈75 μm increments as needed. The right photograph shows the final location of microwires at the end of the series of experiments done in this mouse. To identify the final location of the recording sites at the end of the experiment, current was passed through each electrode to produce lesions, and the animal was killed and the brain fixed soon after. Red arrows indicate the position of two such lesions. (b) To electrically stimulate the dentate nucleus, a bipolar stimulating electrode was stereotaxically implanted into the contralateral cerebellum during the same surgery when the recording microarray was implanted in the striatum. The stimulating electrode tract is indicated by the red arrows. (c) To stimulate the dentate nucleus optogenetically, ChR2 was expressed in the dentate nucleus by stereotaxic injection of an AAV. A fiber optic implant was stereotaxically placed immediately above the injection site, contralateral to the recording site. The specificity of expression of ChR2 was examined by examination of ChR2-YFP expression (indicated in green; DAPI staining in blue). The location of the fiber optic was also ascertained at the end of each experiment histologically. In the case shown, the fiber optic tract is indicated by red arrows. (d) In separate experiments to confirm that optogenetic stimulation reliably increased firing rate of neurons in the DN, single-unit recordings were made from ChR2-expressing neurons in the DN in awake, head-restrained mice using an optrode. The optrode, made by fixing a fiber optic to a recording electrode, allowed for simultaneous optogenetic stimulation and recording of DN neurons. An example neuron is shown. Stimulus was delivered at time zero.Abbreviations: 4V: 4th ventricle; Int: interpositus nucleus; DN: dentate nucleus; LV: lateral ventricle; DLS: dorsolateral striatum; CC: corpus callosum