Data in Figure S2C were re-analyzed from a previous publication16 (link) to calculate the time-course of optogenetic responses using z-scored firing rates. To record single unit electrophysiological activity from medium spiny neurons and fast-spiking interneurons in vivo during optogenetic silencing of FSIs in awake, freely moving mice, we implanted multi-electrode arrays into striatum of PV-2A-cre mice. Under anesthesia in a stereotactic surgery, the scalp was opened and a hole was drilled in the skull (+0.5 to +1.5 mm AP, −2.5 to −1.5 mm ML from bregma). We injected 1000 nL of AAV (AAV5-EF1α-DIO-eNpHR3.0-YFP) the coordinates +1.0 AP, +/−2.2 ML, −2.5 DV from bregma in PV-2A-cre mice (Jackson Stock #012358). Two skull screws were implanted in the opposing hemisphere to secure the implant to the skull. Dental adhesive (C&B Metabond, Parkell) was used to fix the skull screws in place and coat the surface of the skull. An array of 32 microwires (4×8 array, 35 μm tungsten wires, 150 μm spacing between wires, 150 – 200 μm spacing between rows; Innovative Physiology) was combined with a 200 μm diameter optical fiber (Thorlabs FT200UMT, flat cut) and lowered into the striatum (2.5 mm below the surface of the brain) and cemented in place with dental acrylic (Ortho-Jet, Lang Dental). After the cement dried, the scalp was sutured shut. Animals were allowed to recover for at least seven days before striatal recordings were made.
Voltage signals from each site on a 32-channel microwire array were recorded in awake, freely moving mice in an open field arena. Signals were band-pass-filtered, such that activity between 300 and 6,000 Hz was analyzed as spiking activity. This data was amplified, processed and digitally captured using commercial hardware and software (Plexon or SpikeGadgets). Single units were discriminated with principal component analysis (Plexon Offline Sorter, or SpikeGadgets MatClust). Two criteria were used to ensure quality of recorded units: (1) recorded units smaller than 100 μV (~3 times the noise band) were excluded from further analysis and (2) recorded units in which more than 1% of interspike intervals were shorter than 2 ms were excluded from further analysis. FSIs and MSNs were distinguished based on waveform and firing rate as previously described16 (link). Green light pulses 1 sec in duration and 3 mW in brightness were delivered through a 200 μm optical fiber contained within the implanted microwire recording array with a duty cycle of 25% for 60 min (900 pulses for 1 s; 30 pulses for 30 s).
Voltage signals from each site on a 32-channel microwire array were recorded in awake, freely moving mice in an open field arena. Signals were band-pass-filtered, such that activity between 300 and 6,000 Hz was analyzed as spiking activity. This data was amplified, processed and digitally captured using commercial hardware and software (Plexon or SpikeGadgets). Single units were discriminated with principal component analysis (Plexon Offline Sorter, or SpikeGadgets MatClust). Two criteria were used to ensure quality of recorded units: (1) recorded units smaller than 100 μV (~3 times the noise band) were excluded from further analysis and (2) recorded units in which more than 1% of interspike intervals were shorter than 2 ms were excluded from further analysis. FSIs and MSNs were distinguished based on waveform and firing rate as previously described16 (link). Green light pulses 1 sec in duration and 3 mW in brightness were delivered through a 200 μm optical fiber contained within the implanted microwire recording array with a duty cycle of 25% for 60 min (900 pulses for 1 s; 30 pulses for 30 s).
