Nature - USA (2020-01-16)

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nature research | reporting summary

October 2018

Field-specific reporting

Please select the one below that is the best fit for your research. If you are not sure, read the appropriate sections before making your selection.

Life sciences Behavioural & social sciences Ecological, evolutionary & environmental sciences

For a reference copy of the document with all sections, see nature.com/documents/nr-reporting-summary-flat.pdf

Life sciences study design

All studies must disclose on these points even when the disclosure is negative.

Sample size No statistical methods were used to predetermine sample size. At least n = 3 mice were used for each type of experiment, and experiments

were performed over several days for each animal, as is typical in electrophysiological studies of motor control in vertebrates. Due to the lack

of post-laser reaches in one Sim1-Cre X Ai32 mouse, this animal was not included for the subset of analyses focusing on post-laser reaches

(leaving n = 2 mice for these analyses, but n = 3 mice for the other analyses).

Data exclusions Cortical recordings were aborted when the quality of the raw signals was very poor (n = 2 VGAT-ChR2-EYFP mice and n = 1 Sim1-Cre X Ai32

mouse). For the simultaneous recordings in thalamus and cortex, sessions were excluded when the raw signals were poor in one or both

regions or when either histology or optogenetic tagging attempts indicated that the first probe was not in motor thalamus (n = 15 sessions).

Replication The main results from each experiment were identified in a subset of sessions and replicated in subsequent sessions. In cases where some

differences were observed between mice or sessions (e.g. the limb oscillation under 10 Hz stimulation in Fig. E9), this is stated in the text and

shown in the figures.

Randomization Not applicable: all experimental manipulations were performed at the level of trials within each session, and there was no allocation of

animals into different treatment groups.

Blinding Because the experimental manipulations occurred at the level of trials (laser stimulation vs no stimulation), it was not possible to blind the

experimenter to the trial type. There was no allocation of animals into different treatment groups.

Reporting for specific materials, systems and methods

We require information from authors about some types of materials, experimental systems and methods used in many studies. Here, indicate whether each material,

system or method listed is relevant to your study. If you are not sure if a list item applies to your research, read the appropriate section before selecting a response.

Materials & experimental systems

n/a Involved in the study

Antibodies

Eukaryotic cell lines

Palaeontology

Animals and other organisms

Human research participants

Clinical data

Methods

n/a Involved in the study

ChIP-seq

Flow cytometry

MRI-based neuroimaging

Animals and other organisms

Policy information about studies involving animals; ARRIVE guidelines recommended for reporting animal research

Laboratory animals Mice of either sex were used, at age 8-25 weeks. The following mouse lines were used:

(1) VGAT-ChR2-EYFP (Slc32a1-COP4*H134R/EYFP)

(2) Vglut2-IRES-Cre

(3) Ai32 (Rosa-CAG-LSL-ChR2(H134R)-EYFP-WPRE)

(4) Ai32 (Rosa-CAG-LSL-ChR2(H134R)-EYFP-WPRE) crossed to one of the following driver lines:

(4a) Tlx3-Cre PL56Gsat

(4b) Sim1-Cre KJ18Gsat

(4c) Rbp4-Cre KL100Gsat

Wild animals N/A

Field-collected samples N / A

Ethics oversight All procedures were approved by the Institutional Animal Care and Use Committee at Janelia Research Campus (protocols 13-99,

16-139, and 19-177).