Mice were anesthetized with isoflurane and held in place with a head post cemented to the skull. All incisions were infiltrated with lido-caine. A small craniotomy was made over barrel cortex approximately 200 μm anterior to the virus injection site. Extracellular single-unit and LFP recordings were made with tetrodes or stereotrodes. Intracellular recordings were conducted by whole-cell in vivo recording in current clamp mode. Stimulus control and data acquisition was performed using software custom-written in LabView (National Instruments) and Matlab (The Mathworks). Further electrophysiology methods and a description of the reversal potential calculation are given in Supplementary Methods .
Light stimulation was generated by a 473 nm laser (Shanghai Dream Lasers) controlled by a Grass stimulator (Grass Technologies) or computer. Light pulses were given via a 200-μm diameter, unjacketed optical fibre (Ocean Optics) positioned at the cortical surface 75–200 μm from the recording electrodes. For experiments using the broad range of light-stimulation frequencies (8, 16, 24, 32, 40, 48, 80, 100 and 200 Hz), we stimulated in bouts of 3 s of 1-ms pulses at 46 mW mm−2 at each frequency in a random order. In a subset of these experiments, we stimulated at 31, 46 and 68 mW mm−2.
Vibrissae were stimulated by computer-controlled movements of piezoelectric wafers (Piezo Systems). Vibrissa stimulations were single high-velocity deflections in the dorsal and then in the ventral direction (~6 ms duration). In most cases, adjacent vibrissae that yielded indistinguishable amplitude responses during hand mapping were deflected simultaneously. Vibrissa stimulations evoked layer 4 RS spike responses with an onset latency of 9.1 ± 0.08 ms. For RS cell response suppression experiments, light pulses were given on randomly interleaved trials. For gamma-phase experiments, we gave a series of trials each consisting of a 1-s series of 1-ms light pulses at 40 Hz, with a single whisker deflection after the thirtieth light pulse. The precise timing of the whisker deflection relative to the light pulses was varied across five phase points. Each of the five phase points was included in a random order across a minimum of 250 total trials.
Unit and LFP analysis used software custom-written in Igor Pro (Wavemetrics). For each stimulation frequency, we measured the relative power in an 8-Hz band centred on that frequency. For each recording site, we measured power from 5–10 LFP traces under each condition. Example power spectra are averages of the power spectra from 5–10 traces of unfiltered LFPs from individual experiments. Relative power was calculated by measuring the ratio of power within the band of interest to total power in the power spectrum of the unfiltered LFP. We also measured the power ratio: Plight/Pbaseline, where Plight is the relative power in a frequency band in the presence of light stimulation and Pbaseline is the power in that band in the absence of light stimulation. All numbers are given as mean ± s.e.m., except where otherwise noted.
Light stimulation was generated by a 473 nm laser (Shanghai Dream Lasers) controlled by a Grass stimulator (Grass Technologies) or computer. Light pulses were given via a 200-μm diameter, unjacketed optical fibre (Ocean Optics) positioned at the cortical surface 75–200 μm from the recording electrodes. For experiments using the broad range of light-stimulation frequencies (8, 16, 24, 32, 40, 48, 80, 100 and 200 Hz), we stimulated in bouts of 3 s of 1-ms pulses at 46 mW mm−2 at each frequency in a random order. In a subset of these experiments, we stimulated at 31, 46 and 68 mW mm−2.
Vibrissae were stimulated by computer-controlled movements of piezoelectric wafers (Piezo Systems). Vibrissa stimulations were single high-velocity deflections in the dorsal and then in the ventral direction (~6 ms duration). In most cases, adjacent vibrissae that yielded indistinguishable amplitude responses during hand mapping were deflected simultaneously. Vibrissa stimulations evoked layer 4 RS spike responses with an onset latency of 9.1 ± 0.08 ms. For RS cell response suppression experiments, light pulses were given on randomly interleaved trials. For gamma-phase experiments, we gave a series of trials each consisting of a 1-s series of 1-ms light pulses at 40 Hz, with a single whisker deflection after the thirtieth light pulse. The precise timing of the whisker deflection relative to the light pulses was varied across five phase points. Each of the five phase points was included in a random order across a minimum of 250 total trials.
Unit and LFP analysis used software custom-written in Igor Pro (Wavemetrics). For each stimulation frequency, we measured the relative power in an 8-Hz band centred on that frequency. For each recording site, we measured power from 5–10 LFP traces under each condition. Example power spectra are averages of the power spectra from 5–10 traces of unfiltered LFPs from individual experiments. Relative power was calculated by measuring the ratio of power within the band of interest to total power in the power spectrum of the unfiltered LFP. We also measured the power ratio: Plight/Pbaseline, where Plight is the relative power in a frequency band in the presence of light stimulation and Pbaseline is the power in that band in the absence of light stimulation. All numbers are given as mean ± s.e.m., except where otherwise noted.
