Figure 7.
S1 responses to direct optogenetic stimulation of TC terminals are not adapted by sensory white noise. A, Experimental setup for extracellular recordings. S1 spiking activity was recorded in mice lightly-anesthetized with isoflurane (see Materials and Methods). These transgenic mice expressed Channelrhodopsin in VPm cell bodies, axons, and TC axon terminals. An optic fiber positioned above the cortical surface was used to deliver punctate optogenetic stimulation to TC terminals on light feature stimulation trials (see Materials and Methods). B, Grand PSTHs (using all sensory-responsive single-units and multi-units; see Materials and Methods) for sensory feature (black, left) and light feature (blue, right) trials, for control (empty histogram) and adapted (filled histogram) conditions. Inset, Number of recorded units that were significantly responsive to the sensory feature only (“sens only”), the light feature only, both the sensory and light features (“sens and light”), and not responsive to either (“NR”). C, Across-unit mean (±SEM) punctate-stimulus-evoked firing rates versus stimulus condition for all responsive single-units and multi-units, for sensory feature (black, left) and light feature (blue, right) stimuli (***p < 0.001, Wilcoxon singed-rank test). Sensory feature mean ± SEM control: 18.38 ± 1.27 Hz, adapted: 6.59 ± 0.65 Hz, W = 39, p = 1.39 × 10−12 N = 71 units, Wilcoxon signed-rank test. Light feature mean ± SEM control: 11.7 ± 0.95 Hz, adapted: 11.38 ± 0.99 Hz, W = 987, p = 0.19. D, Distributions of normalized adapted responses for all valid units (see Materials and Methods). Triangles at top denote population median values (***p < 0.001, Wilcoxon signed-rank test). Population median normalized adapted response = −0.29 light feature trials, 0.96 sensory feature trials, W = 199, p = 3.12 × 10−11, Wilcoxon signed-rank test. E, Normalized adapted responses to the light feature versus across-trial mean light-evoked rate in the control condition for all 71 units that responded to both sensory and light features (with r and p values from Pearson correlation test). F, left, Experimental setup for in vivo S1 patch clamp recordings in lightly-anesthetized transgenic mice. Right, Across-trial median membrane potential responses to sensory features (black traces) and light features (blue traces), for one example S1 neuron. G, Properties of subthreshold responses to sensory features (left) and light features (right): subthreshold response amplitude (top), and time from stimulus onset to peak subthreshold response (Tpeak, center) for each of the four recorded cells. Dark lines connecting pairs of data points indicate significant difference across stimulus conditions (p < 0.05, Wilcoxon signed-rank test), and light lines indicate non-significance.