Figure 5.
Adaptation reduces tonic and burst firing rates, and synchronous spike counts, in VPm sensory responses. A, top, Experimental setup. We recorded extracellular spiking in VPm of the awake mouse, primarily using high-density silicon probes (see Materials and Methods). Bottom, Criteria for classification of putative tonic (black) and burst (red) VPm spikes. B, Grand PSTHs for putative tonic (black) and burst (red) VPm spikes from a subset of all recording sessions. C, Grand-average mean (±SEM) rates for spontaneous activity (i.e., no sensory stimulation) and early (0–200 ms) and late (500–700 ms) windows following onset of sensory white noise (***p < 0.0005, Wilcoxon signed-rank test). Tonic: spontaneous rate = 10.28 ± 1.31 Hz; white noise early rate = 16.69 ± 2.77 Hz; white noise late rate = 14.84 ± 2.39 Hz, mean ± SEM. Spontaneous versus white noise early: W = 42, p = 8.91 × 10−5; spontaneous versus white noise late: W = 75, p = 1.12 × 10−3; white noise early versus white noise late: W = 135, p = 0.045, Wilcoxon signed-rank test; burst: spontaneous rate = 0.36 ± 0.07 Hz, white noise early rate = 0.85 ± 0.2 Hz; white noise late rate = 0.26 ± 0.08 Hz, mean ± SEM. Spontaneous versus white noise early: W = 65.5, p = 3.0 × 10−3; spontaneous versus white noise late: W = 51, p = 4.65 × 10−3; white noise early versus white noise late: W = 37, p = 4.35 × 10−4, Wilcoxon signed-rank test, N = 30 units from 9 sessions. D, Grand PSTHs for tonic (black) and burst (red) spikes from all putative VPm neurons, for 300°/s punctate stimulus. Note the presence of both a short-latency primary peak, and a shorter, secondary peak in tonic firing rates (E). This secondary peak in the grand PSTH resulted from a subset of neurons with both early and late responses, often within individual trials, and was likely evoked by the return of the whisker to resting position in the second half of the sawtooth waveform. E, Across-neuron mean (±SEM) firing rates for all putative VPm neurons (**0.001 ≤ p < 0.01; ***p < 0.001, Wilcoxon singed-rank test). Tonic 300°/s mean ± SEM rate control: 30.2 ± 3.41 Hz, adapted: 24.32 ± 2.92 Hz, 19.5% decrease, W = 83, p = 0.002, Wilcoxon signed-rank test, N = 30 units; 900 control: 29.98 ± 3.47 Hz, adapted: 26.87 ± 3.18 Hz, W = 44.5, p = 0.22, N = 16 units; burst: 300°/s control: 3.79 ± 1.08, adapted: 1.37 ± 0.73 Hz, 64.0% decrease, W = 47, p = 6.21 × 10−4; 900°/s control: 5.75 ± 3.13 Hz, adapted: 2.02 ± 0.88, 64.9% decrease, W = 5, p = 4.6 × 10−3. F, Grand shuffle-corrected cross-correlograms for all simultaneously-recorded putative VPm neurons, for the control (black) and adapted (gray) conditions. Bands indicate 97.5% confidence intervals (from re-sampling spikes with replacement; see Materials and Methods). G, Synchronous AP counts for control, adapted, and hybrid conditions (see Materials and Methods), calculated from grand CCGs. (Error bars indicate 97.5% confidence intervals; *p < 0.025, re-sampling spikes with replacement; see Materials and Methods.) 300°/s mean ± 97.5% confidence interval control: synch AP count = 46.69 ± 8.12 spikes/pair; adapted: 17.29 ± 4.0 spikes/pair; hybrid: 20.4 ± 4.25 spikes/pair; N = 48 valid pairs from 7 sessions; 900°/s control: 51.38 ± 8.22 spikes/pair; adapted: 30.81 ± 6.3 spikes/pair; hybrid: 31.3 ± 5.35 spikes/pair; N = 37 pairs from 3 sessions (see Materials and Methods for definition of “valid pairs”).