Article Figures & Data
Figures
- Figure 1.
Late depolarization is independent of NMDAR activity. A, Vm responses of a cell to a flash stimulus before (left) and after (right) MK801 application (10 mg/kg, i.p.) in individual trials (top) and the mean ± SD of all trials (bottom, n = 49 and 30 trials, respectively). E and L represent early and late response periods, respectively. B, Mean depolarization amplitudes of the late responses in the cell shown in A. There were no significant differences between these two conditions (P = 0.30, t77 = 1.06, Student’s t test).
- Figure 2.
Flash conditioning induces long-term suppression of visually evoked calcium responses in V1 neurons. A, Two-photon image of Fura-2–labeled L2/3 neurons. The bottom trace indicates a raw fluorescence change (|ΔF/F|) in the neuron marked by the yellow arrowhead in response to gratings drifting in eight directions of motion. B, Diagram of the stimulus pairing protocol. Flashes were applied 0.4 s before showing the gratings drifting in a specific direction (paired). This flash-to-drifting grating stimulus pairing was repeated 30 times within a period of 420 s. During stimulus pairing, no flashes were applied preceding gratings that drifted in other directions (nonpaired). C, Stimulus pairing-induced changes in the calcium response of a representative cell. From top to bottom: means ± SEMs (shown as the area) of visually evoked fluorescence traces for all eight directions, mean ± SEM response amplitudes, normalized tuning curves ± SEM, 5–10 min before and 5–10 min after stimulus pairing, and tuning curve change (Δtuning; pp, percentage point). The top traces are ordered according to the labeling of the x-axis of the bottom plot. D, Δtuning was calculated as means ± SEMs of all imaged cells from mice with (+AP5, n = 113 neurons from 4 mice) or without (aCSF, n = 214 neurons from 10 mice) local application of AP5 to the V1. E, Distribution of raw tuning values for the paired stimuli versus the initial tuning value. Each circle indicates a single cell. Cross symbols represent means ± SEMs for data points in quartile sections. The line is the diagonal. F, Same as in E but for the drifting gratings orthogonal to the paired stimuli.
- Figure 3.
Flash stimulus–induced plastic changes in visual responsiveness are correlated with flash stimulus–induced activity alterations during stimulus pairing. A, Δtunings for the paired stimulus of individual cells are plotted against the response modulation during stimulus pairing. Each axis includes a collapsed histogram. The black line represents the linear regression. The top traces represent means ± SEMs (shown as the area) of visually evoked calcium responses to gratings drifting in the paired direction before (black) and during (red) stimulus pairing for two representative cells. B, Coefficients of determination (R 2) between the modulation index and Δtuning for the four directions used in the flash stimulus pairing were determined using simple linear regression. *P = 0.044, r90 = 0.21. C, D, Data from single-unit conditioning experiments are shown in the same manner as in A and B. Numbers in close proximity to the unit traces indicate the average action potential (AP) rates per trial in response to the gratings drifting in the paired direction. **P = 1.8 × 10–3, r21 = 0.64.
- Figure 4.
Flash stimulus–evoked excitatory and inhibitory synaptic inputs underlie sublinear summation of flash and drifting grating stimuli. A, Vm responses of a current-clamped cell to a drifting grating with and without a preceding flash stimulus. From top to bottom: representative traces of individual trials for a drifting grating alone or for a drifting grating with a preceding flash stimulus, mean responses to these two types of stimuli, and differences at a bin size of 100 ms. B, Means ± SEMs of Vm responses to drifting gratings averaged over all directions of 13 recorded neurons. Trials with preceding flashes were plotted against trials with drifting gratings alone. P = 0.115, n = 14, t13 = 1.01. Paired t test. C, Means ± SEMs of Vm responses to drifting gratings preceded by flashes over all directions were plotted against the linear sum of the mean Vm responses to drifting gratings alone and flash-evoked late responses. P = 9.7 × 10–4, t13 = 4.20. D, E, Tuning curves of the mean Vm responses (D) and total number of spikes across all trials (E) for the example cell shown in A. Error bars represent SEMs. F, Flash stimulus–evoked changes in excitatory (orange, ΔGe) and inhibitory (cyan, ΔGi) synaptic conductances of two representative L2/3 neurons. The lower histograms indicate the differences between ΔGe and ΔGi using a bin size of 100 ms. G, ΔGe and ΔGi during the flash stimulus–evoked late responses plotted for every 5-ms bin. The data were obtained from the same neurons shown in F. H, Mean ΔGe and ΔGi of the late responses of all six recorded neurons. Error bars represent SEMs of trial-by-trial variability of conductances during the late response period. Cells that significantly showed ΔGe or ΔGi dominance are plotted in orange or cyan, respectively (P < 0.05, Student’s t test). (I) Top, excitation index calculated from the mean ΔGe and ΔGi during the late responses of the cells shown in H. Bottom, modulation index in Fig. 3A and C were replotted for comparison.
- Figure 5.
Visually evoked responses are bidirectionally modifiable by current injection. A, Diagram of the stimulus pairing protocol. Direct currents were injected for 1.5 s to depolarize (I > 0) or hyperpolarize (I < 0) patch-clamped neurons during 1.5-s gratings drifting in a specific motion direction. The coupling of current injection with the grating stimulus was repeated 30 times. During stimulus pairing, no current was injected for gratings drifting in other directions. B, Representative Vm traces 5 min before (top), during (middle), and 5 min after (bottom) stimulus pairing with depolarizing (cell 3) or hyperpolarizing (cell 4) currents. Ten consecutive sweeps are shown per condition. C, Normalized tuning curves for the grating-evoked spike counts before (black) and after (gray) stimulus pairing (top) and differences (Δtuning, bottom). D, Δtunings of 16 depolarized (left) and 11 hyperpolarized (right) cells are calculated as means ± SEMs. ***P = 2.6 × 10–4, t15 = 4.7; *P = 0.019, t10 = 2.8; paired t test.
- Figure 6.
Late LFP responses are evoked by flashing lights in adult mice. A, Raw (top) and mean-subtracted (bottom) LFP traces recorded from the V1 of an adult mouse. B, Pseudocolored time–frequency map (left) of the mean-subtracted LFP trace and the power spectra of the late response (right). C, Time change in the LFP power and P value from baseline activity at various frequencies.
- Figure 7.
Flash conditioning induces prolonged attenuation of visual perception in adult mice. A, An adult (P68–P75) mouse was placed in the arena surrounded by four screens that intermittently displayed gratings drifting leftward or rightward, and the probability that the mouse moved its head in the same direction as the drifting gratings (tracking rate) was measured. B, Tracking rates were measured 24 h before and 3 and 24 h after local application of tetrodotoxin to the V1. ***P = 1.2 × 10–4 vs. before, t8 = 6.9; paired t test. C, Tracking rates were compared 1 d before and 20 min after flash pairing with horizontally or vertically drifting gratings. **P = 7.1 × 10–3, t11 = 3.3; paired t test. D, Changes in the tracking rates 20 min, 3 h, and 24 h after pairing with horizontally drifting gratings. AP5 was locally injected into the V1 15 min before stimulus pairing (+AP5). 20 min: **P =7.1 × 10–3, t11 = 3.3; 3 h: **P = 7.7 × 10–3, t10 = 3.3; paired t test; §P = 0.029, t22 = 2.3, Student’s t test.
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