Figure 1.
Simulated LGN Responses to Natural Scene Movies at Different Resting Potentials
(A) Four frames of a natural scene movie are shown. Movies were recorded by a camera mounted on the head of a freely roaming cat [23]. The RF center of the simulated neuron is indicated by the yellow circle. The scale bar indicates 1°. The intensity of a 500-ms segment of the movie averaged over all pixels in the RF center is also shown. The thin gray line indicates the mean intensity. The tick marks on the intensity plot indicate the onset times of the corresponding frames. Three stimulus events are colored to correspond to burst events in the responses in (B).
(B) Raster plots of simulated LGN responses to 24 repeats of the 500-ms segment of a natural scene movie shown in (A). Burst events in the responses are highlighted. The colored arrows next to each burst event correspond to the luminance sequences in (A). Responses were simulated using an IFB model. The resting potential of the model ( VR ) and BP of the simulated response to a two-minute segment of natural scene movie that includes the 500-ms segment shown are indicated. The de-inactivation potential and threshold of the burst mechanism ( VT ) was −60 mV. For values of other model parameters, see Materials and Methods.
Figure 2.
The Luminance Sequences That Trigger Burst Events
(A) The BTAs calculated from simulated responses to a two-minute segment of natural scene movie at different resting potentials. The resting potential of the model and BP of the response corresponding to each BTA are indicated. Full spatiotemporal BTAs were calculated, and the plots show the intensity of the BTA averaged over all pixels in the RF center. Each BTA was scaled so that the integral of its absolute value was 1.
(B) A plot of E/I ratio of the BTA versus resting potential for simulated responses to natural scene movies. E/I ratio was calculated as the ratio of the areas of the excitatory and inhibitory components of the BTA (see inset).
(C) The BTAs calculated from the experimental responses of three LGN Y cells recorded at different times during a single experiment to natural scene movies (average of nine different two-minute segments). The BP of each response is indicated. Spatiotemporal BTAs were averaged and scaled as in (A).
(D) A scatter plot of E/I ratio of the BTA versus BP for a sample of 27 LGN cells (11 X cells, 16 Y cells). E/I ratio was calculated as described in (B).
(E) The normalized BTAs for three LGN Y cells. BTAs were normalized for the temporal correlations in the natural scene movies by spectral normalization (see Materials and Methods). The non-normalized BTAs corresponding to each normalized BTAs are shown in gray (same BTAs as in (C)).
(F) A scatter plot of E/I ratio of the normalized BTA versus BP for a sample of 27 LGN cells. E/I ratio was calculated as described in (B).
Figure 3.
Detection of the Onset of Excitatory Luminance Sequences
(A) LGN responses to a noisy stimulus in which an excitatory sequence randomly appeared were simulated with and without bursts using the IFB and IF models (see Materials and Methods). The stimulus was classified as S0 (black) or S1 (red), depending on whether or not each interval contained the excitatory transient of the sequence. A typical realization of the stimulus with SNR = 1/2 is shown (intensity averaged over all pixels in RF center). The black line indicates the actual stimulus and the gray line indicates the underlying sequence.
(B) Voltage traces of the IFB and IF responses to the stimulus shown in (A) at two different resting potentials, VR = −67 mV (top) and VR = −50 mV (bottom), with VT = −60 mV. The interval in the response that corresponds to condition S1 is shaded. (The response was shifted for presentation to remove latency between stimulus and response). The spike threshold ( VΘ, green), burst de-inactivation potential and threshold ( VT, red), and resting potential ( VR, blue) are shown.
(C) The probability distributions of the firing rate of the IFB and IF models during the S0 (black) and S1 (red) stimulus conditions at VR = −67 mV (top) and VR = −50 mV (bottom) with stimulus SNR = 1/2. Distributions were calculated using the response to a stimulus segment that contained 100 sequences.
(D) ROC curves for the IFB and IF models at VR = −67 mV (top) and VR = −50 mV (bottom) calculated from the distributions in (C) using likelihood ratios as described in Materials and Methods. The area under the ROC curve is indicated.
Figure 4.
Detection of the Offset of Inhibitory Luminance Sequences
(A) LGN responses to a noisy stimulus in which an inhibitory sequence randomly appeared were simulated. The stimulus was classified as S0 (black) or S1 (red) depending on whether or not each interval contained the excitatory transient of the sequence. A typical realization of the stimulus with SNR = 1/2 and sequence duration = 128 ms is shown (intensity averaged over all pixels in RF center). The black line indicates the actual stimulus and the gray line indicates the underlying sequence.
(B) Voltage traces of the IFB and IF responses to the stimulus shown in (A) at two different resting potentials, VR = −67 mV (top) and VR = −50 mV (bottom), with VT = −60 mV. The interval in the response that corresponds to condition S1 is shaded (response was shifted for presentation to remove latency between stimulus and response). The spike threshold ( VΘ, green), burst de-inactivation potential and threshold ( VT, red), and resting potential ( VR, blue) are shown.
(C) The probability distributions of the firing rate of the IFB and IF models during the S0 (black) and S1 (red) stimulus conditions at VR = −67 mV (top) and VR = −50 mV (bottom).
(D) ROC curves for the IFB and IF models at VR = −67 mV (top) and VR = −50 mV (bottom). The area under the ROC curve is indicated.
Figure 5.
Sequence Detection at Different Resting Potentials
(A) The temporal profile of the excitatory sequence and the area under the ROC curves for the IFB and IF models in the excitatory sequence detection task at different resting potentials with stimulus SNR = 1/2.
(B) The temporal profile of the inhibitory sequence and the ROC areas for the IFB and IF models in the task involving the detection of the offset of inhibitory sequences at different resting potentials with stimulus SNR = 1/2.
(C) The temporal profile of the biphasic sequence and the ROC areas for the IFB and IF models in the biphasic sequence detection task at different resting potentials with stimulus SNR = 1/2.
(D) The ROC areas for the IFB and IF models in the biphasic sequence detection task at different overall firing rates with stimulus SNR = 1/2 and VT = −60 mV. The mean firing rate of the models was varied by changing the gain of the filter relating stimulus intensity to membrane potential.