Article Figures & Data
Figures
- Fig. 1.
The activity-dependent dynamics of vesicle depletion add negative autocorrelations to sequences of synaptic transmissions. A, Autocorrelation of a Poisson spike train of average rate 15 Hz. B, Autocorrelation of the transmissions of this spike train through a model synapse with a constant probability of transmission. C, Autocorrelation of the transmissions of the Poisson train through a model synapse withp = 0.2 and τD = 500 msec. In both B and C,Nmax = 3, and 23% of presynaptic spikes were transmitted.
- Fig. 2.
Decorrelation of a saccade model spike train by a stochastic synapse with vesicle depletion. A, Autocorrelation of the presynaptic saccade model train of average rate 15 Hz (black line) and of the transmissions through a model synapse with p = 0.5 and τD = 350 msec (black bars). Thirty-three percent of presynaptic spikes were transmitted.B, Autocorrelation of the transmissions through a model synapse with p = 0.5 and τD = 70 msec (black line) or 1750 msec (gray line). Sixty-five and 10% of presynaptic spikes were transmitted, respectively. C, Autocorrelation of the transmissions through a model synapse with p = 0.5 and τD = 350 msec when the average presynaptic rate is 3 Hz (black line) or 75 Hz (gray line). Sixty-nine and 10% of presynaptic spikes were transmitted, respectively. D, Autocorrelation of the transmissions through a model synapse with τD = 350 msec and p = 0.1 (black line) or 1.0 (gray line). Seventeen and 38% of presynaptic spikes were transmitted, respectively. In A,B, and D, the average presynaptic rate is 15 Hz. In A–D, Nmax = 3.
- Fig. 3.
Removal of positive autocorrelations from a model burst train by a stochastic synapse with activity-dependent transmission failures. A, The presynaptic burst train has strong positive autocorrelations followed by near-maximal negative autocorrelations. B, Autocorrelation of the transmissions through a model synapse with τD = 15 msec, p = 0.5, andNmax = 1 (left) or 3 (right). Twenty-six and 67% of presynaptic spikes were transmitted, respectively.
- Fig. 4.
Spike trains recorded from area V1 of a monkey freely viewing natural scenes. Traces 1–14 show the responses of 14 different neurons, and traces V andH indicate the horizontal and vertical eye positions.
- Fig. 5.
Decorrelation of three typical spike trains recorded from freely viewing monkeys. Black lines, Spike trains from three recorded neurons showing strong positive autocorrelations of differing magnitudes and time scales. Average firing rates were left, 15.2 Hz; middle, 12.5 Hz; and right, 3.2 Hz. Black bars, Corresponding autocorrelation of the transmissions through a model synapse with Nmax=1, p =1, and τD = 150 msec. Percentages of presynaptic spikes transmitted were left, 19%; middle, 27%; and right, 52%. The left,middle, and right panels correspond to neurons 14, 1, and 13, respectively, in Figure 4.
- Fig. 6.
Matching of input and output firing rates and autocorrelations. A, Comparison of the postsynaptic firing rate (solid line) of an integrate-and-fire neuron receiving 30 inputs (as described in Results and inC) with the firing rate of one of its feedforward inputs (dashed line). The slight discrepancy between the input and postsynaptic firing rates for the initial lower-rate segment arises because the integrate-and-fire neuron fires more rapidly at low rates than the linear model used in the calculation of the matching conditions. B, Autocorrelation of one of 333 presynaptic spike trains generated from the saccade model (black line) and of the corresponding transmissions through one of the model synapses (Nmax = 3;p = 0.25; and τD = 350 msec;black bars). The other 667 presynaptic inputs were generated by a 15 Hz constant-rate Poisson process. C, Schematic of the pattern of arrivals of an identical change in rate for the 333 saccade model afferents to the integrate-and-fire model neuron. For the simulations, we have defined a fixed order in which neurons switch rates for each simulated saccade. D, Autocorrelation of the spike train generated by the postsynaptic neuron (average rate, 15 Hz). The smaller autocorrelations in the first two time bins reflect the postspike dynamics of the integrate-and-fire neuron, an effect not included in the input trains.
