Figure 4.

Spontaneous slow oscillation in the presence of STDP. A, B, Representative examples of the network activity during early (A) and late (B) stages of simulation. Top, Up-state initiation sites are indicated by black dots. The black triangular indicates the time interval expanded below. Middle, Characteristic example of the network dynamics. Membrane voltage of pyramidal neurons in layer II/III/IV is indicated with a color code; white stars indicate the site of Up-state initiation. Bottom, Probability of Up-state initiation across neurons. The dotted line represents mean ± 2 STDs. The red curve represents the smoothed histogram by Gaussian filter. Synaptic reorganization leads to appearance of the local groups of neurons preferentially initiating Up states (near cells 50 and 150) during the late stage of simulation (*p < 0.01). C, The percentage change of synaptic weights at time t = 1000 s compared with the initial (t = 0) synaptic weights shows increase (red) or decrease (blue) of synaptic weights. The x-axis gives the index of the postsynaptic neuron; the y-axis represents the left (−) and right (+) 10 presynaptic neurons relative to the postsynaptic neurons at x-axis. D, At t = 5000 s, total input synaptic weight received by each neuron (top) and recurrent input strength and spatial gradient of synaptic weights (bottom). Note the group of neurons in the middle (neurons 80–120) with strongly asymmetric connectivity matrix (with connections from one direction of the network enhanced while the connections from the opposite direction reduced) that had high absolute amplitude of spatial gradient would have low probability to initiate the Up states. E, Time evolution of the total (net) input synaptic weight per neuron for 200 pyramidal neurons from layer II/III/IV. F, Individual synaptic weights of two neurons (indicated by stars in D) with low (left) and high (right) net synaptic weight. G, Time evolution of the size (neuron count) of the cell population that had strongly asymmetric connectivity matrix.