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. 2013 Jul 10;33(28):11515–11529. doi: 10.1523/JNEUROSCI.5044-12.2013

Figure 4.

Figure 4.

The cortical microcircuit model forms a memory trace in the form of a sequentially activated assembly of neurons for a reoccurring subpattern within its high-dimensional input stream. A, Top: The stimulus consisted of 100 Poisson spike trains of a constant rate (5 Hz) into which a frozen Poisson spike pattern at 3 Hz was embedded in random intervals (top left, red spikes). New 2 Hz Poisson spike trains (black spikes) were superimposed over each pattern presentation. The original pattern had 300 ms duration. During testing, pattern presentations were time warped with a random factor between 0.5 and 2 (top right). Bottom: Response of the network to test stimuli shown above before (left) and after (right) 100 s of applying STDP within the network for such input stream (that contained ∼150 pattern presentations). Shown is the activity of 20 randomly selected neurons. To illustrate the sequential activation during pattern presentations, neurons that now respond primarily to this pattern are sorted according to their mean activation time during the pattern (B). B, Average activation of the neurons in the emergent assembly during 100 pattern presentations. Neurons are sorted by their mean activation time (white dots) defined as the center of mass of their temporal activity profiles. C, Histogram of rank correlations between mean activation times for individual pattern presentations and for the average response in B. Most correlations are greater than zero, indicating that the sequence of activations is mostly preserved across pattern presentations. D, The response to the pattern is unaffected if during training it is sometimes preceded by one of two other Poisson spike patterns of the same length. Shown is the average activation of the neurons (as in B) for an experiment in which 10% of the presentations were preceded by pattern 1 and another 10% by pattern 2. It is interesting to compare this result with Figure 9, where the emergence of different assemblies for the same input pattern is demonstrated if it regularly occurs in two different temporal contexts.