Figure 4

Simulated Pattern Separation and Completion. Simulated autoassociative functions are illustrated (after deAlmeida et al., 2007). A) The simulated membrane potentials of all 100 excitatory neurons (blue) are illustrated (top) for the time window corresponding to the peak of a single gamma cycle. Green symbols indicate the 10 neurons activated during storage of a stimulus pattern. Also shown (bottom) on an expanded voltage scale are the overlaid near-threshold membrane potentials of the 10 neurons participating in the stimulus pattern (green symbol), the other 90 excitatory neurons in the network, and the inhibitory neuron (red). Pattern separation is successful when, as new memories are stored, only the 10 stimulated neurons fire action potentials, without extraneous firing in the network during the cycle. Pattern separation fails when extraneous firing in one or more neurons outside of the stimulus occurs during pattern storage (black). B) Pattern completion is tested by stimulating only 9 of the 10 neurons in a stored pattern. The neuron that is part of a pattern but not stimulated during the degraded stimulus presentation is depicted with an open green symbol. Pattern completion is successful when synaptic input from the other 9 neurons is able to elicit firing in this neuron (black) within the restricted time window shown, corresponding to a single gamma cycle. Failure of pattern completion occurs when the degraded stimulus is unable to induce firing in the un-stimulated neuron. C) The rate of pattern separation errors is shown as a function of the number of stored patterns for an example set of network parameters. D) The rate of pattern completion errors as a function of the number stored patterns is shown.