File:DA Models Fig2.jpg

Summary

Stimulus-selective persistent activity, presumably underlying working memory, and D1 modulation in a PFC network model. A) Structure of a network model underlying the simulations shown in B & C. Pyramidal cells (PC) are recurrently coupled by excitatory synapses, and also excite a population of interneurons (IN) which feeds back inhibition into all pyramidal cells. Stimulus-specific persistent (delay) activity could be produced by cell assemblies (highlighted by the yellow square) through strong synaptic connections. Once a threshold of activation is exceeded, these strong recurrent excitatory inputs could maintain stimulus-specific enhanced firing rates as observed experimentally. Slightly modified from Durstewitz and Seamans (2002) and reprinted from Durstewitz and Seamans (2008) with permission from Elsevier (Copyright 2002, 2008). B) An external stimulus switches a cell assembly from a low spontaneous (1) into a stimulus-specific high persistent (2) activity state that is maintained even after withdrawal of the initiating stimulus, thus keeping an online memory of the stimulus. D1 stimulation differentially suppresses low (spontaneous) and enhances high (memory) activity in these simulations. Reprinted from Durstewitz and Seamans (2002) with permission from Elsevier (Copyright 2002). C) Numerically derived state space representation of the model dynamics, spanned by the average firing rate of the PCs (x-axis) and the INs (y-axis) within a cell assembly. Arrows indicate the flow (with length of all arrows normalized to 1), and the red and blue curves are the nullclines of the system. Firing rates converge to one of two fixed points (labeled ‘1’ and ‘2’), corresponding to the low spontaneous and high persistent firing rate attractors illustrated in B. The dashed green line shows the separatrix between the two regions of convergence, and can be seen as a threshold which a stimulus has to overcome to switch the dynamics from the low to the high firing rate attractor state. Within this representation, D1-stimulation leads to a stretching of the PC nullcline (light blue curve). Reprinted from Durstewitz and Seamans (2002) with permission from Elsevier (Copyright 2002).

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