Fig 2. The delay-associated state of the mesocortical dynamics is characterized by the global equilibrium state of its various dynamical elements.
(A) Given a fixed value of D1R-sensitivity D1Rsens (here D1Rsens = 3, normal control), the bifurcation profiles of the dynamical elements are shown with DA releasability RDA as the bifurcation parameter. Critical RDA, and the corresponding critical cortical dopamine content [DA] and D1R stimulation level D1Ract, mark the beginning of bistable regime favoring the working memory maintenance during delay period. The higher stable states of the bifurcation profiles are together associated with the sustained-firing state of the cortical dynamics whereas the lower stable states together signify the basal spontaneous-activity state. The ranges of [DA] and D1Ract spanned by their higher stable states represent the spans or windows of cortical DA content and D1R stimulation, respectively, underlying the entire modulation profile of the cortical dynamics. The maximum limit to which [DA] or D1Ract may may increase with increase in RDA marks the saturation level. The cue-threshold in the aPN bifurcation profile signifies the minimum excitation of the pyramidal population by cue input, which causes switching to the sustained-firing state. (B) Alteration in D1Rsens further affects the bifurcation profiles. Most prominently, increase in D1Rsens causes leftward shift of the bifurcation region.