Transient WM activity is modulated by synaptic dynamics in STP rate and spiking networks without LPA signaling (Δ<i>U</i> = 0).

A-F Analysis of the STP rate model (see Models and methods, Table C in S1 Text; network parameters as in Table D in S1 Text except otherwise specified). A WM durations for 30 simulations at 10 values of Ub. As the phase transition is crossed, the range of durations of transient population activity upon cue stimulation increases continuously (a hysteresis effect emerges if the cue is weak, see Fig I in S1 Text). Inset: Distribution of transient WM durations of 100 simulations at Ub = 0.17. B-C Two simulations at Ub = 0.17. The external input current with the cue stimulus is shown in the top panel, population activity in the center and synaptic traces (vesicle availability x, Calcium concentration y, and LPA binding ℓ) are shown in the bottom panel. B and C are both in a metastable regime; after 5 and 15 seconds, respectively, the synchronized population activity that emerges after cue presentation is disrupted and the population activity and the synaptic variables return to their baseline values. D Bifurcation diagram, showing stable (blue) and unstable (black) fixed points, as well as the maximal and minimal amplitude of stable limit cycles (red solid line). E-F Analysis of the system before and after the phase transition for Ub = 0.16 and 0.18, respectively. Projections of three trajectories of a system without noise from initial conditions (x, y) = {(0.3, 0.3), (0.3, 0.4)}, which return to the fixed point, and (for E) the last cycle for a simulation with initial condition (x, y) = (0.5, 0.5), onto the x-y-plane. At the initial state, E is set to be at the lower equilibrium state (dE/dt = 0) for the given x, y. In F, the limit cycle is shown in red. G-I Analysis of a spiking network model (see Table A in S1 Text). Parameters as in Table B in S1 Text except otherwise specified. G Transient WM durations for 15 simulations for 6 values of Ub. As Ub increases, the WM cue is first followed by a silent synaptic trace, then by transient and persistent population spiking. Within a small window of values, U modulates the median duration of the transient, actively spiking WM representation. H-I Two simulations for Ub = 0.26 with different transient durations. Panels as in B and C but the subplot in the center shows a rasterplot of 50 neurons of the selective population instead.