Table 2.

Details of network simulations producing memory activity

(a) Model summary
Populations	Single population, E
Connectivity	All-to-all
Neuron model	Leaky integrate-and-fire (LIF) with refractory period
Synapse model	Excitatory AMPA + voltage-dependent NMDA, inhibitory GABA conductances − step increase then exponential decay
Input	Independent fixed-rate Poisson spike trains from populations of Input cells
Measurements	State transitions times via mean population firing rate

(b) Populations
Name	Elements	Size
E	LIF neurons	N = 8,20,30,40 (static) N = 4,8,12,16 (facilitating)

(c) Connectivity
Name	Source	Target	Pattern
EE	E	E	All-to-all, weight W

(d) Neuron and synapse model
Name	LIF neuron
Type	Leaky integrate-and-fire (LIF) with refractory period, and noisy Poisson exponential conductance input
Subthreshold dynamics	$C_m\frac{dV}{dt}=g_L(V-V_L)+g_{\mathrm{EE}}(t)(V-V_E)+g_{\mathrm{AMPA}}(t)(V-V_E)+g_{\mathrm{GABA}}(t)(V-V_I)$
EE synaptic conductance dynamics	$g_{\mathrm{EE}}(t)=g_{\mathrm{EE}}^{max}{\sum }_{\mathrm{cells},i}{s}_i(t)$
	${\tau }_s\frac{d{s}_i}{dt}=-s_i(t)$ between spikes of cell i at times $t_i^{\ast }$ and $s_i(t_i^{\ast +})=s_i(t_i^{\ast -})+\tilde{\alpha }[1-s_i(t_i^{\ast -})]$
Spiking	If $V(t)>V_{th}$ then (1) emit spike with time-stamp $t^{\ast }$ (2) $V(t)\to V_{\mathrm{reset}}$

(f) Input
Type	Description
Poisson generators X = AMPA,GABA	${\tau }_X\frac{d{s}_X}{dt}=-s_X(t)+\sum \delta (t-t_X^{\ast })$
	$P(t\le t_X^{\ast }<t+dt)={\upsilon }_{X}dt$; ${\upsilon }_{\mathrm{AMPA}}={\upsilon }_{\mathrm{GABA}}=800\text{ Hz}$

(g) Measurements
Transition times	Time for $\langle s_{i,\mathrm{EE}}\rangle$ to transition from below 0.05 to above 0.45 ($T_{\mathrm{down}}$) and from above 0.45 to below 0.05 ($T_{\mathrm{up}}$)

(h) LIF neuron parameters
$V_L$	$V_E$	$V_I$	$V_{th}$	$V_{\mathrm{reset}}$	$g_L$	$g_{\mathrm{EE}}^{max}$	$C_m$	$g_{\mathrm{AMPA}}^{max}$	$g_{\mathrm{GABA}}^{max}$	${\tau }_{\mathrm{AMPA}}$	${\tau }_{\mathrm{GABA}}$
−70 mV	−70 mV	−70 mV	−45 mV	−60 mV	50 nS	$\frac{30\mathrm{nS}}{N}$	0.5 nF	20 nS	20 nS	2 ms	5 ms

(i) Synaptic parameters (EE)
Synapse	Presynaptic τ	$p_0$	Factors	Postsynaptic ${\tau }_s$	$\tilde{\alpha }$
Static	–	0.5 (M)	–	100 ms	1 − exp(−0.25)
Facilitating	${\tau }_F=500\mathrm{ms}$	0.25 (M)	$f_F=0.25$ (M)	100 ms	1 − exp(−0.25)