Exp2Syn

Exp2Syn is a double-exponential synaptic conductance model used in neural simulations, notably within the NEURON environment. It represents a postsynaptic conductance change triggered by presynaptic events, with a rise and decay embedded in a two-time-constant kinetics.

Time course and equations: After a presynaptic spike, the synaptic conductance g(t) evolves as g(t) = gmax [exp(-t/τ2) − exp(-t/τ1)] for t > 0, where τ1 is the rise time constant (short) and τ2 is the decay time constant (long). The conductance is zero for t ≤ 0. The synaptic current is i(t) = g(t) [V(t) − Erev], with Erev as the reversal potential. The sign and magnitude of Erev determine whether the synapse is excitatory or inhibitory, and gmax (or weight) scales the peak conductance.

Parameters and implementation: Core parameters include τ1, τ2, Erev, and a conductance scale (often controlled by a weight or gmax in the simulator). In NEURON, Exp2Syn is a point process that receives presynaptic events (via a NetCon). Each event triggers the conductance change described above. The model is discrete-event driven and provides a straightforward, physiologically motivated approximation of synaptic kinetics.

Applications and usage: Exp2Syn is widely used to model fast excitatory (e.g., AMPA-like) and inhibitory (e.g., certain GABAergic) synapses with biologically plausible rise and decay times. It is a standard component in NEURON and is compatible with other simulation frameworks that implement similar double-exponential synaptic dynamics. The model is valued for its simplicity, numerical stability, and ability to reproduce characteristic post-synaptic conductance transients.