Fig. 5.

(A) Dynamic clamp schematic: A computer (left), simulating a voltage-gated sodium conductance is reciprocally connected to a neuron (right). The cell's voltage determines the driving force on the simulated conductance and thus the current command sent to the amplifier; at each time step, the dynamic clamp computer uses the cell's voltage to update the state of its sodium conductance model. (B) Intracellular recording of a fast-spiking interneuron showing its ability to generate fast, nonadapting trains of action potentials. TTX application (Middle) blocks action potential generation. Dynamic clamp restoration of sodium conductance (Right; command current in red) permits the neuron to generate fast, nonadapting trains of action potential-like waveforms. (C) Maximum spike rate (Upper) and spike cost (Lower) as a function of Na⁺ channel activation rate (i), inactivation rate (ii), and channel density (iii). Black traces, average of normalized values for all cells; gray traces, normalized values for each cell.