Further reading
Voltage Clamp and Reversal Potentials
This game turns voltage-clamp traces into an inference problem: from a family of currents measured at fixed command voltages, estimate the voltage at which the current would reverse.
What voltage clamp does
A voltage clamp attempts to hold membrane voltage at a prescribed command value while measuring the current needed to maintain that voltage. In an ideal clamp, the recorded current is the negative of the membrane ionic current under the chosen sign convention. The game abstracts away the amplifier and shows the membrane current traces directly.
The model in the game
The activation variable m relaxes toward minf(V) = 0.5(1 + tanh((V - V0)/V1)). The current is Imem = m(V,t)(V - Erev). Once activation has settled enough, plotting sampled current against command voltage gives an approximate I-V relation.
Reading the traces
Currents at command voltages below Erev have the opposite sign from currents above Erev. If all tested commands lie on one side of Erev, the answer requires extrapolation rather than direct interpolation. That is realistic, but it is harder than the rounds where the sampled currents visibly bracket zero.
Experimental caveats
Real voltage-clamp data can be distorted by series resistance, capacitance transients, imperfect space clamp, leak subtraction, and channel kinetics that are too fast for the clamp. The game omits those complications so the central current-voltage logic is visible.
On-topic resources
- Voltage clamp: overview of the technique and its experimental purpose.
- Reversal potential: the voltage where a membrane current reverses direction.
- Hodgkin-Huxley model: conductance-based modeling built from voltage-clamp data.
- Nernst equation: equilibrium potentials for single permeant ions.