The provided code is a component of a computational model simulating neuronal electrical activity with a specific focus on current modulation by ion channels. Here's a breakdown of the biological basis: ### Biological Basis 1. **Neuronal Excitability:** - Neurons express various ion channels on their membranes that influence excitability by modulating membrane potential and action potential firing. This script appears to model changes in membrane potential (`v`) in response to different ion channel conditions. 2. **Ion Channels and Current:** - **gM Channel (M-type potassium channel):** The code references "gM = 0" which indicates the removal of M-type potassium current. M-channels are non-inactivating potassium channels that contribute to setting the resting membrane potential and modulating neuronal excitability. Blocking these channels (gM = 0) would typically result in increased excitability and altered action potential dynamics. - **gSK Channel (Small conductance calcium-activated potassium channel):** "gSK = 0" reflects the inhibition of SK channels. SK channels are activated in response to intracellular calcium levels and contribute to the afterhyperpolarization (AHP) following an action potential, thus affecting repetitive firing and the firing rate adaptation of neurons. 3. **Parameters for the Simulations:** - The parameters `dur1`, `dur2`, and `dur3` are likely defining different phases of the stimulus or recording periods that influence how long the simulations track changes in membrane voltage under different conditions. For both figures (6A and 6B), the duration parameters are different, reflecting varied experimental conditions or hypotheses being tested. 4. **Experimental Conditions:** - The script sets different initial holding currents (`ihold`) and stimulus amplitudes (`amplitude`) depending on the condition being simulated (control, gM channel blocked, gSK channel blocked). These parameters are critical in a neuronal model as they influence the starting conditions for membrane potential and simulate changes in stimulus intensity. 5. **Figures Functionality:** - The code generates plots for two scenarios, possibly representing different neuronal responses in experimental setups. Each condition is likely plotted to show the differences in voltage response over time (represented by vectors `t` and `v`) in control versus drug-modulated states. ### Conclusion Overall, this code simulates and visualizes how blocking specific ion channels—M-type potassium channels and calcium-activated potassium channels (SK)—modulates neuronal membrane potential and excitability. This modeling is crucial in understanding intrinsic neuronal properties, how they influence signal propagation, and the broader impacts on neural circuits and behavior.