Biological Basis of the Code

The code provided is oriented towards simulating and visualizing certain aspects of neuronal behavior, particularly focusing on the effects of the hyperpolarization-activated cation current (I_h) and the M-type potassium current (K_M). These ion currents are crucial in regulating neuronal excitability, rhythmicity, and response to synaptic inputs.

I_h Current

The I_h current, or hyperpolarization-activated cation current, plays a critical role in determining the resting membrane potential and the responsiveness of neurons. It is activated by membrane hyperpolarization, typically below the resting membrane potential. This current contributes to:

• Pacemaking Activity: In neurons with intrinsic oscillatory behavior, I_h helps in setting the rhythm of action potentials.
• Stabilization of Membrane Potential: I_h can stabilize the resting potential, making the neuron less sensitive to small depolarizing inputs.
• Rebound Excitation: It can lead to a phenomenon known as rebound excitation, where a neuron fires action potentials following a period of inhibition. This is reflected in the code by the increase in I_h by 300%, as indicated by the key 'ih3'.

M-type Potassium Current (K_M)

The M-type potassium current (K_M) is a non-inactivating current that is activated by depolarization and contributes to:

• Subthreshold Responsiveness: It helps to control the excitability of the neuron under subthreshold conditions, directly influencing repetitive firing properties.
• Regulation of Spike Frequency: The absence or reduction of the K_M current, as modeled in the case titled "No K$_M$," can lead to increased neuronal excitability.

Computational Model Insights

The code employs visualization techniques to simulate:

• F-I Curves: The frequency-current (F-I) curves assess how the frequency of action potentials varies with different levels of synaptic input current. The simulations under 'control' (black) and 'ih3' (red) indicate an examination of how increased I_h affects neuronal output.

• Rebound Curves: These are simulations of membrane potential traces, specifically looking at the neuron's activity following a period of hyperpolarization. The highlights in green and purple illustrate the effects of varying I_h levels on rebound behavior.

• Sag Curves: These visualize the voltage sag, essentially the initial hyperpolarization that relaxes back towards the resting potential, demonstrating the presence and functionality of I_h and K_M currents. This is significant in understanding how neurons react during prolonged inhibitory inputs.

Conclusion

Overall, the computational model aims to explore how modulations in I_h and K_M currents influence neuronal excitability and behavior. These ion channels are integral to neuronal dynamics, impacting rhythmic activities such as oscillations in thalamocortical neurons, cardiac pacing, and sensory neuron responsiveness. The provided code simulates and visualizes these biological processes, allowing for a deeper understanding of their mechanistic roles in neural circuitry.