# Biological Basis of the Computational Model The provided code models the interaction between interneuron cells and pyramidal cells through GABAergic synapses, with a focus on local calcium (Ca²⁺) dynamics at the synapse. Below are the key biological components and processes being modeled: ## Synaptic Interaction - **GABAergic Synapse**: The script represents synaptic transmission from interneuron cells to pyramidal cells via the neurotransmitter gamma-aminobutyric acid (GABA), which is inhibitory and causes hyperpolarization of the postsynaptic neuron. - **Point Process**: The `POINT_PROCESS` `interV2pyrD_STFD` symbolizes the specific synaptic point through which GABA is released, influencing the postsynaptic pyramidal neurons. ## Ion Dynamics - **Calcium Dynamics**: The model incorporates a local calcium pool at the synapse, which affects synaptic transmission and plasticity. This local pool is represented by variables such as `capoolcon`, `ICag`, and `Icatotal`. - **Equilibrium and Conductance**: The model reads the equilibrium potential and currents of calcium ions (`eca`, `ica`) to understand the ionic driving force that modulates synaptic strength. ## Synaptic Plasticity - **Weight Dynamics**: Synaptic weight (`W`), representing synaptic strength, is adjusted based on local calcium concentration. The model includes calculations for synaptic plasticity through functions `eta` and `omega`, which utilize calcium level thresholds to model activity-dependent changes (potentially long-term potentiation and depression). - **Facilitation and Depression**: The model accounts for short-term synaptic plasticity with terms like `F`, `D1`, and `D2`, representing facilitation and depression dynamics that modify synaptic efficacy temporarily. - **Thresholds and Learning Windows**: Calcium threshold for plasticity change, as well as learning rules through parameters like `lambda1`, `lambda2`, `threshold1`, and `threshold2`, determine when and how synaptic weights are updated, reflecting biological learning processes. ## Neuronal Excitability - **Membrane Potential Influence**: Synaptic current (`igaba`) affects the postsynaptic membrane potential based on the conductance (`g_gaba`) and the reversal potential (`Erev_gaba`), driving the neuron's response to synaptic input. - **Calcium-Mediated Feedback**: The intricate feedback loop involving calcium influx (`ICag`) due to synaptic activity and its subsequent impact on weight adaptation models the complex feedback systems in real neurons that facilitate adaptive learning and memory processes. ## Summary The code models an inhibitory synaptic transmission from interneuron to pyramidal cells, focusing on GABA release and calcium ion influence on synaptic plasticity. It captures essential biological processes such as neurotransmitter action, ionic movements, synaptic strength modulation, and short- and long-term plasticity—key components in understanding neural circuit dynamics and learning mechanisms in the brain.