# Biological Basis of the Code The provided code models synaptic transmission and plasticity between pyramidal cells and interneurons in the brain, emphasizing the dynamics of AMPA and NMDA receptor-mediated currents as well as short-term synaptic depression. Below is a breakdown of the biological elements captured by the model: ## Synaptic Components ### AMPA and NMDA Receptors - **AMPA Receptors**: These are ionotropic glutamate receptors responsible for fast excitatory synaptic transmission. The code models AMPA receptor dynamics, including rise and decay times (`Cdur_ampa`, `AlphaTmax_ampa`, `Beta_ampa`), reversal potential (`Erev_ampa`), and conductance (`g_ampa`). - **NMDA Receptors**: NMDA receptors contribute to synaptic transmission and are involved in synaptic plasticity due to their voltage-dependent nature and calcium permeability. The code accounts for NMDA receptor kinetics (`Cdur_nmda`, `AlphaTmax_nmda`, `Beta_nmda`), reversal potential (`Erev_nmda`), and conductance (`g_nmda`). ### Calcium Dynamics - The code includes a local calcium pool associated with NMDA receptor activity, reflecting the calcium influx through NMDA receptors (`ICan`) and its influence on synaptic plasticity. Parameters such as `Cainf`, `pooldiam`, and `tauCa` represent calcium concentration dynamics and coupling with receptor currents. ## Short-term Synaptic Plasticity - **Facilitation and Depression**: Short-term synaptic depression is modeled with variables like `D1`, `D2`, and corresponding decay times (`tauD1`, `tauD2`), affecting synaptic efficacy during repetitive activity. Facilitation is modulated with variables `F` and `tauF`, reflecting enhancement of synaptic transmission upon repeated stimulation. - **Activity-Dependence**: The code integrates calcium-dependent plasticity rules, where `eta` represents a learning rate modulated by calcium, and `omega` describes activity-dependent weight changes. The thresholds `threshold1` and `threshold2` denote calcium concentration levels influencing synaptic plasticity (akin to LTP/LTD processes). ## Synaptic Weight Dynamics - **Weight Changes**: Synaptic strength modulation is implemented with rules for weight updates (`W`) based on calcium dynamics and pre-defined limits (`Wmax`, `Wmin`). The model includes mechanisms to prevent extreme weight changes and normalize weight update rates (`dW_ampa`, `maxChange`, `normW`, `scaleW`). ## Stochastic Processes - **Random Processes**: The model incorporates stochastic elements (`unirand`) to simulate probabilistic synaptic transmission, which reflects the inherent variability observed in biological synapses. ## Conclusion The code effectively models synaptic interactions between pyramidal cells and interneurons, focusing on the roles of AMPA and NMDA receptors, calcium dynamics, and synaptic plasticity mechanisms. This allows the simulation of activity-dependent synaptic transmission changes, capturing both short-term dynamics and long-term modulation influenced by intracellular calcium signaling.