# Biological Basis of the Code This code models synaptic transmission focusing on AMPA and NMDA receptor dynamics, which are crucial for fast excitatory synaptic transmission in the brain. The model incorporates short-term synaptic plasticity mechanisms as described by Fuhrmann et al. (2002) to simulate synaptic efficacy during neuronal communication. ## AMPA and NMDA Receptors AMPA and NMDA receptors are ionotropic glutamate receptors involved in excitatory synaptic transmission. Here's how they are represented in the model: - **AMPA Receptors**: These receptors mediate fast synaptic transmission with rapid activation and deactivation kinetics. The code models AMPA receptor conductance using a dual-exponential decay function, characterized by a rise time constant (`tau_r_AMPA`) and a decay time constant (`tau_d_AMPA`). - **NMDA Receptors**: NMDA receptors are involved in synaptic plasticity and have slower kinetics compared to AMPA receptors. They are sensitive to voltage due to a magnesium (Mg²⁺) block which must be removed for ions to flow through the receptor. Like AMPA, NMDA receptor conductance is modeled with dual-exponential decay functions (`tau_r_NMDA`, `tau_d_NMDA`). The Mg²⁺ block is modeled by `mggate`, a gating variable, following the kinetic model proposed by Jahr and Stevens (1990). ## Short-Term Synaptic Plasticity The model incorporates short-term synaptic plasticity mechanisms reflecting changes in synaptic strength over short time scales: - **Facilitation and Depression**: Synaptic facilitation is a temporary increase in synaptic strength due to previous activity, while depression is a temporary decrease. This is characterized by two time constants: `Fac` for facilitation and `Dep` for depression, representing how quickly the synapse recovers from being in an active state. - **Utilization of Synaptic Efficacy (`Use`)**: This parameter represents the probability of neurotransmitter release upon stimulation. It's dynamically adjusted based on facilitation and depression. ## Synaptic Transmission Dynamics - **Dual-Exponential Profiles**: The conductance profiles for both receptor types are modeled using dual-exponential functions, which are biologically relevant for capturing the time course of post-synaptic currents. - **Stochastic Synaptic Transmission**: A probabilistic approach is used to decide synapse activation, reflecting the biological variability of synaptic transmission. The random number generation ensures that the synaptic responses are not deterministic, capturing the inherent stochastic nature of neurotransmitter release. In summary, this code models two critical aspects of excitatory synaptic transmission in the brain—AMPA and NMDA receptor kinetics, and short-term synaptic plasticity. These elements are essential for understanding how neurons communicate and adapt their interactions in response to various stimuli.