# Biological Basis of the Computational Model The provided code models synaptic transmission involving AMPA and NMDA receptors at a synapse, incorporating elements of presynaptic short-term plasticity. Here's an overview of the biological aspects represented by this code: ## Synaptic Receptor Dynamics ### AMPA and NMDA Receptors - **AMPA Receptors**: These are ionotropic glutamate receptors responsible for fast excitatory synaptic transmission in the brain. The code models their conductance with a dual-exponential profile characterized by rise (`tau_r`) and decay (`tau_d`) time constants. - **NMDA Receptors**: Like AMPA receptors, NMDA receptors are also ionotropic glutamate receptors, but they have distinct properties, such as voltage-dependent Mg²⁺ block and permeability to Ca²⁺ ions in addition to Na⁺ and K⁺ ions. In the code, the same gating dynamics are assumed for simplicity, although typically NMDA conductances would have much slower kinetics compared to AMPA. - **Reversal Potential (`e`)**: Set to 0 mV, consistent with the mixed cationic nature of these receptors. The conductance change follows a difference of two exponential terms (`A` and `B`), reflecting the rapid activation and slower deactivation of synaptic currents typical of postsynaptic receptors. ## Short-Term Synaptic Plasticity ### Presynaptic Mechanisms - **Utilization of Synaptic Efficacy (`Use`)**: Represents the probability that a presynaptic vesicle will release neurotransmitter upon an action potential. This parameter captures the baseline release probability inherent to the synapse. - **Depression (`Dep`) and Facilitation (`Fac`)**: Describe how synaptic strength changes in response to repetitive stimulation: - **Depression**: The code uses a time constant (`Dep`) describing how quickly the resource pool recovers after depletion due to vesicle release. It reflects a transient reduction in synaptic efficacy following repeated activity. - **Facilitation**: Characterized by a time constant (`Fac`), facilitation represents a temporary increase in synaptic release probability following prior activity, enhancing the synaptic response over short timescales. ### Synapse Model Variables - **Pr and Pv**: - **Pr** (release probability): Calculated as the product of `Pv` (vesicle availability) and `u` (running efficacy), reflecting the likelihood of neurotransmitter release. - **Pv**: Reflects the availability of vesicles in the presynaptic terminal, analogous to a pool of resources that can be released. Overall, this code integrates the dynamics of receptor behavior with the modulating effects of presynaptic short-term plasticity, described using parameters derived from experimental and theoretical studies (e.g., Fuhrmann et al. 2002). This provides a mechanism by which synapses can display complex patterns of change in response to varied patterns of activity, aligning with observations in biological neural systems.