The provided code models synaptic transmission at excitatory synapses in the brain, focusing on AMPA and NMDA receptor dynamics combined with presynaptic short-term plasticity mechanisms. Here's a breakdown of the biological concepts implemented in the code: ### AMPA and NMDA Receptors - **AMPA and NMDA Receptors**: These are ionotropic glutamate receptors responsible for fast excitatory neurotransmission in the brain. AMPA receptors mediate rapid synaptic currents, while NMDA receptors contribute to slower synaptic components and are involved in synaptic plasticity and memory formation. - **Dual-exponential Conductance**: The code models the synaptic conductance changes over time using a dual-exponential function. This reflects the biological observation that synaptic responses have a rising phase (shorter time constant, `tau_r`) and a decaying phase (longer time constant, `tau_d`), mimicking the rapid activation and slower deactivation of these receptors. ### Short-term Synaptic Plasticity - **Presynaptic Short-term Plasticity**: This phenomenon includes both synaptic facilitation and depression. It modulates the efficacy of synaptic transmission over short timescales (milliseconds to seconds) based on the recent history of synaptic activity. - **Facilitation (Fac)**: An increase in synaptic strength due to repeated stimuli within a short period, modeled using a facilitation time constant (`Fac`), where the utilization of synaptic efficacy (`Use`) increases after each action potential. - **Depression (Dep)**: A reduction in synaptic strength due to the depletion of readily releasable synaptic vesicles, modeled using a depression time constant (`Dep`). It represents the probability (`Pv`) of vesicles being available for release. ### Key Biological Processes - **Utilization of Synaptic Efficacy (Use)**: The initial probability that a neurotransmitter vesicle will be released in response to an action potential. It is dynamically adjusted based on recent synaptic activity, influencing short-term plasticity. - **Normalization Factor**: Ensures that peak synaptic conductance occurs at the same time, reflecting the physiological constraint that synaptic responses must occur within a precise timeframe to encode information effectively. - **Random Synaptic Activation**: Simulates the stochastic nature of neurotransmitter release, influenced by probabilistic processes (`erand()`), capturing the inherent variability observed in biological synapses. The code provides a detailed model of synaptic currents and their modulation by short-term plasticity, helping to understand how synaptic efficacy and temporal dynamics contribute to neural processing and information integration in the brain.