# Biological Basis of the Computational Model Code The code provided is a computational model that simulates motor cortical neurons, specifically pyramidal neurons (PYN) and fast-spiking interneurons (FSI), to study their interactions and dynamics. This model is grounded in several key biological principles: ## Neuron Types - **Pyramidal Neurons (PYN/PY):** These are excitatory neurons typically found in the cerebral cortex. They are characterized by their pyramid-shaped cell body and the long axons that they extend, allowing them to connect with distant brain regions. The model implements twenty low-threshold spiking pyramidal neurons, reflecting their predominant role in excitatory neurotransmission in cortical circuits. - **Fast-Spiking Interneurons (FSI/FS):** These are inhibitory neurons known for their rapid firing rates and crucial role in regulating cortical excitability and synchronizing neural activity. The model includes two fast-spiking interneurons to simulate their inhibitory influence on pyramidal neurons. ## Ion Channel Dynamics - **Ion Channels:** The code introduces several ionic mechanisms, including passive ("pas"), sodium (Na), and potassium (K) channels. Each neuron utilizes different ion channels (`mcIt`, `mchh2`, `mcIm`) to model their distinct electrophysiological characteristics. - **`ena` (Na reversal potential):** Set at 50 mV, reflecting the typical extracellular-intracellular sodium ion gradient. - **`ek` (K reversal potential):** Set at -100 mV, representing the potassium ion gradient critical for repolarizing the membrane after an action potential. - **Calcium channels (`mcCad`, `mcIt`):** Play a role in regulating intracellular calcium levels, influencing neurotransmitter release and neuronal excitability. ## Synaptic Dynamics - **Synaptic Interactions:** The model employs `tanhSyn` synapses to simulate connections between neurons. Pyramidal-Pyramidal (PY2PY), Pyramidal-Interneuron (PY2FS), and Interneuron-Pyramidal (FS2PY) interactions are modeled, emphasizing both excitatory and inhibitory synaptic communication. - **Excitatory Synapses:** Typical for pyramidal-pyramidal connections, they model glutamatergic transmission. - **Inhibitory Synapses:** Represented in interneuron-to-neuron connections, modeling GABAergic transmission. ## Neuronal Properties - **Resting Membrane Potential and Conductance:** The code sets specific values for resting membrane potentials (e.g., `e_pas`, `vtraub_mchh2`) and sodium and potassium conductances, reflecting the inherent electrical characteristics of these neurons. - **Q10 Factor (`celsius = 36`):** The model adjusts conductance properties according to temperature, set at 36°C, which is close to human body temperature. ## Noise and Variability - **Random Noise Influences:** The model incorporates random noise to simulate the variability observed in biological systems. This includes synaptic noise (`noiseSwitch`) and membrane noise (`MC_noisc`), which impact neuronal firing patterns. Overall, the model captures key aspects of motor cortical neuron functionality, highlighting both cellular and synaptic level dynamics. It reflects our understanding of how excitatory and inhibitory neurons interact to shape cortical network activity, a foundation for understanding complex brain functions and behaviors.