The provided code models the electrical activities within a computational model of neural circuits, specifically targeting the subthalamic nucleus (STN) and globus pallidus (GP) in the basal ganglia, which are crucial components of the motor control system in the brain. This model is rooted biologically in the following key aspects: ### Subthalamic Nucleus (STN) The STN is a small, lens-shaped nucleus in the brain involved in regulating movement. In Parkinson's disease, the STN is often a focus of deep brain stimulation (DBS) to alleviate motor symptoms. The model represents STN neurons and incorporates various aspects of neuronal electrophysiology: - **Ionic Currents**: The model includes ion-specific channels such as sodium (\( \text{I}_\text{Na} \)), potassium (\( \text{I}_\text{K} \)), calcium (\( \text{I}_\text{Ca} \)), and leak currents. These are critical for generating action potentials and synaptic transmission. - **Gating Variables**: Variables like \( m \), \( h \), and \( n \) are gating variables for ion channels, governing their opening and closing in an activity-dependent manner. - **Calcium Dynamics**: The intracellular calcium concentration (\( \text{Ca} \)) is regulated as it affects not only electrical activity but also neurotransmitter release and synaptic plasticity through after-hyperpolarization (\( \text{I}_\text{AHP} \)). - **Thalamic and Synaptic Currents**: The model indicates synaptic currents (\( \text{isyn} \)) as well as local field potentials (LFPs), representing local synaptic network interactions and external modulation through electrical stimulation. ### Globus Pallidus (GP) The GP is another basal ganglia nucleus, further divided into internal (GPi) and external (GPe) segments. It plays an essential role in controlling voluntary movement, influenced heavily by STN output. - **Currents and Dynamics**: Similar to the STN, it includes sodium, potassium, calcium currents, and additional gating dynamics for regulating these channels. - **Synaptic Interactions**: The GP also receives synaptic input from the STN, modeled here (\( \text{isyng} \)), emphasizing its interaction with STN activity and responsiveness to applied currents. ### Stimulation Protocol Electrodes are simulated on the STN neurons to mimic local and non-local stimulation influences, modeling deep brain stimulation techniques used clinically. - **Stimulation Currents**: Defined through parameters \( \text{Istim} \) affecting specific neurons, reflecting the spread and intensity of electrical signals. - **Delay Components**: Simulation of synaptic delays and their cumulative effects on the network encourage realistic modeling of temporal dynamics in neural communication. ### Biological Significance This model aims to simulate the dynamics of the STN-GP network, relevant for understanding basal ganglia disorders like Parkinson's disease. It demonstrates how interactions between these components under normal and stimulated conditions can affect network output and motor control. Overall, the model is a computational attempt to dissect the pathophysiological processes of these neural circuits, offering insights into potential therapeutic interventions through parameters like electrical stimulation (DBS) and its effects on neuronal and network dynamics.