The code provided is part of a computational neuroscience model that simulates the dynamics of a specific neural circuit in the brain, focusing on the basal ganglia and its interactions. This model appears to be inspired by experimental studies, specifically those related to the work of Magill et al. (2001), and is coded to explore specific conditions, such as those involving urethane anaesthesia. ### Biological System Modeled #### Basal Ganglia Circuitry The basal ganglia is a complex network of subcortical nuclei that are crucial for various functions, including motor control, procedural learning, and action selection. It comprises several key structures, including the striatum, subthalamic nucleus (STN), globus pallidus (GPe and GPi), and the substantia nigra. In this model: - **SD1 and SD2**: These represent the D1 and D2 receptor-expressing medium spiny neurons in the striatum, respectively. These neurons receive cortical inputs and are the primary input neurons to the basal ganglia. - **STN**: The subthalamic nucleus, which is involved in regulating movement and is known for its excitatory output. - **GPe and GPi**: The external and internal segments of the globus pallidus, respectively. GPe primarily provides inhibitory output to other basal ganglia components and GPi serves as a major output nucleus that projects to the thalamus, inhibiting it. #### Dopaminergic Modulation The models include parameters that simulate the effects of dopamine (DA) on neural activity. Dopamine is a critical neuromodulator in the basal ganglia, influencing motor and cognitive functions. Here, `dop1` and `dop2` represent tonic dopamine levels affecting different parts of the circuitry. #### Synaptic Dynamics The code includes parameters that simulate excitatory and inhibitory synaptic currents: - **Excitatory Synaptic Currents**: Modeled using AMPA and NMDA receptor components. - **AMPA**: Fast excitatory currents with a mean time constant (`mean_tau_AMPA`) of 2 ms. - **NMDA**: Slower, longer-lasting excitatory currents with a mean time constant (`mean_tau_NMDA`) of 100 ms. - **Inhibitory Synaptic Currents**: Primarily mediated by GABA receptors. - **GABAa**: Fast inhibitory currents with a mean time constant (`mean_tau_GABAa`) of 3 ms. #### Cell-specific Parameters Various parameters are specified for each nucleus, such as membrane time constants (`mean_tau_m`), resistances (`mean_R`), and spontaneous currents (`spon`). These parameters reflect the diverse intrinsic properties of different neuron types within the basal ganglia. #### Burst Dynamics The model includes a mechanism for generating burst firing, particularly for the STN neurons, which can exhibit burst-like activities. Parameters such as `mean_thetaCA` and `mean_alphaCA` control the burst characteristics. ### Pharmacological Modulation The code includes functionality for modifying synaptic weights based on simulated pharmacological conditions such as urethane administration. This anesthetic agent is known to affect synaptic transmission, and the model implements a reduction in glutamatergic weights and an increase in GABAergic weights to reflect such conditions. ### Summary In summary, the code models the complex interactions within the basal ganglia under specific conditions. It simulates various physiological and pharmacological states that affect neuronal and synaptic activities, providing a framework to study the underlying biological processes involved in motor control and modulation by neurotransmitters like dopamine.