The provided code snippet is part of a computational neuroscience model focusing on the granule cells (GrCs) of the cerebellum and their synaptic interactions. Below is a biological overview relevant to the code: ### Biological Basis #### Cerebellar Granule Cells (GrCs) - **Anatomy and Function**: Granule cells are among the smallest and most numerous types of neurons in the brain, found predominantly in the granular layer of the cerebellum. They play critical roles in motor coordination and cognitive functions by relaying input signals from mossy fibers to Purkinje cells via parallel fibers. - **Synaptic Inputs**: GrCs receive excitatory inputs from mossy fibers, which carry sensorimotor information to the cerebellum. #### Synaptic Transmission - **AMPA and NMDA Receptors**: The code models synaptic transmission at granule cells using both AMPA and NMDA receptors. These receptors are types of glutamate receptors that mediate fast synaptic transmission in the central nervous system. - **AMPA Receptors**: Responsible for fast excitatory synaptic transmission. The code creates AMPA synapses (`createsyn`) on specific dendritic compartments of the granule cell. - **NMDA Receptors**: These are slower and contribute to synaptic plasticity due to their voltage-dependent Mg²⁺ block, which is relieved upon depolarization, allowing Ca²⁺ influx, which is crucial for synaptic plasticity mechanisms such as Long-Term Potentiation (LTP). #### Simulation of Synaptic Activity - **NetStim and NetCon**: The code uses `NetStim` and `NetCon` to simulate synaptic input trains to the granule cells, mimicking the action of mossy fiber inputs. - **NetStim Objects**: Represent artificial spike trains with specified frequency, number, and start time, corresponding to different synaptic stimulation protocols. - **NetCon Connections**: These connect the `NetStim` outputs with the synaptic inputs on the granule cell, thereby modeling the synaptic activation of AMPA and NMDA synapses. #### Experimental Protocols - **Stimulation Protocols**: Different frequency protocols are employed to investigate the granule cell's responses to varying rates of input. These capture the cell’s adaptation to different input patterns, thereby reflecting different physiological conditions and behavioural states. #### Experimental Conditions - **Temperature and Initial Membrane Potential**: The model is set to run at 32°C, which is close to physiological temperature, and a typical resting membrane potential for neurons (-70 mV) is used. These parameters ensure that the simulation reflects in vivo conditions closely. #### Analysis and Output - **Membrane Potential Recording**: The code records the soma membrane potential over time, providing insights into the electrical behavior of the granule cell in response to synaptic inputs via AMPA and NMDA receptors. - **Data Storage and Visualization**: The membrane potential data is saved and visualized, enabling the study of the temporal dynamics of granule cell activity in response to various mossy fiber input patterns. In summary, the code aims to model and investigate the behavior of cerebellar granule cells under various synaptic input conditions, focusing on the interplay between fast and slow synaptic transmission mediated by AMPA and NMDA receptors, respectively. It closely mirrors biological processes involved in the functioning and modulation of neuronal circuits in the cerebellum.