The code provided is part of a computational model focusing on the simulation of extracellular electrical stimulation and its effects on neuronal activity. This type of model is central in computational neuroscience as it helps researchers understand how externally applied electrical fields affect neuronal behavior and can be used to explore mechanisms underlying neurostimulation therapies. ### Biological Basis #### Extracellular Stimulation Extracellular electrical stimulation involves applying an electric current or field outside a neuron or neural tissue to influence its activity. It is a non-invasive method commonly used in clinical and research settings, such as in deep brain stimulation, transcranial magnetic stimulation, or peripheral nerve stimulation. The code explicitly mentions two units for amplitude: microamperes (µA) and volts per meter (V/m), indicating it can simulate current- or field-based stimulation paradigms. #### Temporal Parameters The parameters `DEL`, `DUR`, and `AMP` are biologically significant for extracellular stimulation: - **DEL (Delay):** Represents the latency period before the stimulation phase starts. In a biological context, this could mimic synchronization timings when applying stimuli in vivo. - **DUR (Duration):** Corresponds to the length of time the stimulation is applied during one phase. The duration of stimulus application is crucial as it affects the ability of the stimulus to evoke neuronal responses. Short stimulation might elicit action potentials, while prolonged application could lead to adaptation or desensitization. - **AMP (Amplitude):** The strength of the stimulus. Biologically, amplitude determines the extent of tissue activation. A higher amplitude can recruit more neurons or axons within a neural structure. #### Anodic and Cathodic Stimulation The plot settings in the code suggest considerations for anodic (positive polarity) and cathodic (negative polarity) stimulation. The biological effect of stimulation can differ between anodic and cathodic pulses: - **Anodic Stimulation:** Generally hyperpolarizes the membrane potential and can deactivate neurons temporarily. It is typically used for just the brief interruption of neuronal firing. - **Cathodic Stimulation:** Depolarizes the membrane potential, more effectively initiates action potentials, and is commonly used for neural activation. #### Simulation Goals The aim of such extracellular stimulation models is to predict and understand the effects of different stimulus parameters on neuronal circuits. This understanding aids in optimizing stimulation protocols for clinical interventions, such as neuromodulation therapies for Parkinson's disease, epilepsy, or depression. ### Conclusion This code provides a way to simulate how different temporal and intensity parameters of an extracellular stimulus can affect neurons or neural tissues. By manipulating these parameters, researchers can correlate stimulation patterns with neuronal responses, aiding in the design of effective stimulation-based treatments and understanding the underpinning biological mechanisms.