# Biological Basis of the Dorsal Column Fiber Model for SCS Waveform Determination The code provided models aspects of spinal cord stimulation (SCS), specifically focusing on neuronal responses in the dorsal column fibers. This is a computational model that simulates how electrical stimulation, delivered through implanted electrodes, can affect the activity of neuronal fiber systems, typically employed as a therapeutic intervention for managing pain. ## Key Biological Concepts ### Dorsal Columns The dorsal columns are major pathways within the spinal cord that carry sensory information. Primarily, they transmit touch, vibration, and proprioceptive information from peripheral sensory neurons to the brain. The fibers in these columns are heavily myelinated, which facilitates the rapid transmission of nerve impulses. ### Spinal Cord Stimulation (SCS) SCS involves applying electrical stimuli to the dorsal columns of the spinal cord to modulate nerve activity and thereby alleviate chronic pain. It works on the principle of altering pain signal transmission through modulation of nerve fibers. ### Pulse Waveforms The code models two main types of electrical pulse waveforms: - **Monophasic Pulses:** These consist of a single phase where current flows in one direction. The code defines a simple square waveform of a particular amplitude and pulse width (`PW`). - **Biphasic Pulses:** These involve two phases: typically, a positive (or cathodic) phase followed by a negative (or anodic) phase. This is designed to reduce net charge delivery that might damage tissues. The ability to simulate trains of each pulse type is important for understanding the cumulative effect of repeated stimuli, which is reflective of real-world SCS applications. ### Extracellular Potentials The model includes computation of extracellular potentials generated by electrical currents in the shape of the given waveform. This is crucial as such potentials influence the membrane potentials of nearby neurons, thereby affecting neuronal excitability and activity. ### Neuronal Compartments Neurons are represented in a compartmentalized manner, reflecting the biophysical properties of neuronal membranes. This allows the simulation of current flow and integration along neural fibers in response to external stimulation. ### Electrode Configuration Electrodes used in the simulations can be arranged in specific configurations, and the model accounts for the distances between electrodes (extracellular) and neurons. This spatial component is vital as the effect of SCS varies depending on electrode placement relative to targeted nerve fibers. ### Conductivity and Resistivity The model incorporates the electrical properties of tissue, represented through parameters like `sigma`, which reflects the conductance properties in different directions. The anisotropic resistivity can influence the spread of electrical stimulation in biological tissues. ### Importance Understanding how different waveforms affect dorsal column fibers can aid in optimizing SCS therapies. Improved models can guide electrode placement and stimulation parameters, maximizing therapeutic effects while minimizing side effects or tissue damage. The model simulations help predict how SCS influences neural activity, assisting in designing personalized treatments based on individual patient anatomy and pathology.