Analysis of Single-Unit Activity in the Cerebral Cortex

Publisher Summary The extracellular spiking activity of single units is usually recorded by inserting a very fine needle (micro-electrode) into the cortex while recording the voltage at the tip of the electrode. Living cells are characterized by having a potential difference across their membranes with the inside negative relative to the outside. Active nerve cells are characterized by having different membrane potential at different sites. Such differences result in currents flowing through the salt solutions both inside and outside the cell. The currents, in the extracellular fluid, set potential differences that can be recorded by a micro-electrode. The electric field induced by a surface dipole depends on the dipole moment, the area, the orientation of the surface, and the distance from the dipole. The statistics of the activity of a single unit is most commonly studied by means of the renewal density function. This function describes the rate of firing of a single unit as a function of time that has elapsed since it fired.