ELECTRICAL-STIMULATION OF NEURAL TISSUE TO EVOKE BEHAVIORAL-RESPONSES

This review yields numerous conclusions. (1) Both unit recording and b ehavioral studies find that current activates neurons (i.e., cell bodi es and axons) directly according to the square of the distance between the electrode and the neuron, and that the excitability of neurons ca n vary between 100 and 4000 mu A/mm(2) using a 0.2-ms cathodal pulse d uration. (2) Currents as low as 10 mu A, which is considered within th e range of currents typically used during micro-stimulation, activate from a few tenths to several thousands of cell bodies in the cat motor cortex directly depending on their excitability; this indicates that even low currents activate more than a few neurons. (3) Electrode tip size has no effect on the current density - or effective current sprea d - at far field, but tip size limits the current-density generated at near field. (4) To minimize neuronal damage, the electrode should be discharged after each pulse and the pulse duration should not exceed t he chronaxie of the stimulated tissue. (5) The amount of current neede d to evoke behavioral responses depends not only on the excitability o f the stimulated substrate but also on the type of behavior being stud ied.