Behaviorally measured refractory periods are lengthened by reducing electrode tip exposure or raising current.

Measured the effects of current and tip surface area on stimulation parameters required to produce a constant rate of self-stimulation of lateral hypothalamic sites or of circling when stimulating medial brain stem sites. Data from 20 male Wistar rats show that thresholds for circling decreased when tip surface area was decreased to 0.01 mm–2. Refractory period curves for both circling and self-stimulation were shifted to slightly longer intrapair intervals when tip surface area was decreased or current was increased. This suggests that long refractory period axons make larger contributions when current density is increased. Chronaxies were not lengthened by small tip exposures but were reduced when electrodes were placed far lateral to the circling substrate. Threshold differences between axons stimulated by different tip exposures and currents are discussed. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)