Temporal summation of pulsate brain stimulation in normal and deafened cats

Behaviorally measured, electrical-stimulation thresholds were obtained from 11 electrodes permanently positioned in the auditory system and other brain loci. Number of pulses and interpulse intervals were varied to determine how detection thresholds were affected by stimulation parameters. Detection thresholds generally decreased with increased number of pulses and with shorter interpulse intervals. A method is presented to describe the parametric threshold data for each electrode in terms of three constants: a single-pulse threshold which characterizes the sensitivity of the placement; a time constant of temporal summation; and a compression factor which describes the range of threshold variation. For three placements in the vicinity of cochlear nucleus, bilateral cochlear destruction permanently altered parametric thresholds. In particular, single-pulse threshold was lowered by 9.2 dB; time constant of temporal summation was reduced by a factor of 100; and the compression factor was increased. Classic strength-duration time constants were determined using behavioral methods and were shown to be equal in magnitude to the greatly reduced time constants for temporal summation in the deafened animals. This implies that capacity for temporal integration may be substantially reduced or lost in at least the lower level of the auditory system following deafness.