Using intracranial electrical stimulation to study the timing of prepulse inhibition of the startle reflex

Due to the short latency and briefness of the startle reflex, event-related inhibition of startle has high temporal resolution and is useful for studying the hierarchical organization of sensorimotor gating and motive-motor gating. In this article, we describe methods for measuring the inhibitory effects of electrically stimulating each of the following four brain structures on startle in awake rats: the inferior colliculus (IC), the deeper layers of the superior colliculus (SC), the pedunculopontine tegmental nucleus (PPTg), and the ventral pallidum (VP). These four brain structures have been reported to be important in mediating sensorimotor or motive-motor gating. Startle responses are elicited by either intense noise bursts or electrical stimulation of the principal trigeminal nucleus. The time course of the IC-inhibited startle reflex is used as a standard for estimating timing of the neural transfer of startle-inhibitory information to motor outputs. We also discuss how these methods can be used in combination with neuropharmacology.