Short-latency prepulse inhibition of the trigeminal blink reflex

Abstract Prepulse inhibition (PPI) refers to the phenomenon in which a weak sensory input, that by itself does not reliably induce a startle reflex, suppresses the startle reflex induced by a subsequent strong sensory stimulus. A major challenge in studying PPI is the incomplete understanding of the startle reflex pathway as well as inhibition mechanisms. Here we focused on short-latency PPI of the trigeminal blink reflex R1 signal with an oligosynaptic reflex arc to clarify whether the PPI mechanism involves GABA-A equivalent inhibition. The reflex was elicited by electrical stimulation of the supraorbital nerve, and was recorded from the ipsilateral lower eyelid using an accelerometer. The stimulus intensity was 1.5 times the R1 threshold for the test stimulus and 0.9 times for the prepulse. The prepulse–test interval (PTI) was 5–150 ms. Results yielded two distinct inhibitions with different time scales; early inhibition peaking at 40-ms PTI or earlier, and a later one after 80-ms PTIs, which corresponds well to the common early and late components of inhibitory post synaptic potentials. There is clinical benefit to understanding the relative behavior of these two components in inhibitory function related diseases.