Top 10 us travel destinations 2014 on For example, an auditory threshold is the slightest perceptible sound and an excitatory threshold is the minimum stimulus that triggers an action potential in a neuron. Also called limen. See also absolute THRESHOLD; DIFFERENCE THRESHOLD. thrombosis ti. the presence or formation of a blood clot (thrombus) in a blood vessel. Thrombosis is likely to develop where blood flow is impeded by disease, injury, or a foreign substance. thrombotic adj. Top 10 us travel destinations 2014 2016.