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Publisher Summary This chapter discusses a variety of nerve structures that can be excited with focused ultrasound (US). Stimulation of the human arm with short stimuli results in various sensations similar to natural stimulation; with the center of the focal region within the skin, the stimuli of increasing intensity produced sensations of touch, tickling, warmth, cold, itching, and pain. When the center of the focal region is projected into the deep structures of the arm, only the pain sensations appear, their character depending upon the type of the tissue (soft tissues, bone, and joints). Stimulation of the same spots could result either in cold or in warmth sensations. Electrophysiological experiments exhibit that single mechanoreceptors—Pacinian corpuscles—and receptor structures of the frog's labyrinth can be excited by the focused US. Tactile sensations are because of excitation of the skin mechanoreceptors, whereas the temperature and pain sensations may involve the direct excitation of the nerve fibers. The comparative investigation of parameters to characterize the US propagation in the medium exhibit the main active factor in US stimulation is of a mechanical nature, that is, medium displacement in the focal region. With certain parameters of the stimulus, the local heating of the tissue at the place of stimulation is also involved. |
