This review is devoted to the analysis of studies and implementations related to the use of focused ultrasound for functional effects on neuroreceptor structures. Special attention was paid to the stimulation of neuroreceptor structures in order to input sensory information to humans. This branch of medical and phys iological acoustics appeared in Russia in the early 1970s and was being efficiently developed up to the late 1980s. Then, due to lack of financial support, only individual researchers remained at this field and, as a result, we have no full fledged theoretical research and practical implementations in this area yet. Many promising possibilities of using functional effects of focused ultrasound in medicine and physiology have remained unimplemented for a long time. However, new interesting ideas and approaches have appeared in recent years. Very recently, very questionable projects have been reported related to the use of ultrasound for targeted functional effects on the human brain performed in some laboratories. In this review, the stages of the development of scientific research devoted to the functional effects of focused ultrasound are described. By activating the neuroreceptor structures of the skin by means pulses of focused ultrasound, one can cause all the sensations perceived by human beings through the skin in everyday life, such as tactile sensations, ther mal (heat and cold), tickling, itching, and various types of pain. Stimulation of the ear labyrinth of humans with normal hearing using amplitude modulated ultrasound causes auditory sensations corresponding to an audio modulating signal (pure tones, music, speech, etc.). Activation of neuroreceptor structures by means of focused ultrasound is used for the diagnosis of various neurological and skin diseases, as well as hearing dis orders. It has been shown that the activation is related to the mechanical action of ultrasound, for example, by the radiation force, as well as to the direct action of ultrasonic vibrations on nerve fibers. The action of the radiation force is promising for the realization of the possibility of blind and even deaf and blind people to perceive text information on a display using tactile sensations caused by ultrasound. Very different methods of using ultrasound for local stimulation of neuroreceptor structures are discussed in this review. Among them are practical methods that have been already tested in a clinic, as well as pretending to be sensational methods that are hardly feasible in the foreseeable future.
Short pulses of focused ultrasound can stimulate the superficial and deep-seated receptor structures of human tissues and induce different somatosensory sensations including, in particular, pain sensations. Focused ultrasound as a new artificial stimulus for inducing pain has a number of advantages related with its non-invasiveness, the possibility of the precise control of stimulus parameters and the location of its action. The experimental procedures and the results of the application of focused ultrasound as a painful stimulus in physiological research and in clinical practice are discussed. Data concerning various kinds of pain sensations, values of ultrasound thresholds of pain in different parts of the hand, as well as the discussion of the main effective factors of focused ultrasound responsible for the induction of pain, are presented in this review.
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