Effect of continuous and modulated ultrasound on fish neurons.

Currently, transcranial ultrasound stimulation (TUS) is being intensively developed as a new non-invasive method of neuromodulation. A convenient model for demonstrating ultrasonic neuromodulation is the nervous system of fish. Experiments have been carried out on Goldfishes. We have recorded general swimming reaction and turning reaction of fishes in the special chamber which bottom had been divided into sectors. We observed decrease of general swimming reaction and turning reaction after influence of continuous ultrasonic waves of therapeutic intensities (f = 0.88 MHz), when intensity was more than 0.7 W/cm2, and increase of these responses at intensities less than 0.1 W/cm2. Application of modulated ultrasonic fields as an acting factor produced changes of activity of fishes dependent on a modulating frequency. The action spectra have been received using an amplitude modulation (AM) of low frequency. This spectra reflect the work of the whole brain (tests of change of a general swimming reaction of fishes), and the work of identified Mauthner’s neuron, that is responsible for turning response of fishes. The action spectrum for Mauthner’s neuron is more expressed and contains three kinds of frequencies by the action on fishes activity: frequency of activation (8 Hz), partially depressing (6, 10 Hz) and neutral (3, 7, 9 Hz). Spectra are received at equienergy action АМ of ultrasonic sound irrespective of a modulating frequency (porosity = 2) and spatial average and temporal average intensities of 0.35 W/cm2. From an action spectrum we can conclude, that on one modulating frequency effects of a carrier frequency are relaxed, and on others strengthen. This approach can find application in ultrasonic therapy when it is necessary to make ultrasonic action more effective and to decrease potential hazard of action due to the cavity action.