Transcranial Focused Ultrasound for Non-invasive Neuromodulation of the Visual Cortex.

Lu, Gengxi; Qian, Xuejun; Castillo, Johnny; Li, Runze; Jiang, Laiming; Lu, Haotian; Shung, K Kirk; Humayun, Mark S; Thomas, Biju B; Zhou, Qifa

Currently, blindness cannot be cured and patients' living quality can be compromised severely. Ultrasonic neuromodulation is a promising technology for the development of non-invasive cortical visual prosthesis. We investigated the feasibility of transcranial focused ultrasound (tFUS) for non-invasive stimulation of the visual cortex to develop improved visual prosthesis. tFUS was used to successfully evoke neural activities in the visual cortex (VC) of both normal and retinal degenerate (RD) blind rats. Our results showed that blind rats showed more robust responses to ultrasound stimulation compared to normal rats. (p<0.001, two-sample t-test). Three different types of ultrasound waveforms were used in the three experimental groups. Different types of cortical activities were observed when different US waveforms were used. In all rats, when stimulated with continuous ultrasound waves, only short-duration responses were observed at 'US on & off' time points. In comparison, pulsed waves evoked longer low-frequency responses. Testing different parameters of pulsed waves showed that a pulse repetition frequency higher than 100Hz is required to obtain the low-frequency responses. Based on the observed cortical activities, we inferred that acoustic radiation force (ARF) is the predominant physical mechanism of ultrasound neuromodulation.