| Popis: |
Non-invasive brain stimulation techniques allow for excitation or inhibition of neural activity via externally applied stimuli. Recently, ultrasound (US) has been shown to stimulate neurons with better spatial localisation than existing electrical stimulation modalities. We present a review of the literature in both the central and peripheral nervous systems demonstrating a range of effects from de novo action potential generation in isolated cell preparations to cognitive responses in humans. However, several questions remain before the technique can become widespread. These include: methods to accurately model, and deliver, transcranial US to specific brain targets; the safety of the approach from both a mechanical and thermal standpoint; elucidation of the fundamental mechanisms through which acoustic perturbations result in nervous system modulation; and the development of monitoring techniques to confirm US focusing in vivo as well as to detect the induced effects. In this thesis, we focus on the delivery and safety aspects. We present numerical simulations using k-Wave and experimental measurements demonstrating focusing to areas of the visual cortex using ex-vivo human skulls with single-element transducers. We show that targeting of many areas can be achieved without the use of lenses or arrays. Furthermore, we conduct an in-depth safety review detailing the parameter spaces over which studies have been conducted and highlighting any damage areas. In current human studies the technique appears to be safe with minimal, if any, side effects. Finally, we report findings from a human pilot study with the aim of modulating sites within the visual cortex. We present direct evidence of strong non-specific auditory activation following bursts of US confirming previous animal studies. These effects can confound US neuromodulation trials and demands further attention before US can realise its potential as both a scientific instrument to probe brain function and as a therapeutic modality to modulate brain activity. |
