New Technologies for Neuromodulation

Non-invasive neural stimulation techniques are of increasing importance as devices move from the lab to the clinical environment. One such technology-transcranial magnetic stimulation-has already made the transition and is currently used by clinicians to treat depression. This device has several drawbacks, such as a limited ability to focus its energy to a relatively small region and to distribute energy to deep structures. This thesis simulates an inhomogeneous human brain under transcranial magnetic stimulation. The models developed indicate that regions of high conductivity and permittivity may be the key to overcoming the limitations of current TMS technology. Specifically, models of 1mm-sized particles of high conductivity and permittivity increased the induced current in deep regions by a factor of 600,000, indicating that some modification to the delivery method of TMS may drastically increase its effectiveness and usability. Unlike other forms of stimulation, acoustic energy has not been explored in great depth in relation to neural stimulation. This thesis explores the possibility of using ultrasound to focally target and non-invasively stimulate rodents in vivo. While the mechanism by which ultrasound works to alter neural activity is difficult to pinpoint, in vivo testing with a variety of ultrasound frequencies, powers, and delivery protocols may lead to a breakthrough in the field. Furthermore, this thesis outlines a method for stimulating neural activity with ultrasound by way of heating specific regions. Thesis Supervisor: Edward S. Boyden Assistant Professor, M.I.T. Media Lab Table of