Assistant Professor of Neurosurgery Harvard Medical School

Assistant Investigator Neurosurgery, Mass General Research Institute

Research Staff Neurosurgery, Massachusetts General Hospital

PhD Seoul National University 2010

brain computer interface; cochlear implant; cortical pyramidal neurons; deep brain stimulation; electric stimulation; magnetic stimulation; microcoil implant; microelectrode; neural prosthesis; retinal ganglion cells; retinal implant

Electrical stimulation is currently used to treat a wide range of cardiovascular, sensory and neurological diseases. Despite its success, there are significant limitations to its application, including incompatibility with magnetic resonance imaging, limited control of electric fields and decreased performance associated with tissue inflammation. Magnetic stimulation overcomes these limitations but existing devices (that is, transcranial magnetic stimulation) are large, reducing their translation to chronic applications. In addition, existing devices are not effective for deeper, sub-cortical targets.

To overcome such limitations, we developed a sub-millimeter coil and demonstrate that magnetic stimulation arising from this small coil can activate neurons in the rabbit retina. Interestingly, the results of both modelling and physiological experiments suggest that different spatial orientations of the coils relative to the retinal tissue can be used to generate specific neural responses. These results raise the possibility that micro-magnetic stimulation coils, small enough to be implanted within the brain parenchyma, may prove to be an effective alternative to existing stimulation devices (Bonmassar et al. Nat Commun 2012; Lee et al. US patent application 2014).

We have since shown that stimulation from such a coil can activate neurons of the sub-thalamic nucleus which is the major target of DBS for treatment of Parkinson’s disease (Lee et al. IEEE TNSRE 2015) and can also strongly activate cortical pyramidal neurons of the prefrontal cortex (PFC) which are the major target of transcranial magnetic stimulation (TMS) for treatment of depression (Lee et al. IEEE TNSRE 2016).

We are now developing a novel coil design that is much smaller but more effective than that of the existing micro-coil so as to implement a 3-D high density coil array that can be used as a the high-resolution cortical prosthetic device. In preliminary testing, we have found that the new design is working well in both in vitro and in vivo animal experiments (Lee et al. Sci Adv 2016). As the result of our recent work, we are now beginning several collaborations with both US and international laboratories to assess the clinical effectiveness of this new coil.