Public defence, Neuroscience and Biomedical Engineering, MSc (Tech) Mikael Laine

Title of the thesis: Algorithmic control of multi-locus transcranial magnetic stimulation: motor mapping and pulse delivery

Thesis defender: Mikael Laine 
Opponent: Professor Axel Thielscher, Technical University of Denmark
Custos: Professor Matti Hämäläinen, Aalto University School of Science

Transcranial magnetic stimulation (TMS) activates brain cells wirelessly. A coil held against the scalp produces a brief magnetic pulse, which induces an electric field in the brain, causing neurons to fire. TMS is used in brain research, planning of brain surgery, and in treatment of brain disorders such as depression, obsessive–compulsive disorder, and migraine. 

Although the method is four decades old, the way it is used has barely changed. An operator holds a single coil by hand, hunts for the right spot on the scalp and delivers the pulses one by one. The work is slow, the results depend on the operator's skill, and stimulating whole networks of brain areas is practically difficult, if not infeasible. 

In his doctoral thesis, Mikael Laine developed methods and instrumentation that hand this work over to algorithms. The work builds on multi-locus TMS (mTMS), a technology developed at Aalto University in which the single coil is replaced by an array of five overlapping coils. By adjusting the current in each coil, the stimulating electric field can be manipulated electronically, for example to achieve the effect of moving the stimulation site. 

The thesis produced four results, with the author's main contributions in stimulation control software. The first is a method for locating the patch of cortex that controls a given finger movement. It reasons probabilistically about every pulse and chooses the next one to be as informative as possible, reaching the precision of a conventional protocol with less than half the pulses, down to millimeter scale. The second is an automated search for the best stimulation spot and orientation, which finds them in roughly four minutes and more accurately than manual work. The third is a five-channel mTMS device built to medical safety standards and installed at a brain research institute in Tübingen, Germany — the first time such a system has been deployed in a hospital. The fourth is a pulse-control technique that shortens the gap between successive pulses from seconds to microseconds, unlocking new stimulation protocols targeted at spatially distributed brain networks. 

Brain disorders are among the largest contributors to the global burden of disease. The thesis concludes that relaxing these long-standing constraints makes TMS faster, less operator-dependent, and able to address questions about the brain that were previously out of reach.

Key words: transcranial magnetic stimulation, multi-locus, motor mapping, localization, closed-loop, pulse-width modulation

Thesis available for public display 7 days prior to the defence at Aalto University's public display page. 

Contact Information: 
https://www.linkedin.com/in/mikael-h-laine/