With National Science Foundation support, Drs. Shimojo, Gabrieli, Maeda, and colleagues will conduct a two-year project aimed at developing and validating a new transcranial magnetic stimulation coil device. A transcranial magnetic stimulator (TMS) coil produces relatively focal magnetic current which can be used non-invasively (outside the skull) to safely create "virtual brain lesions" and to transiently modulate neural activity. It can probe brain areas at different points in time during the performance of a psychological task and thereby assess the causal relationship between brain activity at the targeted location and components of task processing. It is particularly powerful in combination with neuroimaging, which can provide activation maps and precise stereotactic reference frames (anatomical MRI) for accurate and task-relevant TMS targeting. TMS provides a means to study of causal relationships between brain activity and behavior by induction/facilitation or extinction/inhibition of an effect, a significant advantage over other brain imaging techniques that in general offer only correlational effects. The device to be developed in this project will allow rapid switching of current in the TMS coil in a novel fashion that allows much greater range of precisely matched control conditions, and it is particularly useful in neuroimaging settings.
More specifically, the proposed device will deliver three kinds of stimulation without having to move or switch coils, and all while causing similar sensations hence being unnoticed to the participants. First, I can produce real TMS. Second, it can produce sham TMS: by manipulating the current in each loop of the coil, most of the induced electric field will be cancelled out, hence resulting in no substantial physiological effect. Third, the device can produce real TMS with reversed current direction. Many brain regions have optimal TMS current direction to disrupt or evoke an effect, and by reversing the current direction in the coil, this type of TMS applies non-optimal stimulation while maintaining identical subjective sensation and induced electric field. In many cases, the coil can be set so that this reversed current is ideal to stimulate another (usually the contralateral) site. The device will be validated using well-established tools and paradigms in the fields of cognitive neuroscience and TMS. In particular the proposed device will be validated with respect to (1) its physical properties using a search-coil electric circuit, (2) associated subjective sensations, (3) in behavioral paradigms of motor physiology and (4) visual psychophysics, and (5) electroencephalographic (EEG) recordings of the TMS-evoked responses and behavior/TMS interaction.
Intellectual Merit. This proposed TMS device is superior to conventional TMS in five ways. First, it can be used in fluently and simultaneous with brain imaging studies in which moving or switching coils is highly undesirable. Second, it can be used to interleave different sham and control conditions with great control. Third, it can be used in a double blind designs, in which neither the experimenter apply the TMS nor the subject know whether the TMS is real, sham TMS, or real-TMS in the reverse direction. Fourth, the device can be used to produce consecutive and controlled activations of either the same brain area or two different neural structures, without the participant's awareness. Fifth, it can be used to investigate the physiologic and behavioral interactions of two consecutive stimuli in the same or different current directions.
Broader Impacts. Undergraduate and graduate students, postdoctoral fellows, and staff members will receive interdisciplinary training in psychophysics, electrical engineering, neurophysiology, and signal processing. The proposed device will be used by cognitive, clinical, and TMS neuroscience research communities to enable new avenues for more sophisticated and novel research techniques for better understanding of brain function, pathophysiology of neuropsychiatric disorders, and the mechanism of action of TMS. Findings and techniques will be disseminated through conferences, journals, and our laboratory web-sites. Circuit diagrams, theories, and results of our validation studies will be available at those web-sites. Upon success of this proposal and with demand from the research community, this device should become commercially available from a major manufacturer.
